Jeanne, would you like some…peeeaaasss? License information here.
I was seven weeks deep when it hit me. Suddenly, I was in a chronic state of queasiness. Under most circumstances, I had it under control. Sure, I would gag every time I brushed my teeth, but (mostly) I could keep it all down. Then I went to my aunt Diane’s house for dinner.
Aunt Diane rolls with a crowd of self-made Italian chefs and, as a result, most of her cooking falls under the “rustic Italian” umbrella. It is not uncommon to see sitting in her cupboard a massive inventory of jarred plum tomatoes or for an entire section of her freezer to be dedicated to homemade vodka sauce, always frozen in those takeaway containers that originally brought us egg drop soup. Under normal circumstances, I’d be psyched to eat over.
I don’t recall the entire menu, but there is one side dish that has been forever burned into memory, and not in a good way. I remember starring at my plate, specifically at the heaping pile of sautéed peas. I kept rearranging the peas on my plate, sometimes spreading them out, sometimes piling them up. Then Diane looked at me and excitedly asked, “Jeanne, did you try my peas? I made them just for you!” I don’t know what compelled her to make these peas for me. Perhaps it was because I am a vegetarian and the rest of the meal involved meat? But, there they were, staring me down, and there Diane was, watching with anticipation, waiting for my approval.
Because I adore my aunt Diane and I wanted to make her happy (after all, she did just cook an entire meal for my small family), I scooped up a moderate amount of peas with my fork and deposited them in my mouth. I had to use every fiber of my being to chew them, and even more effort to actually swallow. My body was not cooperating and I had to implement a state of near meditation to keep them from coming back up. Luckily, I kept my cool and was able coerce my face into showing a smile while simultaneously telling my aunt and friend that her peas were delicious.
Credit: Jeanne Garbarino.
My husband picked up on my soaring level of discomfort and without missing a beat, ate all my peas when Diane wasn’t looking. We ended the evening with my stomach contents intact, but barely.
The next morning, as I was preparing my 18 month-old daughter’s daycare lunch, I remembered that we were provided with a parting gift of sautéed peas. I took them out of the fridge and proceeded to aliquot them into containers more suitable for a toddler. As I removed the lid, the onion-tinged aroma of Diane’s sautéed spring peas smacked me across my face. My body was clearly angry about what I had done to it the night before and, as if it were in a state of protest, I found myself sprinting to the bathroom where I began to puke.
From that day forth, I could not eat peas, let alone see or smell them, without eliciting extreme nausea. It didn’t matter what time of day, the mere presence of peas, although not necessary, was sufficient to make me toss my, well, peas.
It has long been known that nausea and vomiting are common symptoms of pregnancy. In fact, documentation of this phenomenon goes as far back as 2000 BC. However, the term “morning sickness” is a complete misnomer. For one, pregnancy-related nausea and vomiting is not just a morning thing. It can happen at any time of day. Second, the term “sickness” suggests a state of unhealthiness. We know that perfectly healthy pregnant women who deliver perfectly healthy babies experience morning sickness, and this type of nausea and vomiting is not an indicator of maternal and/or fetal health.
But, that doesn’t change the fact that it sucks.
Morning sickness, more appropriately known as nausea and vomiting in pregnancy (NVP), affects approximately two-thirds of women in their first trimester of pregnancy. In many cases, morning sickness subsides at the end of the first trimester. In other cases, the symptoms of morning sickness can last for the entire pregnancy. For both my pregnancies, I experienced morning sickness for the first 5 months.
I feel so lucky.
No one really knows the exact mechanisms responsible for the onset morning sickness. We do know that the drastic hormonal changes that occur during early pregnancy certainly play a role; however, these effects are likely indirect. For instance, estrogen levels do not differ between pregnant women with morning sickness and those who do not experience symptoms. Furthermore, there is no causal relationship between human chorionic gonadotropin (hCG), the early pregnancy hormone detected by pregnancy tests, and morning sickness, despite the fact that peak hCG levels and peak severity of pregnancy-related nausea and vomiting occur at approximately the same time.
Based on these observations, scientists suggest that the hormonal fluctuations in pregnant women can elicit different responses in an individual, rendering some extremely susceptible and others remarkably resistant to the same stimulus (with regard to nausea and vomiting). This begs the question: Is there a genetic predisposition to morning sickness?
While a “morning sickness” gene has not been identified, a few lines of evidence point toward a potential for inheriting the tendency. For instance, identical twins, are fairly likely to share a tendency to morning sickness. Also, you are more likely to experience morning sickness if your mom experienced it, too. Even though genetics may be involved, the onset of morning sickness is probably what scientists call “multifactorial,” a result of a very complex interaction between genetics and environment, making it difficult to find a treatment that is effective and safe for everyone.
Until more is known, we are stuck eating saltines and sour candy. At least it’s something, right?
Food aversions and morning sickness
Make them if you dare. Credit: Jeanne Garbarino.
