Fertility-assisted pregnancies more likely to deliver preterm

In the United States, singleton neonates conceived by fertility treatment are significantly more likely to be born preterm than those conceived naturally, according to a cohort study in JAMA Network Open.¹

“Preterm birth is a global health issue,” wrote the authors. “The association between fertility treatment and preterm singleton births has not been clarified.”

The study used birth data from all 50 states—and the District of Columbia—in the National Vital Statistics System database. All mothers in the database who had a singleton live birth between January 2016 and December 2019 were included, representing 14,370,920 mothers with a mean age of 28.79 years for the final sample.

Fertility treatment was categorized as either assisted reproductive technology (ART) or non-ART treatment.

The primary outcome was a diagnosis of preterm birth, which was defined as birth before 37 complete weeks of gestation. Gestational age was calculated by obstetric estimation at delivery and collected from the database.

The prevalence of preterm birth among the sample was 7.6% for natural conception, 10.7% for ART, and 9.3% for non-ART.

Compared to neonates who were naturally conceived, newborns conceived with ART were 49% more likely to be preterm, after full adjustment (P < 0.001).

Similarly, non-ART treatment was linked to a 35% increased risk of preterm birth versus natural conception, after full adjustment (P < 0.001).

Preterm birth was divided into 3 delivery periods—extremely preterm delivery (<28 weeks), very preterm delivery (from 28 to 31 weeks and 6 days), and moderately and late preterm delivery (between 32 and 36 weeks and 6 days).

Of the 7.6% preterm births, 6.6% were deemed moderately and late preterm delivery, 0.6% very preterm delivery, and 0.4% extremely preterm delivery.

The incidence of very preterm and extremely preterm births were significantly higher in the ART and non-ART treatment groups compared to the natural conception group—1.0% vs 0.8% vs 0.4% (P < 0.001).

Neonates who were conceived after ART or non-ART treatment also had a higher prevalence of low birth weight (< 2500 g) than those who were naturally conceived—7.7% vs 7.3% vs 6.1% (P < 0.001).

Compared to the natural conception group, the risk of very preterm birth was 68% higher in the ART group (P < 0.001) and 46% higher in the non-ART treatment group (P < 0.001) after full adjustment.

The risk of extremely preterm birth increased by 88% in the ART group (P < 0.001) and by 83% in the non-ART treatment group (P < 0.001) compared to the natural conception group after full adjustment.

The authors noted that their results mirror existing studies that found an increased risk of preterm birth lined to fertility treatment–assisted pregnancies.

“However, in the stratified analyses, we observed no fertility treatment–associated increase in the risk of preterm birth among women with a history of preterm delivery,” they wrote.

Reasons for this finding could be that women undergoing fertility treatment with a history of preterm delivery pay more attention to perinatal care, or that they are less likely to be infertile.

Reference

1. Wang R, Shi Q, Jia B, et al. Association of preterm singleton birth with fertility treatment in the U.S. JAMA Netw Open. Published online February 8, 2022. doi:10.1001/jamanetworkopen.2021.47782