Gestational Age and Birth Outcomes in Term Singleton Pregnancies Conceived With Infertility Treatment

IMPORTANCE: Despite the increased perinatal risks associated with pregnancies conceived with infertility treatment, there are no recommendations for timing of delivery among this at-risk population. OBJECTIVE: To identify the gestational age at which the ongoing risks of stillbirth are optimally balanced with the risks of neonatal comorbidities and infant deaths in term singleton pregnancies conceived with infertility treatment. DESIGN, SETTING, AND PARTICIPANTS: This cohort study used birth and death data from January 1, 2014, to December 31, 2018, in the US obtained from the National Center for Health Statistics. Singleton pregnancies conceived with infertility treatment delivered at term (37-42 weeks’ gestation) were eligible for inclusion. The exclusion criteria were deliveries at less than 37 weeks’ or at least 43 weeks’ gestation and pregnancies with unknown history of infertility treatment, congenital anomalies, pregestational diabetes, pregestational hypertension, gestational hypertension, and preeclampsia. Data were analyzed from July 22, 2022, to June 24, 2023. EXPOSURE: Gestational age at delivery between 37 and 42 weeks. MAIN OUTCOMES AND MEASURES: The primary outcome was optimal timing of delivery. To ascertain this timing, the risk of delivery (rate of neonatal morbidity and infant death) at a given gestational week was compared with the risk of delivery in the subsequent week of gestation for an additional week (rate of stillbirth during the given week per 10 000 ongoing pregnancies plus rate of neonatal morbidity and infant death in the subsequent week of gestation per 10 000 deliveries). The rates of stillbirth, neonatal morbidity, and infant death (within 1 year of life) were compared at each week. Neonatal morbidity included an Apgar score of 3 or lower at 5 minutes, requirement of ventilation for 6 hours or more, neonatal intensive care unit admission, and seizures. RESULTS: Of the 178 448 singleton term pregnancies conceived with infertility treatment (maternal mean [SD] age, 34.2 [5.2] years; mean [SD] gestational age, 39.2 [1.2] weeks; 130 786 [73.5%] were non-Hispanic White patients). The risk of delivery in the subsequent week of gestation was lower than the risk of delivery at both 37 weeks (628 [95% CI, 601-656] vs 1005 [95% CI, 961-1050] per 10 000 live births) and 38 weeks (483 [95% CI, 467-500 vs 625 [95% CI, 598-652] per 10 000 live births). The risks of delivery in subsequent week of gestation significantly exceeded the risk of delivery at 39 weeks (599 [95% CI, 576-622] vs 479 [95% CI, 463-495] per 10 000 live births) and were not significant at 40 weeks (639 [95% CI, 605-675] vs 594 [95% CI, 572-617] per 10 000 live births) and 41 weeks (701 [95% CI, 628-781] vs 633 [95% CI, 599-669] per 10 000 live births). CONCLUSIONS AND RELEVANCE: Results of this study suggest that, in pregnancies conceived with infertility treatment, delivery at 39 weeks provided the lowest perinatal risk when comparing risk of delivery at this week of gestation vs the subsequent week of gestation.