Fetal growth disorders following medically assisted reproduction: due to maternal context or techniques? A national French cohort study

•Risk of small for gestational age was higher following fresh embryo transfer.•Risk of small for gestational age was higher following intrauterine insemination.•Risk of large for gestational age was higher following frozen embryo transfer.•These risks were also observed in the absence of obstetrical or neonatal morbidity.•Medically assisted reproduction is a risk factor for fetal growth disorders. What part do maternal context and medically assisted reproduction (MAR) techniques play in the risk of fetal growth disorders? This retrospective nationwide cohort study uses data available in the French National Health System database and focuses on the period from 2013 to 2017. Fetal growth disorders were divided into four groups according to the origin of pregnancy: fresh embryo transfer (n = 45,201), frozen embryo transfer (FET, n = 18,845), intrauterine insemination (IUI, n = 20,179) and natural conceptions (n = 3,412,868). Fetal growth disorders were defined from the percentiles of the weight distribution according to gestational age and sex: small and large for gestational age (SGA and LGA) if 90th percentiles, respectively. Analyses were performed using univariate and multivariate logistic models. Compared with births following natural conception, multivariate analysis showed that the risk of SGA was higher for births following fresh embryo transfer and IUI (adjusted odds ratio [aOR] 1.26 [1.22–1.29] and 1.08 [1.03–1.12], respectively) and significantly lower following FET (aOR 0.79 [0.75–0.83]). The risk of LGA was higher for births following FET (aOR 1.32 [1.27–1.38]), especially in artificial cycles when compared with ovulatory cycles (aOR 1.25 [1.15–1.36]). In the subgroup of births without any obstetrical or neonatal morbidity, the same increased risk of SGA and LGA were observed following fresh embryo transfer or IUI and FET (aOR 1.23 [1.19–1.27] or 1.06 [1.01–1.11] and aOR 1.36 [1.30–1.43], respectively). An effect of MAR techniques on the risks for SGA and LGA is suggested independently from maternal context and obstetrical or neonatal morbidities. Pathophysiological mechanisms remain poorly understood and should be further evaluated, as well as the influence of embryonic stage and freezing techniques.