The study is published in the New England Journal of Medicine and is the work of scientists in Denmark and the US.
Abortion pills, also called medical abortions, are being used more and more by women to terminate unwanted pregnancies during the first trimester but there is little evidence of how this affects the safety of future pregnancies.
However, surgical abortion is still preferred by most women who find themselves with an unwanted pregnancy that they wish to terminate.
In the surgical method the woman is admitted to hospital and the procedure is performed using a vacuum pump or syringe to remove the fetus from the womb. In this method there is very little risk that embryonic material is left in the womb.
In the medical or pill based method, the woman takes one tablet of mifespristone (the drug's experimental name was RU-486 and many people still use this term) and then four or so misoprostol pills a day or two later.
The first pill, the mifepristone, is a synthetic steroid that destabilizes the tissue that joins the embryo to the uterus. The pills taken later, the misoprostol, cause the uterus to contract and expel the fetus. The procedure is different in different countries.
However, there is a slight risk with the medical method that embryonic material can remain in the womb, and there are mixed views about whether the woman should have an exam to make sure the fetus has been properly expelled. In Europe for example, women must be kept under medical observation, whereas this is not required in the US.
In the US, the Food and Drug Administration (FDA) approved mifepristone for use in medical abortions in 2000. It is only approved for use in the first 49 days of gestation.
In the US, between 2000 and 2004, some 360,000 women used the mifepristone and misoprostol abortion method to carry out abortions.
The medical method is often chosen because the woman can take the pill at home, in private, or during a consultation with her doctor. In the US the FDA approval requires that the woman have counselling first. The pills can be prescribed by any doctor and the procedure is perceived as more straightforward than the surgical method.
In this study, Dr Jun Zhang from the Epidemiology Branch of the National Institute of Child Health and Human Development, National Institutes of Health, in Bethesda, Maryland, US, and colleagues analysed nationwide data of all women in Denmark who had undergone abortions for non medical reasons between 1999 and 2004. And they also obtained data on subsequent pregnancies from national registers.
They then compared the risk of ectopic pregnancy, spontaneous abortion, preterm birth (at under 37 weeks of gestation), and low birth weight (under 2.5 kg, or 5.5 pounds) in 2,710 women who had had medical abortions during the first trimester of pregnancy with 9,104 who had had surgical abortions in the first trimester.
The results showed that among the 11,814 post abortion pregnancies in both groups of women there were:
- 274 ectopic pregnancies (2.4 per cent in the medical abortion group and 2.3 per cent in the surgical abortion group).
- 1426 spontaneous abortions (12.2 per cent and 12.7 per cent).
- 552 preterm births (5.4 per cent and 6.7 per cent).
- 478 births with low birth weight (4.0 per cent and 5.1 per cent).
Zhang and colleagues concluded that:
"We found no evidence that a previous medical abortion, as compared with a previous surgical abortion, increases the risk of spontaneous abortion, ectopic pregnancy, preterm birth, or low birth weight."
In an accompanying Journal Watch article, Dr Robert W. Rebar, comments that:
"As long as induced abortion is available, it will be used by some women who fail to use contraception or have contraceptive failures and do not desire pregnancy. This study indicates that the risks for subsequent adverse pregnancy outcomes are not appreciably different for medical and surgical abortion."
"Medical Abortion and the Risk of Subsequent Adverse Pregnancy Outcomes."
Jasveer Virk, Jun Zhang, and Jørn Olsen.
Volume 357, 648-653, August 16, 2007, Number 7
Written by: Catharine Paddock