• Maria P Velez, Marina Ivanova, Jonas Shellenberger, Jessica Pudwell, and Joel G Ray.
• Department of Obstetrics and Gynaecology, Queen's University Kingston, Ontario, Canada; and ICES, Ontario, Canada (M.P.V.).
• Ann. Intern. Med. 2024 Nov 1; 177 (11): 148214881482-1488.

BackgroundUse of a gestational ("surrogate") carrier is increasingly common. Risk for maternal and neonatal adversity is largely unknown in this birthing population.ObjectiveTo determine the risk for severe maternal morbidity (SMM) and severe neonatal morbidity (SNM) in gestational carriers.DesignPopulation-based cohort study.SettingAll of Ontario, Canada.ParticipantsAll singleton births at more than 20 weeks' gestation, from 2012 to 2021.MeasurementsExposure was type of conception, namely, gestational carriage (main exposure), unassisted conception (comparison group 1), and in vitro fertilization (IVF) (comparison group 2). Main composite outcomes were SMM and SNM. Modified Poisson regression models generated weighted relative risks (wRRs) using propensity score-based overlap weighting. Secondary outcomes included hypertensive disorders of pregnancy, cesarean delivery, preterm birth, and postpartum hemorrhage.ResultsOf all eligible singleton births, 846 124 (97.6%) were by unassisted conception, 16 087 (1.8%) by IVF, and 806 (0.1%) by gestational carriage. Respective risks for SMM were 2.3%, 4.3%, and 7.8%. The wRRs were 3.30 (95% CI, 2.59 to 4.20) comparing gestational carriage with unassisted conception and 1.86 (CI, 1.36 to 2.55) comparing gestational carriage with IVF. Respective risks for SNM were 5.9%, 8.9%, and 6.6%, generating wRRs of 1.20 (CI, 0.92 to 1.55) for gestational carriage versus unassisted conception and 0.81 (CI, 0.61 to 1.08) for gestational carriage versus IVF. Hypertensive disorders, postpartum hemorrhage, and preterm birth at less than 37 weeks were also significantly higher contrasting gestational carriers to either comparison group.LimitationAbsence of information about indications for choosing a gestational carrier, and oocyte or sperm donor source.ConclusionAmong singleton births of more than 20 weeks' gestation, a higher risk for SMM and adverse pregnancy outcomes was seen among gestational carriers compared with women who conceived with and without assistance. Although gestational carriage was associated with preterm birth, there was less clear evidence of severe neonatal morbidity. Potential mechanisms for higher maternal morbidity among gestational carriers require elucidation, alongside developing special care plans for gestational carriers.Primary Funding SourceThe Canadian Institutes of Health Research.

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