For my first pregnancy, it was smoked salmon, which I probably shouldn’t have been eating in the first place. For my second pregnancy, it was peas. (Interestingly, my aunt Diane initially provided both foods, which, after that initial consumption, was immediately followed by the onset of morning sickness.) The mere sight of either peas or smoked salmon elicited an uncomfortable queasiness that often culminated with a sprint to the porcelain throne. Apparently, this type of experience is pretty normal.
Developing an aversion to a specific tastes and smells during pregnancy is an extremely common phenomenon. In fact, between 50–90% of pregnant women worldwide experience some level of food aversion, with the most common aversions being meat, fish, poultry, and eggs. Furthermore, research suggests that food aversions developed during pregnancy are actually novel as opposed to an exaggeration of a pre-existing dislike for a certain food.
Complementing the development of food aversions is the report that dietary changes in pregnant woman are often related to changes in olfaction, or sense of smell. More specifically, some pregnant women experience increased sensitivity to certain odors, and usually in an unpleasant way. This heightened sensitivity is thought to be protective against foods that could pose a problem for mother and baby, such as those that have become rancid.
When I was pregnant, the self-perceived powerfully pungent scent of peas could have probably knocked me over if it was translated into some other physical force. I wish I had a gas mask.
Is there some benefit to morning sickness?
In general, nausea and vomiting are a defense mechanism, acting to protect us from the accidental ingestion of toxins. While morning sickness is likely a very complicated condition that needs further study, a popular explanation suggests that morning sickness is beneficial to both mother and fetus.
Several lines of observations support this idea, formally called the “maternal and embryo protection hypothesis”: (a) peak sensitivity to morning sickness occurs at approximately the same time that embryo development is most susceptible to toxins and chemical agents; and (b) women who experience morning sickness during their pregnancy are less likely to miscarry compared to women who do not experience morning sickness.
In essence, the maternal and embryo protection hypothesis suggests that morning sickness is an adaptive process, contributing to evolutionary success (measured in terms of how many of your genes are present in later generations). However, morning sickness is not found in all societies. One possible explanation for this is that those societies that do not widely experience morning sickness are significantly more likely to have plant-based diets (meats spoil much faster than plants). Another argument against evolutionary adaptation is that morning sickness has been documented only in three other species: domestic dogs, captive rhesus macaques, and captive chimpanzees.
It makes sense that the pregnancy-related nausea and vomiting widely known as morning sickness is a means to help protect mom and baby. It makes sense that women have a mechanism to detect and/or expel toxins and potentially harmful microorganisms if ingested. But the idea that morning sickness is actually a product of evolution is still under debate.
And even as a biologist, if I ever have to go through morning sickness again, the idea that it could be protective won’t really bring me comfort as I am puking up my guts. But, biology is biology and sometimes we just have to deal with it.
Andrews, P. and Whitehead, S. Pregnancy Sickness. American Physiological Society. 1990 February;5: 5-10.
Flaxman, S.M. and Sherman, P.W. Morning Sickness: A mechanism for protecting mother and baby. The Quarterly Review of Biology. 2000 June; 75(2):
Goodwin, TM. Nausea and vomiting of pregnancy: an obstetric syndrome. American Journal Obstetrics and Gynecology. 2002; 185(5): 184-189.
Kich, K.L. Gastrointestinal factors in nausea and vomiting of pregnancy. American Journal Obstetrics and Gynecology. 2002; 185(5): 198-203.
Nordin, S., Broman, D.A., Olofsson, J.K., Wulff, M. A Longitudinal Descriptive Study of Self-reported Abnormal Smell and Taste Perception in Pregnant Women. Chemical Senses. 2004; 29 (5): 391-402
You hold a stick in your hands, one that you’ve just peed on. It foretells a future of sorts, for you. But the magic behind that stick is really all about a biochemical sandwich and a scientific test named ELISA. By Jeanne Garbarino, DXS Editor OH MY GOD OH MY GOD OH MY GOD OH MY GOD OH MY GOD OH MY GOD
Over and over again, that was all I could say. At the same time, I heard my husband on the other side of the bathroom door, in a very panicked voice asking, “Why are you saying oh my god? WHAY ARE YOU SAYING OH MY GOD?!?!”
Though, he really knew why.
The events immediately preceding our synchronous freak out session involved unwrapping a small plastic wand, removing its lilac cap, and subsequently inserting its absorbent tip into my stream of pee. Yes, folks, we are talking about the wand of destiny that is the pregnancy test.
Shortly after that lucky sperm cell unites with the prized product of the ovulatory process, theegg, a woman will immediately begin to experience changes required for growing another human inside of her body. One of the first detectable signs of pregnancy is a surge in a hormone called human chorionic gonadotropin or hCG.
Once the fertilized egg finds a cozy resting place in the wall of the uterus (a process termed implantation), the production of hCG is significantly ramped up. On average, implantation usually takes about 8-10 days for normal, healthy pregnancies. It is around this point on the baby growing timeline that home pregnancy tests can begin to detect the increased presence of hCG.
