What once was a link has now vanished.
by Tara Haelle
A positive pregnancy test.
Does having an abortion increase a woman’s risk of later having a preterm birth? A study published last week looked at this lingering open question related to possible long-term effects of abortion, with results that shift the current consensus.
Although political and social debates about abortion and abortion-related legislation have flared across the country, science frequently takes a back seat amidst the shouting. Whether it’s inaccurate characterizations of fetal pain or the constant resurfacing of long-disproved myths linking abortion and breast cancer risk, the evidence we do have about abortion and abortion-related issues often doesn’t get heard.
Yet data can and should help guide policy on abortion, as with any other issue, but particularly one about which we know some things to be true, others to be false, and still others to be awaiting a verdict. Science is a process, and sometimes new findings will rewrite conclusions, whether because of better data, technological or medical advances, or improved knowledge. All three underlie the latest findings.
The investigators (PLOS Medicine open access paper available here) in this recent study evaluated a Scottish cohort and found that the risk of a preterm birth does not appear to be associated with having had a past abortion — or at least, it’s not associated any more.
Many previous studies have found a small increase in the odds of having a preterm birth among women who previously had an abortion. A meta-analysis published as recently as 2009 found a small increase in the risk of preterm birth for this population of women. But more than 98% of the births included in that analysis occurred before the year 2000. Meanwhile, medical understanding and practices, including abortion procedures, have changed.
In this latest study, Clare Oliver-Williams and her colleagues analyzed a cohort of 732,719 first births occurring at 24 weeks of gestation or later in Scotland from 1980 to 2008. After adjusting the analysis for maternal features that might muddle any links, the researchers found that for the total population, the odds of a preterm birth were about 12% greater among women who had a previous abortion compared to those who had not.
The increase was small but statistically significant. However, when the authors analyzed the data by year of delivery, they found something interesting: The link between abortion and preterm birth was strongest from 1980 to 1983, when the odds of preterm birth were 32% higher. The increased risk of a preterm birth among women who had undergone a previous abortion then declined gradually from 1984 through 1999. By 2000, it had vanished, and through 2008, it never returned.
Having had an abortion thus was once a modest but real risk factor for preterm birth in Scotland in the 1980s and 1990s. By 2000, though, it was no longer a risk factor. What changed? The way abortions were administered, this study suggests. From 1992 to 2008, the researchers write, the percentage of women receiving surgical abortions without a cervical pre-treatment declined from 31% to 0.4%. In those earlier years, almost a third of women getting abortions had only mechanical cervical dilation for the curettage. As researchers learned more about the role and biology of the cervix during childbirth, the importance of chemically ripening the cervix became more evident. By 2008, just about every woman getting an abortion was treated first with artificial prostaglandins to soften and dilate the cervix.
“The most plausible explanation for these observations,” the authors wrote, “is that surgical termination of pregnancy without cervical pre-treatment is causally associated with the subsequent risk of spontaneous preterm birth and that declining use of this procedure led to the disappearance of the association between prior abortion and preterm birth form 2000 onwards.”
Also during the same time frame, medical abortions — non-surgical abortions carried out with abortifacient pharmaceuticals such as mifepristone — increased from 18% to 68%. So, fewer women were having surgical abortions, and those who were benefited from advances in medical practice and knowledge that made cervical damage from an abortion less likely. However, even when the researchers set aside the medical abortions and looked exclusively at surgical abortions from 2000 onward, they still found no increased risk of preterm birth. That left the use of cervical pre-treatment as the most reasonable explanation for the vanishing association.
In the U.S., surgical abortions still dominate, comprising 82% of the legal abortions performed in 2009, the most recent year for which reliable data are available, compared to 16.5% medical abortions. However, a pre-cervical treatment during abortions is standard in the U.S., so it’s reasonable to speculate that the current method for performing surgical abortions in the U.S. may have eliminated the previous link to preterm birth.
The study is important on two counts: First, the link between prior abortions and preterm first births has diminished to non-significance in at least one population. Second, a probable explanation based on changes in medical practice has been identified, and these updated practices are wide use in other developed countries where abortions are legally performed.
What will be interesting to see is whether the propaganda surrounding abortion will incorporate an update on this no-longer-existent link. Other facts about abortion don’t seem to make it into such updates. For example, the myth that having an abortion increases a woman’s risk of developing breast cancer remains persistent in pseudoscientific, agenda-driven corners of the Internet, even though the National Cancer Institute at the National Institutes of Health has clarified that no such link actually exists.
Similarly, a 2008 task force report from the American Psychological Association determined, based on a review of all literature published since 1989, “that among adult women who have an unplanned pregnancy, the relative risk of mental health problems is no greater if they have a single elective first-trimester abortion than if they deliver that pregnancy.” Despite the lack of evidence, anti-abortion advocacy groups continue to promote the myth of a fictional “post-abortion syndrome.”
In reality, the risks associated with carrying a pregnancy to term, ranging from preeclampsia and gestational diabetes to serious and life-threatening complications, exceed the health risks related to abortions. Fewer than 0.3% of abortions involve complications that require hospitalization. Comparatively, anywhere from 20% to 90% of pregnancies carried to term involve complications, depending on how a complication is defined.
While the U.S. Centers for Disease Control and Prevention reports that approximately 650 women a year still die from pregnancy-related or childbirth-related conditions, only 12 deaths from abortion procedures were reported in 2008, the most recent year for which data are available. Those are legal abortions, of course, because the figures could be much higher for illegal abortions in areas where legal abortion is not available, given that lack of access to abortion does nothing to affect the actual rate of abortion. In 2007, only six deaths were reported. A study published last year found that the rate of maternal deaths from pregnancy/childbirth in the U.S. is approximately 8.8 deaths per 100,000 live births for 1998 through 2005, compared to 0.6 deaths per 100,000 abortions during that time period.
In short, if a decision about whether to have an abortion or carry a child to term were made solely on the basis of data about the risks and benefits to a woman’s health, the data leave no question about which choice is safer. This new study now clarifies that advances in medical understanding and changes in medical practice have effaced another risk factor related to abortion. Certainly health is not the only consideration in these debates and discussions about abortion-related policy. Countless other factors will enter into any decision a woman makes about pregnancy, but the facts about what we do know should not be ignored or misrepresented.
Also at Double X Science