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

Published:January 17, 2023DOI:


      Research question

      What are the risk factors for prematurity other than intrauterine growth restriction in singletons after in vitro fertilization?


      Data were collected from a national registry, based on an observational prospective cohort of 30737 livebirths after assisted reproductive technologies (ART) between 2014 and 2015. A population of not-small-for-gestational-age singletons conceived after fresh embryo transfers and frozen-thawed embryo transfers and their parents was selected. Main collected data: parent's age, type of infertility, number of oocytes retrieved, semen origin, type of fertilization, number of transferred embryos, embryo age at transfer, vanishing twins, gestational age at birth, birthweight and sex.


      Data from 20 932 fresh embryo transfers and 9805 frozen-thawed embryo transfers of singletons were collected. Preterm birth occurred in 7.7% (n=1607) of fresh embryo transfers and 6.6% (n=611) of frozen-thawed embryo transfers (p<0.0001; adjusted OR = 1.34 [1.21-1.49]). Endometriosis, and vanishing twin increased the risk of preterm birth after fresh embryo transfer (p<0.001; respectively aOR 1.32 and 1.78). Polycystic ovaries or >20 oocytes retrieved also increased preterm birth risk (aOR 1.3; respectively p =0.003 and p=0.02), while large oocyte cohort (>20) was no longer associated with the risk of prematurity in case of frozen embryo transfer.


      Endometriosis remains a risk of prematurity even in the absence of intrauterine growth retardation, which suggests a dysimmune impact. Large oocyte cohorts obtained by stimulation, without clinical PCOS diagnosed before attempts, have no further impact in case of frozen embryo transfer, reinforcing the idea of a phenotypic difference in the clinical presentation of PCOS.



      AMH (Anti-mullerian hormone), ART (Assisted Reproductive Technology), FET (Frozen embryos transfer), FGR (Fetal growth restriction), fresh-ET (Fresh embryos transfer), IVF (In vitro fertilization), Not-SGA (not-small-for-gestational-age), PCOS (Polycystic Ovary Syndrome)
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      Marie-Jose Gervoise Boyer is a doctor specialising in reprotoxicity. She has been working since 1984 on the risks associated with pre-conception or in utero drug exposure and has extensive experience in paediatric pharmacovigilance. Since 2000, she has been interested in the follow-up of children born after medically assisted procreation.