Chronologically speaking, we have sex, a sperm cell fertilizes an egg cell, said fertilized egg implants into uterus, our bodies up the production of hCG, and we pee on a stick to find out if all of these things really happened. But, exactly how do these little wands of destiny work?
The technology harnessed within the pregnancy test involves a biochemical assay called a “Sandwich ELISA” (ELISA= enzyme-linked immunoabsorbant assay, more on the “sandwich” part in a bit). The general function of an ELISA is to detect (and sometimes quantify) the presence of a substance in a liquid. In the case of a home pregnancy test, the substance is hCG and the liquid part is our urine.
Once pee is applied to the pregnancy test, it travels along the absorbent fibers, reaching defined areas that are coated with molecules, called “capture” antibodies, specifically designed to capture hCG. To help you visualize antibody science, picture a lacrosse stick, except the mesh pocket can only fit one specific type of ball:
Now, back to the sandwich part. On a home pregnancy test, there are three separate zones containing capture antibodies. Using their sharp wit and radical humor, scientists came up with “sandwich” to describe this sort of ELISA as they felt it was analogous to two slices of bread surrounding some delicious filling. Hilarious, right?
Ok, now that you’ve calmed down from laughing so hard, let us get back to the science. The first “slice of bread” is called the reaction zone, the “sandwich filling” is called the test zone, and the “last slice of bread” is called the control zone (see figure 2). Each of these zones is coated with capture antibodies, but differ from each other in how they work.
The antibodies on the reaction zone will capture only hCG and will detach from the strip upon exposure to urine. The test zone also contains capture antibodies that can only bind hCG, except they are securely attached to the absorbent strip, plus, there is an added dye. The control zone contains a general antibody (a lacrosse stick that will fit any ball) plus a dye, and serves to let the frantic user know that the test is functional.
As urine travels up the absorbent strip, it takes with it the reaction zone antibodies. If the urine is obtained from a pregnant woman, the reaction zone antibodies will be bound to hCG molecules found in the pee. When the pee solution reaches the test zone, there are two possible outcomes. If you are pregnant, the hCG/reaction zone antibody complexes will stick to the test zone antibodies and cause the dye to release (sometimes in a little “+” formation). If you are not pregnant, the reaction zone antibodies will just pass on through without saying hello.
The test culminates at the control zone, which is lined with general capture antibodies. Going back to picturing antibodies as lacrosse sticks, you will see that only the shape and size of the mesh pocket varies; the stick part is always the same. The general capture antibodies on the control zone will recognize and bind to the “stick” part of the reaction zone antibodies, and release a dye while doing so. This is how we know that the test worked correctly.
Biochemically speaking, the home pregnancy test is nothing but a soggy antibody sandwich that smells of urine. From a family planning standpoint, however, this technology can impact us in ways beyond belief. But, aside from the potential for the “are you pregnant” window to induce one into a hyperventilated state, the process happening within that handheld chemistry lab is actually quite impressive. In a matter of minutes, we can know if it is ok to go out and party with friends, or if it would be a better choice to stay in and begin to nest – all from the comfort of our own bathrooms. Three cheers for science!
For a cool animation showing how a pregnancy test works, go here. Visit WomensHealth.govfor more information about pregnancy tests. Planned Parenthoodoffers scientifically accurate information about women’s reproductive health. For blogs, check out this list on Babble, and this list on BlogHer.
Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. (1999) Jun 10;340(23):1796-9.
Like the eye of Sauron drawn to the One Ring, one cannot resist looking at the mucus plug.
June 3rd, 2007 fell on a Sunday. I awoke that morning feeling disappointed that I was still pregnant. My due date had come and gone and, honestly, I was sick of being a human incubator. I had enough of the heartburn, involuntary peeing, and the overall beached-whale feeling. The baby in utero was resting comfortably on my sciatic nerve, and I could barely walk. And perhaps even more important was the fact that I just wanted to finally meet the child I had grown from just a few cells!
Feeling like it would never come to be, I slowly waddled into the bathroom and somehow negotiated the tall edge of the bathtub in order to take a shower. As I stood allowing the hot water to pour down my back, I looked down at the giant watermelon growing from my abdomen and literally began to beg. “Little baby, please please PLEASE make your way out today!” Right at that moment, and I kid you not, my cervix released my mucus plug and deposited it into the palm of my hand.
Video of a mucus plug being poked and prodded with tweezers. Watch at your own risk.
Suddenly, I saw the light at the end of the pregnancy tunnel. I excitedly called for my husband. “Jim! You have to come see this!!” He came running in as he was already on edge, given the circumstances. “My mucus plug came out! Do you want to see it?” As much as he tried to resist looking at something that was potentially grotesque (and it was), instinct overrode logic. His actions did not match the words coming out of his mouth, which were along the lines of “hell no!” and, like Sauron responding to the wearing of the ring, his eyes were slowly drawn down to what was gently wobbling in the palm of my hand.
