In a finding likely to reignite debate over proposed new limits on abortion, British researchers have found that years ago, women who terminated a pregnancy increased their risk of giving birth prematurely in subsequent pregnancies, but that with modern procedures the danger has all but vanished.
The researchers suggest the shift is the result of a growing use of oral medication to induce or aid in abortion, and a decline in surgical abortions that may injure a woman’s cervix.
The study looked at 732,719 first births by women in Scotland between 1980 and 2008 and found that during the early 1980s, women who’d had one abortion or more had a higher rate of preterm births during later pregnancies. But the researchers documented a steady drop in that risk over the next 15 to 20 years, and concluded that by the year 2000, Scottish women with a history of abortion were no longer more likely to give birth before 37 weeks’ gestation, the widely accepted definition of prematurity.
The new research, published Tuesday in the open-access journal PLoS Medicine, comes as a growing number of states in the U.S. move to place new restrictions on so-called medical abortions, which use a combination of two medications — mifepristone (long referred to as RU-486) and misoprostol — to terminate pregnancy during the first trimester.
Those measures have largely sought to restrict the circumstances for such medications’ use, making medical abortions less accessible in states such as Oklahoma, Texas, Ohio and North Dakota. Proponents argue that the measures are necessary to improve patients’ safety.
“The take-home message from this is that abortion as it’s being currently provided is very safe and not associated with the risk of subsequent preterm birth,” said Dr. Dan Grossman, a professor of obstetrics and gynecology at UC San Francisco who was not involved in the study.
Grossman, vice president for research at the nonprofit IBIS Reproductive Health in Oakland, added that although the study did not demonstrate that the downturn in preterm births was related to the increasing use of medical abortions, it was “hypothesis-generating.”
In the U.S., about 1 in 4 abortions is performed with the two-medication regimen, which was approved by the Food and Drug Administration in 2000 after more than a decade of controversy. In Scotland, where the use of mifepristone and misoprostol to end a pregnancy has not been controversial, medical abortions represented 68% of abortions performed in 2008. That is a sharp rise from 1992, when such procedures accounted for 18% of abortions.
The study was hailed by abortion rights groups, which cited it as evidence that restricting women’s access to newer medication-based abortion procedures would not make them safer.
“Women have been using medication abortion safely for more than a decade,” said Eric Ferrero, a spokesman at Planned Parenthood Federation of America. “If a woman follows the instructions provided by her doctor, there are no risks to her future fertility or pregnancy.”
At the same time, the new study offers support for a claim that has been controversial among U.S. abortion providers — that a history of abortion may, in some cases, put a woman at greater danger of giving birth prematurely in subsequent pregnancies.
Among the Scottish women who gave birth to their first child between 1980 and 1983, those who had aborted an earlier pregnancy boosted their risk of giving birth prematurely by 18%. Women who had undergone more than one abortion raised their risk of subsequent premature birth an additional 18% for each procedure. And researchers found that for those with a history of three or more abortions, the risks of neonatal death were nearly tripled.
The research did not look at the specific methods of abortion used by the individual women in the study, but the British researchers surmised that the mechanical dilation of a woman’s cervix in advance of surgical abortion was more likely to result in cervical trauma that could compromise her ability to carry a subsequent pregnancy to term.
In medical abortions, synthetic hormones are used to mimic natural agents that soften and dilate the cervix in preparation for childbirth. That approach appears less likely to cause injury, the authors of the study speculated.
Past studies have found conflicting evidence of a link between abortion and subsequent preterm birth — a fact that has dissuaded the American Congress of Obstetricians and Gynecologists from recommending that women seeking abortion be warned of any increased risk of prematurity in later pregnancies.
The physicians group’s silence has been roundly criticized by the American Assn. of Pro-Life Obstetricians and Gynecologists, based in Eau Claire, Mich.
“The existing medical literature strongly confirms that induced abortion may play a significant role” in subsequent premature births, the group wrote in a position paper on its website.
In 2011, the Royal College of Obstetricians and Gynaecologists recommended that British physicians advise a woman wishing to terminate a pregnancy that doing so would raise her risk of subsequent premature birth. That guideline followed a 2009 analysis of existing research that found that following an abortion a woman carrying a pregnancy had a 36% greater risk of giving birth prematurely and a 35% greater risk of having a low-birth-weight child — risks that more than doubled with a history of more than one abortion.
Citing their findings, the researchers wrote that the current recommendations guiding British physicians “should be reconsidered.”
The study authors added that their findings should guide abortion practice in ways that could reduce the toll of prematurity, which affects nearly 1 in 10 babies born around the world, according to the World Health Organization. Complications of preterm birth claim the lives of a million babies annually and can cause lifelong disability, including cerebral palsy, sensory deficits, learning problems and respiratory illnesses.
“Modernizing methods of abortion within a region where purely surgical methods are widespread may significantly reduce the subsequent burden of morbidity and mortality related to preterm birth,” the authors of the PLoS Medicine article wrote.