Analysis of risk factors for very early preterm and early preterm birth in twins following in vitro fertilization and intracytoplasmic sperm injection–assisted pregnancy: A retrospective study

To investigate the risk factors influencing very early preterm and early preterm births in twin pregnancies after in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). This retrospective study analyzed 2042 twin pregnancies that underwent embryo transfer via IVF/ICSI at the Reproductive Center of Sir Run Run Shaw Hospital between January 2019 and December 2022. Spontaneous very early, early preterm, and provider-initiated preterm births were examined separately. Based on gestational age, participants were categorized into three groups: very early preterm birth (<28 weeks), early preterm birth (≥28 to <34 weeks), and ongoing pregnancy (≥34 weeks). Univariate analysis was conducted to assess general conditions, among the three groups. Multiple logistic regression analysis was performed to identify independent risk factors for very early and early spontaneous preterm birth in twin pregnancies. A total of 2042 twin pregnancies were included in the study, with birth rates of 4.36% (89 of 2042) <28 weeks, 12.14% (248 of 2042) ≥28 to <34 weeks, and 83.50% (1705 of 2042) ≥34 weeks. The primary cause of provider-initiated preterm birth <28 weeks was placental factors, while hypertensive disorders of pregnancy (31.11%) were the predominant cause for preterm births ≥28 to <34 weeks. Multiple logistic regression analysis identified the independent risk factors for births <28 weeks (P < 0.05) as cervical cerclage, history of late miscarriage or premature birth, uterine adhesions, primary infertility of polycystic ovary syndrome (PCOS), monochorionic pregnancies, history of cervical surgery, uterine malformations, body mass index ≥25 kg/m², and uterine longitudinal axis lengths <3.6 cm. Cervical cerclage, main factors of infertility (PCOS), adenomyosis, and uterine longitudinal axis lengths <3.6 cm were identified as independent risk factors for ≥28 to 34 weeks (P < 0.05). It is crucial to consider risk factors during IVF/ICSI treatment because of the high incidence of very early and early preterm twin pregnancies, which can be identified early and properly managed.