The human eye is poised for setting its gaze upon things that are aesthetically pleasing and the mere mention of the word “mucus” could potentially elicit a queasy feeling in one’s gut. However, mucus plays a significant biological role in our bodies. In general, the mucus serves as a physical barrier against microbial invaders (bacteria, fungi, viruses) and small particulate matter (dust, pollen, allergens of all kinds). Protective mucus membranes line a multitude of surfaces in our bodies, including the digestive tract, the respiratory pathway, and, of course, the female reproductive cavity.
But when it comes to matters of ladybusiness, the function of mucus goes beyond that of a microbial defense system. Produced by specialized cells lining the cervix, which is the neck of the uterus and where the uterus and vagina meet, mucus also plays a role in either facilitating or preventing sperm from traveling beyond the vagina and into the upper reproductive tract.
For instance, cervical mucus becomes thinner around the time of ovulation, providing a more suitable conduit for sperm movement and swimming (presumably toward the egg). Furthermore, some components from this so-called “fertile” cervical mucus actually help prolong the life of sperm cells. Conversely, after the ovulation phase, normal hormonal fluctuations cause cervical mucus to become thicker and more gel-like, acting as a barrier to sperm. This response helps to prepare the uterus for pregnancy if fertilizationhappens.
During pregnancy, a sustained elevation of a hormone called progesteronecauses the mucus-secreting cells in the cervix to produce a much more viscous and elastic mucus, known as the cervical mucus plug. In non-scientific terms, the mucus plug is like the cork that keeps all of the bubbly baby goodness safe from harmful bacteria. It is quite large, often weighing in around 10 g (0.35 oz) and consists mostly of water (>90%) that contains several hundred types of proteins. These proteins do many jobs, including immunological gatekeepers, structural maintenance, regulation of fluid balance, and even cholesterol metabolism (cholesterol is an ever important component of healthy fetal development).
As a woman nears the end of a pregnancy, the cervix releases the mucus plug as it thins out in preparation for birth. Often, the thinning of the cervix can release some blood into the mucus plug, which is why some describe the loss of the mucus plug as a “bloody show.” However, losing the mucus plug is not necessarily an indication that labor is starting. Activities like sex or an internal cervical examination can cause the mucus plug to dislodge. It can fall out hours, days, or even weeks before labor begins. In my case, the loss of my mucus plug was associated with the onset of labor, which is why I have never been so happy to hold something so disgusting in my hand.
Last week, I told the story of my two births, including the loss of my mucus plug, at an event called The Story Collider. I described the mucus plug as “a big hot gelatinous mess.” I pushed it a bit further by providing the following graphic imagery: “Picture a Jell-O jiggler, but instead of brightly colored sugar, it’s made up of bloody snot.” I was pleased with the audience response, which mostly consisted of animated face smooshing accompanied by grossed-out groans and sighs. For the rest of the evening, I heard people call to me from all over the bar by screaming “MUCUS PLUG!!!” Given the importance of the mucus plug during pregnancy (and mucus in general) combined with its comedic potential, its no wonder that it was a hit. Go mucus!
Kamran Moghissi, Otto W. Neuhaus, and Charles S. Stevenson. Composition and properties of human cervical mucus. I. Electrophoretic separation and identification of proteins.. J Clin Invest. 1960 September; 39(9): 1358–1363.
Lee DC, Hassan SS, Romero R, Tarca AL, Bhatti G, Gervasi MT, Caruso JA, Stemmer PM, Kim CJ, Hansen LK, Becher N, Uldbjerg N. Protein profiling underscores immunological functions of uterine cervical mucus plug in human pregnancy.J Proteomics. 2011 May 16;74(6):817-28. Epub 2011 Mar 23.
Ilene K. Gipso. Mucins of the human endocervix. Frontiers in Bioscience 2001 October; 6, d1245-1255.
Merete Hein MD, Erika V. Valore MS, Rikke Bek Helmig MD, PhD, Niels Uldbjerg MD, PhD, Tomas Ganz PhD, MD. Antimicrobial factors in the cervical mucus plug. American Journal of Obstetrics and Gynecology 2002 July Volume 187, Issue 1, 137-144
Naja Becher, Kristina Adams Waldorf, Merete Hein & Niels Uldbjerg. The cervical mucus plug: Structured review of the literature. Acta Obstetricia et Gynecologica. 2009; 88: 502_513
An historic view interpretation of the placenta (source).
She gave me a few minutes to meet my daughter before she reeled me back into a state that was my new reality. “You’re not finished Jeanne. You still need to birth your placenta.” What?!?! More pushing? But I was lucky and the efforts required to bring my placenta ex vivo were minimal.
This is the second placenta my body helped make. OK, so it doesn’t EXACTLY look like meatloaf…
The idea of a placenta, which is the only human organ to completely and temporarily develop after birth, was fascinating. That thing sitting in a rectangular periwinkle bucket was what allowed me to grow another human.. inside of my body! There was no way I was not going to check it out, as well as create a permanent record of its relatively short-lived existence.
