Controversies in OB/GYN: Does elective abortion increase the risk of preterm delivery?

Yes. The risk increases with subsequent abortions.

Therapeutic abortion often is chosen (54%) in response to an unintended pregnancy.¹ In January 1973, protecting a woman's right to privacy as founded in the Fourteenth Amendment, the United States Supreme Court made abortion legal. In 2002, a total of 854,122 legal induced abortions were reported to the Centers for Disease Control and Prevention. Nearly 90% of these abortions were performed before 13 weeks' gestation. Of these induced abortions, 91% were completed surgically by dilation and evacuation (D&E).²

Preterm delivery after induced abortion is one outcome documented by research study. Approximately 24 articles in the literature address induced abortion and preterm delivery (PTD). These articles are divided over the topic, with half of the research demonstrating a risk of PTD after surgical abortion and the other half refuting the association. The power of the studies supporting a relationship of induced abortion with subsequent PTD is significantly higher than those in opposition, with 251,748 versus 43,245 subjects analyzed, respectively.³ The studies that did not demonstrate a significant risk of PTD in women who previously underwent surgical abortion, statistically speaking, were arguably underpowered to demonstrate that effect.

The mechanism by which induced abortion contributes to an increased risk of future PTD is not well delineated. Infectious etiologies have been implicated by many authors. Others point to damage to the endometrium from dilation and currettage procedures, which lead to improper placentation in ensuing pregnancies. Most recently, the EPIPAGE study reports that antepartum hemorrhage, placenta previa, and preterm premature rupture of membranes are associated causes in PTD after a prior induced abortion.⁴ Regardless of the physiologic and physical means, a current review of the literature supports a history of induced abortion as a risk factor for PTD, with odds ratios ranging from 1.1 to 2.9.^3,4 This risk also appears to increase with the number of previous abortions.⁴ With the significant prevalence of induced abortions in the US today, if we accept the causal relationship between prior abortion and PTD, even a modest increase in the odds ratio yields a dramatic impact on the number of PTDs.

The principle "first do no harm" helps to direct our mindset when counseling women who are deciding whether to proceed with termination or continue a pregnancy. In the face of current evidence, arguably women undergoing abortion should be informed of the potential harm the procedure holds in the form of PTD for future pregnancies. With the knowledge that nearly half of all abortions in the US are repeat abortions, it would be particularly important to tell women of the increasing risk of PTD with increasing number of previous abortions.⁵ Understanding the potential long-term health consequences of an induced abortion will enable women to more effectively provide informed consent for this procedure.

Preterm birth affects roughly 10% of deliveries today and remains the leading cause of infant morbidity and mortality. Even with considerable study, researchers and clinicians fail to alter the rate of PTD. Recent investigations and review of case–control and cohort studies from the past link induced abortion as a significant risk factor for PTD. Without an understanding of the cause of this relationship, we are unable to alter the current surgical and medical techniques employed for induced abortion. Therefore, until then, it seems imperative to educate women about the known risks of induced abortion. By reducing the number of abortions performed and discouraging repeat induced abortions, we may be able to significantly impact the rate of spontaneous PTD. We believe women contemplating abortion would benefit from this knowledge and that providers of abortion procedures have an autonomy-based obligation to make women aware of the potential future reproductive harm.