Thursday, December 20, 2007
Abortions increase the risk of low birth weight in future pregnancies by a factor of three, and of premature birth by a factor of two, according to the largest U.S. study of its kind. The study is hardly perfect; the data is more than 40 years old and doesn't distinguish between medical abortions and "spontaneous abortions," better known as miscarriages. Yet the report, published today in the Journal of Epidemiology and Community Health (JECH), shows one of the strongest links yet between miscarriage or abortion on premature birth and low birth weight — major risk factors for infant death or sickness.
The Guttmacher Institute has issued the following comments on the study:
Comments on Brown JS, Adera T and Masho SW, “Previous abortion and the risk of low birth weight and preterm births,” Journal of Epidemiology and Community Health, 2008, 62: 16–22
Prepared by the Guttmacher Institute, December 2007
The 2008 study by Brown, Adera and Masho purports to show a causal connection between abortion and subsequent premature births. In reality, the study does not even show an association between induced abortion and premature birth. The study suffers from several fundamental flaws:
1. The study does not distinguish between spontaneous abortions (i.e., miscarriages) and induced abortions (commonly known as “abortions”).
It is well known that miscarriages are associated with low birthweight and prematurity because the physiological conditions responsible for some miscarriages can also cause prematurity and low birthweight. Thus, a study that does not distinguish spontaneous from induced abortion says nothing about the effect of induced abortion. (Although the term “spontaneous abortion” as a synonym for miscarriage is well understood in the medical community, the general public equates “abortion” with induced abortion, a fact that makes this study’s title and content prone to misinterpretation.)
2. Abortion is dramatically underreported by women in surveys.
Even today, many women do not report their prior induced abortions, and even fewer would have done so at the time these data were collected (1959–1966), when abortion was generally illegal. We can tell that abortion was underreported in this study because the number of miscarriages plus abortions reported in the study was about 13% of the number of births; this is fewer than the number of miscarriages alone that one would expect given the number of births that occurred. Therefore, it is likely that very few of the “abortions” reported in the study were in fact induced abortions.
3. The Brown study looks at preterm births that occurred more than 40 years ago, before induced abortion was legal nationwide.
At that time, most abortions were performed by dilation and curettage; even if these abortions (many illegal) were associated with later reproductive problems, this has no bearing on the effect of induced abortions as performed today, most of which are performed by vacuum aspiration. Several reviews of the available scientific literature affirm that vacuum aspiration — the modern method most commonly used during first-trimester abortions — poses virtually no long-term risks of future fertility-related problems, such as infertility, ectopic pregnancy, spontaneous abortion or congenital malformation.
• In 2006, the Institute of Medicine of the National Academies released a comprehensive, 772-page report, Preterm Birth: Causes, Consequences, and Prevention. Induced abortion is not mentioned anywhere in the body of the report, and only appears once in an appendix table of factors that have been suggested to be associated with preterm birth.
• The preterm birth rate (for singleton births only) rose 13% between 1990 and 2005. In contrast, the abortion rate has declined since 1980, most rapidly from 1990–1996. If abortion were an important risk factor for preterm birth, we might expect to see the preterm birth rate decline as the rate of abortion declined, but there is no evidence of this.