My first impression was that it looked like “meatloaf.” Not necessarily a well made meatloaf, but perhaps one that is made by my mother (sorry mom). But, alas, chaos reigned and I wasn’t able to really take a good look. However, for my second birth and hence second placenta, my midwife indulged me with a more detailed look and a mini-lesson.
Baby’s eye view: Where geekling deux spent 39 weeks and 4 days.
Her gloved hands, still wet with my blood and amniotic fluid, slid into the opening that was artificially created with a tool resembling a crocheting needle. She opened the amniotic sac wide so I could get a baby’s eye view of the crimson organ that served as a nutritional trading post between me and my new bundle of joy.
She explained that the word “placenta” comes from from the Greek word plakoeis, which translates to “flat cake” (however, I’m sure if my mom’s meatloaf was more common in ancient Greece, the placenta would be named differently). “It’s one of the defining features of being a mammal,” she explained as I was working on another mammalian trait – getting my baby to nurse for the first time.
That was about all I could mentally digest at the time, but still, more than three years later, the placenta continues to fascinate me, mostly due to the fact that it is responsible for growing new life. It’s a natural topic for this long overdue Pregnancy101post, so let’s dive in!
Development of the placenta
It all starts when a fertilized egg implants itself into the wall of the uterus. But, in order to fully understand how it works, we should start with an overview of the newly formed embryo.
The very early stages of us (and many other things that are alive).
The trophoblast invades the uterus, leading to implantation of the blastocyst.
As soon as a male sperm cell fuses with a female egg cell, fertilization occurs and the cells begin to multiply. But, they remain contained within a tiny sphere. As the cells continue to divide, they are given precise instructions depending on their location within that sphere, and begin to transform into specific cell types. This process, which is called cellular differentiation, actually seals the fate every cell in our body, sort of like how we all have different jobs – some of us are transport things, some of us are involved in policing the neighborhoods, some of us build structures, some of us communicate information, some of us deal with food, some of us get rid of waste, etc. Every cell gets a job (it’s the only example of 100% employment rates!).
Now back to the cells in the fertilized egg. As they start to learn what their specific job will be, the cells within the sphere will start to organize themselves. After about 5 days after fertilization, the sphere of cells becomes something called a blastocyst, which readies itself for implantationinto the wall of the uterus.
The act of implantation is largely due to the cells found on the perimeter of the blastocyst sphere. These cells, collectively known as the trophoblast, release a very important hormone – human chorionic gonadotropin (hCG) – that tells the uterus to prepare for it’s new tenant. (If you recall, hCG is the hormone picked up by pregnancy tests.) Around day 7, the trophoblast cells start to invade the lining of the uterus, and begin to form the placenta. It is at this point that pregnancy officially begins. (Here is a cool video, created by the UNSW Embryology Department, showing the process of implantation.)
Structure of the placenta
Eventually the trophoblast becomes the recognizable organ that is the placenta. Consider the “flat cake” analogy, with the top of the cake being the fetal side (the side that is in contact with the baby), and the bottom of the cake being the maternal side (the side that is in contact with the mother).
Cross section of the placenta: Blood vessels originating from the fetus sit in a pool of maternal blood, which is constantly replenished my maternal arteries and veins. The red represents oxygenated blood, and the blue represents de-oxygenated blood.
Projecting from the center of the fetal side of the placenta are two arteries and one vein, coiled together in a long, rubbery rope, often bluish-grey in color. This umbilical cord serves as the tunnel through which nutrients and waste are shuttled, and essentially serves to plug the baby into the mother’s metabolic processes. At the umbilical cord-placenta nexus, the umbilical cord arteries and vein branch out into a network of blood vessels, which further divide into a tree-like mass of vessels within the placenta.
These tree-like masses originating from the umbilical cord (and thus fetus) sit in a cavity called the intervillous space, and are bathed in nutrient-rich maternal blood. This maternal blood, which provides the fetus with a means for both nutrient delivery and waste elimination, is continually replenished via a network of maternal arteries and veins that feed into the intervillous space. Furthermore, these arteries and veins help to anchor the placenta into the uterine wall. One of the most interesting aspects about the mother-feus relationship is that the blood vessel connection is indirect. This helps to prevent a detrimental immune response, which could lead to immunological rejection of the fetus (sort of like how a transplanted organ can become rejected by the recipient).
Functions of the placenta
Just like a plant needs sunlight, oxygen, and water to grow, a baby needs all sorts of nutrients to develop. And since a baby also produces waste, by nature of it being alive and all, there is an absolute requirement for waste removal. However, because we can’t just give a developing fetus food or a bottle, nor are we able to change diapers in utero, the onus lies completely on the biological mother.
This is where the placenta comes in. Because the fetus is plugged into the circulatory system of the mother via the umbilical cord and placenta, the fetus is provided with necessary nutrients and a mechanism to get rid of all the byproducts of metabolism. Essentially, the placenta acts as a waitress of sorts – providing the food, and cleaning it all up when the fetus is done eating.
