Birthweight distribution in ART singletons resulting from embryo culture in two different culture media compared with the national population

birthweight. main results and the role of chance: We found no significant difference in the crude birthweight distributions between singletons born after culture in Cook-d2 or Medicult-groups. Singleton girls from the Cook-d2 group weighed 3302+ 28 g, versus 3252+ 76 in the Medicult-d2 group (difference 50 g; P ¼ 0.547). Singleton boys from the Cook-d2 group weighed 3430+ 27 g, versus 3354+ 56 in the Medicultd2 group (difference 76 g; P ¼ 0.279). In the background population, mean birthweights for singleton girls and boys were 3383+ 2.4 g and 3494+ 2.5 g, respectively. The mean birthweights of girls, 3315+ 61 g, and boys, 3383+ 64 g, in the Medicult-d3 group were not significantly different from that in the Medicult-d2 group. When pooling data from all culture media groups, we found the same slightly lower mean birthweight in IVF/ICSI singletons when compared with the national birth cohort as has been previously reported (Cook-d2 + Medicult-d2 + d3 versus birth cohort; girls: P , 0.001, boys: P , 0.001). We also pooled data on boys and girls and calculated the mean birthweight for the Cook-d2, Medicult-d2 and Medicult-d3 groups and found no significant differences. limitations, reasons for caution: The retrospective design and the inherent risk of confounding factors is a limitation. Selection bias cannot be excluded as the embryos cultured in Cook-d2 and Medicult-d2 were from single centre studies while data in Medicult-D3 group were derived from a multicentre study.