Surgical methods used in a common form of abortion or to clear the womb after a spontaneous miscarriage appears to significantly increase the risk of a later preterm birth, say researchers at Thomas Jefferson University who analyzed 36 studies that enrolled more than 1 million women.
The additional risk is small -- .7 percent -- when compared to women who have not had the surgery or who may have used medical means to clear their uterus. "But, when considered in the light of hundreds of thousands of women who have had such surgery, this is an unnecessary risk to take," says the study's senior author, Vincenzo Berghella, M.D., Director of Maternal Fetal Medicine at Thomas Jefferson University Hospital, and Professor of Obstetrics and Gynecology at Sidney Kimmel Medical College at Thomas Jefferson University.
"This is not a study that suggests abortions per se are risky and shouldn't be done. What we are saying is that women should be given a choice between a surgical and a medical procedure, and should also be informed about the potential risk to subsequent pregnancy," Dr. Berghella says.
But he added that due to the limitations of some of the studies included in this meta-analysis, "it is difficult to definitively recommend that surgical abortion should be avoided and that medical methods should be preferentially offered."
Their study, published in the American Journal of Obstetrics & Gynecology, was a meta-analysis aimed at determining if any link existed between surgical or medical means to clear the uterus and subsequent pregnancies that do not achieve full terms. One reason to conduct the study is that the incidence of preterm births has been rising, and falling, in parallel to popularity of abortion, the vast majority of which, until late, have been surgical.
Surgical evacuation of the uterus mechanically stretches the cervix, and does so quickly, Dr. Berghella says. "In normal birth, dilation of the cervix occurs slowly over a period of many hours. Mechanically stretching the cervix, however, may result in permanent physical injury to the cervix." Resulting scar tissue, for example, could increase the probability of faulty placental implantation in the womb, and could increase risk for infectious diseases, he adds.
In contrast, medical abortions involve use of one or two drugs -- misoprostol and mifepristone, known as RU-486 -- designed to mirror the process of a spontaneous abortion. Mifepristone, which is approved in the U.S. for aborting pregnancies up to 49 weeks, softens the uterus over time and misoprostol induces contractions. The combination is said to be effective in terminating 95 percent of pregnancies, and in finishing spontaneous abortions where some of the tissue supporting the pregnancy needs to be removed.
Abortions are increasingly being conducted using the medical approach, which requires several days to conduct and likely two visits to a provider, Dr. Berghella says.
Included in the meta-analysis were 31 studies that reported prior abortions in women who later delivered another child, and five studies that focused on women, who later became pregnant, who spontaneously aborted a prior pregnancy but needed either surgery or medicine to complete the miscarriage.
The goal was to look at women who subsequently delivered a child before the 37th week of pregnancy. "The issue is important because preterm birth is the number one cause of perinatal mortality in many countries, including the U.S.," Dr. Berghella says.
• Considering all 1,047,683 women enrolled in the 36 studies, women with a history of uterine evacuation had a significantly higher risk of preterm birth (5.7 percent) compared to a control group of women who did not have either a surgical or medical procedure (5 percent); had babies that were of low birth weight (7.3 percent versus 5.9 percent), and infants that were small for their gestational age (10.2 percent) versus 9.0 percent).
• Of the 31 studies that reported prior abortions, 28 included 913,297 women who had surgery, and three included 10,253 women given medical abortions. Women with prior surgical abortion had a significantly higher risk of preterm birth (5.4 percent versus 4.4 percent for the control population), low birth weight babies (7.3 percent versus 5.9 percent), and small gestational age infants (10.2 percent versus 9 percent).
• In the three studies that looked at medical abortions, the risk of preterm birth was the same as in the control group.
• In the five studies of 124,133 women that looked at spontaneous miscarriages, those women who had a surgical procedure to clear the uterus had a higher risk of subsequent preterm births compared to the control group (9.4 percent versus 8.6 percent).
"These data -- the most comprehensive look at the issue to date -- find that prior surgical uterine evacuation may be an independent risk factor for preterm birth," says Berghella. "The findings warrant caution in the use of these surgical techniques, and should encourage the development of safer surgery as well as use of medical methods."
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