But it’s not just about nutrition and waste. The placenta also serves as a hormone factory, making and secreting biological chemicals to help sustain the pregnancy. I mentioned above that the placenta produces hCG, which pretty much serves as a master regulator for pregnancy in that it helps control the production of maternally produced hormones, estrogen and progesterone. It also helps to suppress the mother’s immunological response to the placenta (along with other factors), which cloaks the growing baby, thereby hiding it from being viewed as a “foreign” invader (like a virus or bacteria).
Another hormone produced by the placenta is human placental lactogen (hPL), which tells the mother to increase her mammary tissue. This helps mom prepare for nursing her baby once it’s born, and is the primary reason why our boobs tend to get bigger when we are pregnant. (Yay for big boobies, but my question is, what the hell transforms our rear ends into giant double cheeseburgers, and what biological purpose does that serve?? But I digress…)
Despite the fact that the mother’s circulatory system remains separate from the baby’s circulatory system, there are a clear mixing of metabolic products (nutrients, waste, hormones, etc). In essence, if it is in mom’s blood stream, it will very likely pass into baby’s blood stream. This is the very reason that pregnant mothers are strongly advised to stay away from cigarettes, drugs, alcohol, and other toxic chemicals, all of which can easily pass through the placental barrier lying between mother and fetus. When moms do not heed this warning, the consequences can be devastating to the developing fetus, potentially leading to birth defects or even miscarriage.
There are also situations that could compromise the functions of the placenta – restriction of blood supply, loss of placental tissue, muted placental growth, just to name a few – reducing the chances of getting and/or staying pregnant. This placental insufficiency is generally accompanied by slow growth of the uterus, low rate of weight gain, and most importantly, reduced fetal growth.
And it’s not just the growth of the placenta that is important – where the placenta attaches to the uterus is also very important. When the placenta grows on top of the opening of the birth canal, the chances for a normal, vaginal birth are obliterated. This condition, known as placenta previa, is actually quite dangerous and can cuase severe bleeding in the third trimester. 0.5% of all women experience this, and it is one of the true medical conditions that absolutely requires a C-section.
Then, there is the issue of attachment. If the placenta doesn’t attach well to the uterus, it could end up peeling away from the uterine wall, which can cause vaginal bleeding, as well as deprive the baby from nutrient delivery and waste disposal. This abruption of the placenta is complicated by the use of drugs, smoking, blood clotting disorders, high blood pressure, or if the mother has diabetes or a history of placental abruption.
Conversely, there are times when the blood vessels originating from the placenta implant too deeply into the uterus, which can lead to a placenta accreta. If this occurs, the mother generally delivers via C-section, followed by a complete hysterectomy.
Cultural norms and the placenta
There are many instances where the placenta plays a huge role in the culture of a society. For instance, both the Maori people of New Zealand and the Navajopeople of Southwestern US will bury the placenta. There is also some folklore associated with the placenta, and several societies believe that it is alive, pehaps serving as a friend for the baby. But the tradition that seems to be making it’s way into the granola culture of the US is one that can be traced back to traditional Chinese practices: eating the placenta.
Placentophagy, or eating one’s own placenta, is very common among a variety of mammalian species. Biologically speaking, it is thought that animals that eat their own placenta do so to hide fresh births from predators, thereby increasing the chances of their babies’ survival. Others have suggested that eating the nutrient-rich placenta helps mothers to recover after giving birth.
However, these days, a growing number of new mothers are opting to ingest that which left their own body (likely) through their own vaginas. And they are doing so though a very expensive process involving dehydrating and encapsulating placental tissue.
Why would one go through this process? The claims are that placentophagy will help ward of post partum depression, increase the supply of milk in a lactating mother, and even slow down the ageing process. But, alas, these are some pretty bold claims that are substantiated only by anecdata, and not actual science (see this).
So, even though my placentas looked like meatloaf, there was no way I was eating them. If you are considering this, I’d approach the issue with great skepticism. There are many a people who will take advantage of maternal vulnerabilities in the name of cold hard cash. And, always remember, if the claims sound to good to be true, they probably are!
Thanks for tuning into this issue of Pregnancy101, and enjoy this hat, and a video!
Human ovum (egg). The zona pellucida is a thick clear girdle surrounded by the cells of the corona radiata (radiant crown). Via Wikimedia Commons.
It was September of 2006. Due to certain events taking place on a certain evening after a certain bottle (or two) of wine, my body was transformed into a human incubator. While I will not describe the events leading up to that very moment, I will dissect the way in which we propagate our species through a magnificent process called fertilization.
During the fertilization play, there are two stars: the sperm cell and the egg cell. The sperm cell hails from a male and is the end product of a series of developmental stages occurring in the testes. The egg cell (or ovum), which is produced by a female, is the largest cell in the human body and becomes a fertilizable entity as a result of the ovulatory process. But to truly understand what is happening at the moment of fertilization, it is important to know more about the cells from which all human life is derived.
