Abstract
Birth weight (BW) is higher after frozen embryo transfer (FET) than after fresh embryo replacement. No study has compared the BW of siblings conceived using the same oocyte/embryo cohort. The aim of this study was to determine whether the freezing-thawing procedure is involved in such difference. Multicenter study at Montpellier University Hospital, Clinique Ovo, Canada and Grenoble-Alpes University Hospital. The first cohort (Fresh/FET) included in vitro fertilization (IVF) cycles where the older was born after fresh embryo transfer (n = 158) and the younger after transfer of frozen supernumerary embryos (n = 158). The second cohort (FET/FET) included IVF cycles where older and younger were born after FET of embryos from the same cohort. The mean adjusted BW of the FET group was higher than that of the fresh group (3508.9 ± 452.4 g vs 3237.7 ± 463.3 g; p < 0.01). In the FET/FET cohort, the mean adjusted BW was higher for the younger by 93.1 g but this difference is not significant (3430.2 ± 347.6 g vs 3337.1 ± 391.9 g; p = 0.3789). Our results strongly suggest that cryopreservation is directly involved in the BW variation. Comparing BW difference between Fresh/FET cohort and FET/FET one, it suggests that parity is not the only responsible, increasing the role of cryopreservation step in BW variation.
Highlights
The first live births after in vitro fertilization (IVF) and frozen embryo transfer (FET) were reported in 1978 and 1984 respectively[1,2]
Maternal age was higher for singletons born after FET than after fresh embryo transfer and the birth order was always higher for children in the FET group (Table 3)
The mean Birth weight (BW) was higher after FET compared with fresh embryo transfer (3499.5 ± 468.3 g vs 3247.1 ± 506.1 g; p < 0.0001), no difference was detected for the FET/FET cohort (Table 3)
Summary
The first live births after in vitro fertilization (IVF) and frozen embryo transfer (FET) were reported in 1978 and 1984 respectively[1,2]. In a retrospective cohort study on sibling pairs, Pinborg et al showed that the sibling born after FET has an increased risk of being larger for gestational age than the sibling born after fresh embryo transfer. This demonstrated that intrinsic maternal factors are not the only reasons of the BW difference[8]. The aim of this study was to determine in a sibling embryo cohort whether the freezing-thawing procedure is involved in the BW difference between singletons born after fresh embryo transfer and after FET. From previous studies, here only siblings conceived from the same cohort of embryos (same IVF cycle) were included
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