Risk factors associated with preterm birth in singletons born after IVF: a national cohort study

Area of Science:

• Reproductive Medicine
• Obstetrics
• Infertility Research

Background:

• Assisted reproductive technology (ART) is associated with increased risks of preterm birth.
• Identifying specific risk factors beyond intrauterine growth restriction is crucial for improving ART outcomes.

Purpose of the Study:

• To investigate risk factors for preterm birth in singleton pregnancies conceived via in vitro fertilization (IVF), excluding intrauterine growth restriction.
• To differentiate risk factors associated with fresh embryo transfers versus frozen embryo transfers (FET).

Main Methods:

• Observational prospective cohort study of 30,737 live births after ART (fresh and FET) between 2014-2015.
• Analysis of singleton births classified as not-small for gestational age, examining variables like infertility type, oocyte retrieval numbers, and vanishing twins.

Main Results:

• Preterm birth rates were 7.7% for fresh embryo transfers and 6.2% for FET.
• Endometriosis and vanishing twin significantly increased preterm birth risk after fresh embryo transfer.
• Polycystic ovaries and retrieving over 20 oocytes were associated with higher preterm birth risk in fresh transfers, but not FET.

Conclusions:

• Endometriosis poses a risk for prematurity independent of intrauterine growth retardation, suggesting a potential dysimmune mechanism.
• Large oocyte cohorts from ovarian stimulation do not appear to increase preterm birth risk with FET, indicating potential phenotypic differences in polycystic ovary syndrome.