Act I: Of sperm and eggs
A sperm cell is described as having a “head” section and a “tail” section. The head, which is shaped like a flattened oval, contains most of the cellular components, including DNA. The head also contains an important structure called an acrosome, which is basically a sac containing enzymes that will help the sperm fuse with an egg (more about the acrosome below). The role of the tail portion of sperm is to act as a propeller, allowing these cells to “swim.” At the top of the tail, near where it meets the head, are a ton of tiny structures called mitochondria. These kidney-shaped components are the powerhouses of all cells, and they generate the energy required for the sperm tail to move the sperm toward its target: the egg.
The egg is a spherical cell containing the usual components, including DNA and mitochondria. However, it differs from other human cells thanks to the presence of a protective shell called the zona pellucida. The egg cell also contains millions of tiny sacs, termed cortical granules, that serve a similar function to the acrosome in sperm cells (more on the granules below).
Act II: A sperm cell’s journey to the center of the universefemale reproductive system
Given the cyclical nature of the female menstrual cycle, the window for fertilization during each cycle is finite. However, the precise number of days per month a women is fertile remains unclear. On the low end, the window of opportunity lasts for an estimated two days, based on the survival time of the sperm and egg. On the high end, the World Health Organization estimates a fertility window of 10 days. Somewhere in the middle lies a study published in the New England Journal of Medicine, which suggests that six is the magic number of days.
Assuming the fertility window is open, getting pregnant depends on a sperm cell making it to where the egg is located. Achieving that goal is not an easy feat. To help overcome the odds, we have evolved a number of biological tactics. For instance, the volume of a typical male human ejaculate is about a half-teaspoon or more and is estimated to contain about 300 million sperm cells. To become fully active, sperm cells require modification. The acidic environment of the vagina helps with that modification, allowing sperm to gain what is called hyperactive motility, in which its whip-like tail motors it along toward the egg.
Once active, sperm cells begin their long journey through the female reproductive system. To help guide the way, the cells around the female egg emit a chemical substance that attracts sperm cells. The orientation toward these chemicals is called chemotaxis and helps the sperm cells swim in the right direction (after all, they don’t have eyes). Furthermore, sperm get a little extra boost by the contraction of the muscles lining the female reproductive tract, which aid in pushing the little guys along. But, despite all of these efforts, sperm cell death rates are quite high, and only about 200 sperm cells actually make it to the oviduct (also called the fallopian tube), where the egg awaits.
Act III: Egg marks the spot
With the target in sight, the sperm cells make a beeline for the egg. However, for successful fertilization, only a single sperm cell can fuse with the egg. If an egg fuses with more than one sperm, the outcome can be anything from a failure of fertilization to the development of an embryo and fetus, known as a partial hydatidiform mole, that has a complete extra set of chromosomes and will not survive. Luckily, the egg has ways to help ensure only one sperm fuses with it.
When it reaches the egg, the sperm cell attaches to the surface of the zona pellucida, a protective shell for the egg. For the sperm to fuse with the egg, it must first break through this shell. Enter the sperm cell’s acrosome, which acts as an enzymatic drill. This “drilling,” in combination with the propeller movement of the sperm’s tail, helps to create a hole so that the sperm cell can access the juicy bits of the egg.
This breach of the zona pellucida and fusion of the sperm and egg sets off a rapid cascade of events to block other sperm cells from penetrating the egg’s protective shell. The first response is a shift in the charge of the egg’s cell membrane from negative to positive. This change in charge creates a sort of electrical force field, repelling other sperm cells.
Though this response is lightning fast, it is a temporary measure. A more permanent solution involves the cortical granuleswithin the egg. These tiny sacs release their contents, causing the zona pellucida to harden like the setting of concrete. In effect, the egg–sperm fusion induces the egg to construct a virtually impenetrable wall. Left outside in the cold, the other, unsuccessful sperm cells die within 48 hours.
Now that the sperm–egg fusion has gone down, the egg start the maturation required for embryo-fetal development. The fertilized egg, now called a zygote, begins its journey into the womb and immediately begins round after round of cell division, over a few weeks resulting in a multicellular organism with a heart, lungs, brain, blood, bones, muscles, and hair. It’s an amazing phenomenon that I’m honored to have experienced (although I didn’t know I was until several weeks later).
The Afterword: A note on genetics
A normal human cell that is not a sperm or an egg will contain 23 pairs of chromosomes, for a total of 46 chromosomes. Any deviation from this number of chromosomes will lead to developmental misfires that in most cases results in a non-viable embryo. However, in some instances, a deviation from 46 chromosomes allows for fetal development and birth. The most well-known example is Trisomy 21(having three copies of the 21st chromosome per cell instead of two), also called Down’s Syndrome.
The egg and sperm cells are unlike any other cell in our body. They’re special enough to have a special name, gametes, and they each contain one set of chromosomes, or 23 chromosomes. Because they have half the typical number per cell, when the egg and sperm cell fuse, the resulting zygote contains the typical chromosome number of 46. Now you know how we get half of our genes from our father (who made the sperm cell) and half from our mother (who made the egg cell). Did I just put in your head an image of your parents having sex? It’s the birds and the bees, folks—it applies to everyone!
