Placental disorders of pregnancy in subsequent IVF pregnancies – a sibling cohort

To assess whether the incidence of placental disorders of pregnancy decreases with increasing parity in repeat IVF pregnancies, in the same way as natural pregnancies. This was a retrospective cohort of deliveries between November 2008 and January 2020, in a single university-affiliated medical centre. The study included women with only IVF-attained singleton pregnancies (no natural conception) with at least two deliveries, and compared the obstetric and perinatal outcomes between first, second and third deliveries. Each woman served as her own control. The primary outcome was the incidence of placental-related disorders of pregnancy, defined as small for gestational age (SGA) neonates and/or pre-eclampsia. A total of 307 first deliveries, 307 second deliveries and 49 third deliveries by the same women were compared. A trend for a decreased rate of pre-eclampsia was noted with increased parity (P = 0.06) and a significant decrease in the rate of SGA: 11.7% for first delivery, 7.8% for second delivery and 2.0% for third (P = 0.04). This difference in SGA incidence was maintained in a matched sub-analysis of the 49 women with three deliveries (P = 0.04), and after adjustment for fresh/frozen embryo transfer (P = 0.03). Although SGA and pre-eclampsia were generally more common in IVF than natural pregnancies, their decrease with increasing parity mimicked that in natural pregnancies. IVF pregnancies are associated with an increased risk of placental disorders of pregnancy. However, they exhibit a decrease in incidence with increasing parity.