Pregnancy Soon After Abortion Ups Risk of Preterm Birth

Women who waited less than 6 months to become pregnant following an abortion showed a small, but significant, increased risk of preterm birth in their subsequent pregnancy, researchers found.

Compared with women who waited 18 to 24 months to conceive again, those with an interpregnancy interval of less than 6 months following a pregnancy termination had a 35% increased risk of preterm birth (adjusted OR 1.35, 95% CI 1.02-1.77, P=0.034), reported Janna Männisto, MD, of University Hospital of Oulu in Finland, and colleagues.

However, there were no significant differences in the risk of low birth weight (less than 2,500 g) or small-for-gestational-age infants, the team wrote in Obstetrics & Gynecology.

The World Health Organization currently recommends interpregnancy intervals of "at least 6 months" following a miscarriage or termination of pregnancy, but Männisto and colleagues noted that this was based on the results of a single study that "did not make the distinction between miscarriages and terminated pregnancies, which therefore meant that there was heterogeneity in the study group."

The new study examined data from 19,894 women in the Finnish Register of Induced Abortions, who both underwent a termination of pregnancy and went on to have a subsequent live birth. Overall, the median interpregnancy interval was 21 months -- although 45% of the sample waited 24 months or longer to conceive again, followed by 16.1% who waited 6 to 12 months, and 14.9% who waited less than 6 months.

In a podcast released to the media, Nancy Chescheir, MD, editor-in-chief of Obstetrics & Gynecology, characterized the paper as "particularly useful," because patients frequently raise the question about whether pregnancy termination increases risks in the next pregnancy.

She added that because the risk of preterm birth appears to be similar for short intervals between live births, this may suggest that it's not "what happened to the pregnancy," but rather, the short interval itself that may determine whether there are complications.

"Whether it's the hormonal milieu, something inflammatory inside the uterus that needs to heal, or whether it's maternal deprivation syndrome or stress -- all those different things we don't know much about, yet they may be issues between one of them and the beginning of the next pregnancy," Chescheir explained. "But it's awfully reassuring that after 6 months, there does not seem to be any impact."

Overall, the rates of adverse neonatal outcomes within the entire population were less than 5%:

• Preterm birth: 4.5%
• Low birth weight: 3.6%
• Small-for-gestational-age: 2.5%

But the incidence of preterm birth among women who waited less than 6 months to conceive again was significantly higher than for women with a longer interpregnancy interval (5.6%, P value for X² test= 0.008). The mean gestational age at birth was statistically significant, but likely not clinically significant -- as all neonates had a mean gestational age of 39.3 to 39.5 weeks at birth.

Factors that contributed to a shorter interpregnancy interval as shown in the study included maternal age (i.e., younger women), women with second-trimester pregnancy terminations, and women with previous deliveries. Fetal anomalies or abnormalities also made up 20.7% of the pregnancy terminations for women with an interpregnancy interval of less than 6 months.

The authors noted that these women were "overrepresented" in the short interpregnancy interval group, because "when the indication for termination is fetal anomaly or abnormality, a new pregnancy as soon as possible is often wanted." However, even after excluding these women, the association between preterm birth and an interpregnancy interval of less than 6 months persisted.

One limitation to the study may be potential unmeasured confounders that cannot be ruled out in contributing to the risk of subsequent preterm birth, the researchers wrote.

Chescheir said that this emphasizes the importance of ensuring that patients who have undergone an abortion have adequate access to contraception: "Women who have had a termination will ideally leave the procedure area with an active contraceptive plan or one that can be put into place."

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