All text and art except as otherwise noted: Jeanne Garbarino, Double X Science Editor
World Health Organization. “A prospective multicentre trial of the ovulation method of natural family planning. III. Characteristics of the menstrual cycle and of the fertile phase,” Fertil Steril(1983);40:773-778
Allen J. Wilcox, et al. “Timing of Sexual Intercourse in Relation to Ovulation — Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby,” New England Journal of Medicine, (1995); 333:1517-1521
Poland ML, Moghisse KS, Giblin PT, Ager JW,Olson JM. “Variation of semen measures within normal men,” Fertil Steril (1985);44:396-400
Alberts B, Johnson A, Lewis J, et al. “Fertilization,” Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002.
[Editor's note: We are pleased to be able to run this post by Dr. Kate Clancy that first appeared at Clancy's Scientific American blog, the wonderful Context and Variation. Clancy is an Assistant Professor of Anthropology at the University of Illinois. She studies the evolutionary medicine of women’s reproductive physiology, and blogs about her field, the evolution of human behavior and issues for women in science. You can follow her on Twitter--which we strongly recommend, particularly if you're interested in human behavior, evolutionary medicine, and ladybusiness--@KateClancy.]
Over the course of my training to become a biological anthropologist with a specialty in women’s reproductive ecology and life history theory, or ladybusiness expert, I have learned a lot about miscarriage. Only it wasn’t miscarriage, it was spontaneous abortion. Except that some didn’t like the term spontaneous abortion and used intrauterine mortality (Wood, 1994). Or fetal loss. Fetal loss is probably the most common.
There is also pregnancy loss (Holman and Wood, 2001). You can use that term, too. Oh, or aContinue reading →
In the first case-based class of medical school, students are asked to answer a virtual patient’s question about the development of the fetus. These students are smart and they know all about betaHcG and are anxious to showcase their knowledge of the menstrual cycle with fluctuating levels of various hormones (FSH, progesterone, etc.). Yet one question brings confusion, “How pregnant is this woman?” The related question, “When does pregnancy start?” leaves the students flummoxed. Is it at conception? But how do you know when that happens? Or does implantation make more sense? It’s a great example of how detailed facts need the larger context.
The usual dating is gestational age, based on the first day of your last menstrual period. However, you can also date a pregnancy with embryological age, starting at conception.
How you date a pregnancy can depend on your perspective. My very general guideline:
Pregnant woman is the focus = gestational age (e.g., obstetricians) 1
Focus on embryological/fetal development = embryological age (e.g., developmental biologist) 2
But why are there two types of dates? We might need a bit of a primer on the menstrual cycle and how it relates to pregnancy.
Implantation happens between days 20 and 22. Pregnancy is often detected after the first missed period.
This graphic is intentionally simple, removing all the hormones and other fun stuff (Ed: which you can find here). You’ll note that it says approximately day 14 and day 28. In textbooks, we often see that women have 28-day cycles and everything has a nice schedule. However, women are not textbooks and sometimes have shorter or longer cycles and/or have ovulation at slightly different times. Therefore, knowing when fertilization and conception happen can be a bit tricky. An obvious marker is the first day of the last menstrual period (LMP). Why the last day? Well, another variable is the length of menses but everyone has a first day so to be consistent, that is the marker used.
We generally use gestational age when discussing pregnancy. So when someone says that they are 8 weeks pregnant, they mean it has been 8 weeks since the first day of the LMP (last menstrual period).
But that means that the first two weeks of pregnancy has nothing happening. If you are concerned about development, you don’t start counting at week 3 but start at the time of fertilization, two weeks later. Therefore, the embryological age is generally two weeks later.
But remember, we have essentially picked gestational age as the convention for discussing pregnancy dates. If there are markers in development to suggest that the embryological age is different (for example, the fetus is 12 weeks, not 13 weeks), the gestational age is often reported to the mother. In our example, the dating would be changed to 14 weeks.
Due to the difference in these dates, we see confusion beyond medical students thinking about this for the first time. It was recently reported that Arizona had changed its abortion law to be the most restrictive – but it hadn’t. It had just joined other states in making the limit 20 weeks gestational age. Remember, this is the accepted convention for pregnancy dating – but many articles picked up on that initial two weeks of nothingness in gestational age and confused it with embryological age. Was this an example of details without understanding of the greater context?
Synonyms include developmental, conception, and fetal age. ↩
Opinions expressed in this piece are those of the author and do not necessarily reflect or conflict with the opinions of DXS editors or contributors.
Dr. Catherine Anderson is a Clinical Instructor for the Faculties of Medicine and Dentistry for UBC in Vancouver, Canada. She also leads the Future Science Leaders program, helping teens excel in science and technology. She received her PhD in Medical Genetics and has spent the last 10 years helping people understand the biological sciences: the information and the impact on our lives. You can follow her on Twitter @genegeek.