Women who are informed know of abortion’s link to breast cancer, to infertility, and to future ectopic pregnancy. Now there is strong evidence that an abortion substantially increases the likelihood of subsequent premature births.

“Induced Abortion and Risk of Later Premature Births” appears in the Summer 2003 edition of the Journal of American Physicians and Surgeons. The study, authored by Brent Rooney and Byron Calhoun, M.D., points out that at least 49 studies conducted between 1966 and March 2003 have shown a statistically significant increase in premature births or “surrogates” such as low birth weights in women who have had prior induced abortions.

In 36 years of studies tracked by Rooney and Calhoun, only eight studies failed to show a statistically significant increase, and in many cases this was simply because the sample sizes were too small. There were no studies found in recognized medical journals during this period showing a decreased risk of subsequent prematurity following an abortion.

The report offered some astounding results. A 1993 Australian study of 121,305 total births found the risk of an extremely premature birth (20-27 weeks gestational age) to be 60% higher for women with one previous abortion, 150% higher for those with two abortions, and 460% higher for women having three or more previous induced abortions — compared to women with no previous pregnancies.

The researcher doing the Australian study also found the risk of prematurity following an abortion higher than the risk associated with other factors that have sometimes been connected with prematurity, such as maternal age, number of previous pregnancies, marital status, and socioeconomic status. She also noted that each preterm birth increased the likelihood of subsequent preterm births, while each full-term birth diminished the risk.

Notably, most of the abortions involved were vacuum aspirations rather than dilation and curettage, a strong indicator that the risk was more than simply a matter of more aggressive surgical intervention.

These 1993 results were confirmed in 1998 by the same researcher in a follow-up study that involved twice as many Australian births. Besides validating earlier results, the researcher found women with four or more abortions had nine times the risk of extremely premature births as women with no prior pregnancies.

A 1994 German study tracking 106,345 births in Bavaria showed similar results. A woman having one previous abortion had two and a half times the risk of having a subsequent premature birth. (In this study, this was considered as any birth at less than 32 weeks gestation.) The risk was 5.2 times higher for a woman with two previous abortions and eight times higher for a woman with three or more previous abortions.