In pregnancies conceived with infertility treatment, delivery at 39 weeks’ gestation results in the lowest perinatal risk compared with delivery at subsequent week of gestation, according to a study published in JAMA Network Open.
Researchers conducted a retrospective cohort study to identify the optimal gestational age for minimizing stillbirth risk in term singleton pregnancies conceived with infertility treatment or assisted reproductive technology (ART). The team included 178,448 term pregnancies (mean maternal age, 34.2 years; mean gestational age, 39.2 weeks) abstracted from linked birth/infant death and fetal death records between 2014 and 2018. Only singleton pregnancies conceived through infertility treatment and delivered within 37 to 42 weeks of gestation were included in the investigation.
The stillbirth rate was 0.14%, and infant death rate was 0.07%, according to the report. Compared with spontaneous pregnancies, individuals undergoing infertility treatments were more likely to be non-Hispanic White, aged 35 years and older, and have nulliparity. Spontaneous pregnancies had a lower preterm delivery rate at less than 37 and 34 weeks’ gestation (9.1% and 2.6%, respectively) compared with pregnancies using infertility treatments (11.0% and 3.5%, respectively).
In pregnancies conceived with infertility treatment, the stillbirth rate per 10,000 ongoing pregnancies increased with each week of term gestation between 37 and 42 weeks, the report shows. The lowest value was noted at 37 weeks (3.1; 95% CI, 2.3-4.0 per 10,000 ongoing pregnancies) and the highest was observed at 42 weeks (21.0; 95% CI, 11.0-39.7 per 10,000 ongoing pregnancies). ART pregnancies showed a similar trend, with 2.5 stillbirths (95% CI, 1.7-3.7) per 10,000 ongoing pregnancies at 37 weeks and 23.6 stillbirths (95% CI, 10.8-51.4) per 10,000 ongoing pregnancies at 42 weeks.
Infant mortality rates per 10,000 live births were lowest at 39 weeks for both pregnancies conceived with infertility treatments (6.2; 95% CI, 4.2-9.1) and with ART (5.2; 95% CI, 3.2-8.1). In pregnancies conceived with infertility treatment, delivery risk was lowest at 37 and 38 weeks’ gestation, with higher mortality risks at 38 weeks and later. At 39 weeks’ gestation and later, the risk ratio (RR) of delivery in the subsequent vs given week of gestation exceeded the risk of delivery (RR, 1.25; 95% CI, 1.19-1.31), according to the report.
Study limitations include its retrospective design and a lack of data regarding intent or indication for delivery.
“In this cohort study, delivery at 39 weeks was associated with the lowest perinatal risk when comparing the risk of delivery at a given week vs subsequent week of gestation,” according to the study authors. “The findings suggest an increased risk of adverse perinatal outcomes with both early-term and late-term delivery among patients who conceived with infertility treatment.”
Hamilton I, Martin N, Liu J, DeFranco E, Rossi R. Gestational age and birth outcomes in term singleton pregnancies conceived with infertility treatment. JAMA Netw Open. Published online August 1, 2023. doi:10.1001/jamanetworkopen.2023.28335