Incidence of pre‐eclampsia in triplet pregnancies with and without embryo reduction

ABSTRACT Objective To determine the risk of pre‐eclampsia (PE) in triplet pregnancies, with and without embryo reduction, compared to singleton and twin pregnancies. Methods This was a retrospective multicenter study of triplet pregnancies with three live, phenotypically normal fetuses at the 11–13‐week scan and a gestational age at delivery of ≥ 24 weeks. The competing‐risks model was used to determine the distribution of gestational age at delivery with PE in each type of triplet pregnancy, which was compared to datasets from 1169 twin pregnancies and 61 174 singleton pregnancies from previous cohorts. The relative risks of PE with delivery < 37, < 34 and < 32 weeks' gestation for non‐reduced and reduced triplet pregnancies, in comparison with twin and singleton pregnancies, were determined. Results Overall, 1020 triplet pregnancies were included, of which 456 had expectant management, 468 were reduced to twin pregnancies and 96 were reduced to singleton pregnancies. The incidence of PE with delivery < 37 weeks' gestation was 9.9% for non‐reduced triplet pregnancies, 9.8% for triplet pregnancies reduced to twins, 2.1% for triplet pregnancies reduced to singleton, 7.0% for twin pregnancies and 0.8% for singleton pregnancies. The incidence of PE with delivery < 34 weeks was 7.2% for non‐reduced triplets, 4.1% for triplets reduced to twins, 0% for triplets reduced to singleton, 0.9% for twins and 0.4% for singletons. In comparison with singleton pregnancies, for non‐reduced triplets, the relative risks for PE with delivery < 37 and < 34 weeks were 12.3 (95% CI, 9.1–16.3) and 20.6 (95% CI, 14.4–29.2), respectively. The respective values for triplet pregnancies reduced to twins were 12.2 (95% CI, 9.1–16.2) and 11.6 (95% CI, 7.3–18.2), and for triplet pregnancies reduced to singleton they were 2.6 (95% CI, 0.7–9.1) and 0.0 (95% CI, 0.0–11.0). In comparison with twin pregnancies, for non‐reduced triplets the relative risks for PE with delivery < 37 and < 34 weeks were 1.4 (95% CI, 1.0–2.0) and 7.7 (95% CI, 4.0–14.9), respectively. The respective values for triplets reduced to twins were 1.4 (95% CI, 1.0–2.0) and 4.3 (95% CI, 2.1–8.9). For a given set of maternal characteristics and medical history, a non‐reduced triplet pregnancy was estimated to deliver with PE, on average, 14.5 weeks earlier than would a singleton pregnancy. Triplet pregnancies reduced to twins were estimated to deliver with PE 12.7 weeks earlier, and those reduced to singleton 6.5 weeks earlier, than would comparable singleton pregnancies. Conclusion Non‐reduced triplet pregnancies have a 21‐fold and 8‐fold higher risk of delivery with PE at < 34 weeks' gestation compared with singleton and twin pregnancies, respectively. In triplet pregnancies reduced to twins, the relative risk of PE < 34 weeks is 4‐fold higher than that in twin pregnancies, whereas in triplet pregnancies reduced to singleton, the risk is similar to that of singleton pregnancies. © 2026 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.