In a national population-based controlled, follow-up study, Danish researchers have reported better neonatal outcomes in singletons born after the transfer of cryopreserved embryos as opposed to fresh cycle embryos. The study results were published in the online issue of the journal, Fertility and Sterility.

Anja Pinborg from the Fertility Clinic, Copenhagen University Hospital, Denmark, and colleagues, conducted the study using data of 957 cryo singletons (Cryo-IVF=660; Cryo-ICSI=244; Cryo-IVF/-ICSI=53) between 1995 to 2007 to evaluate the postnatal outcome following the transfer of cryopreserved embryos. Two control groups were selected during the same study period: the first comprised of all singleton births after fresh IVF (n=6904) or ICSI (n=3425), and the second involved the random selection of non-ART singletons (n=4800). Preterm birth (PTB; <37 weeks), congenital malformations, low birth weight (LBW; <2500 g), mortality, and morbidity were the main outcomes measured.

The study results showed that the mean birth weight of the cryo, fresh, and non-ART singletons were 3,578 g, 3,373 g, and 3,537 g, respectively. The adjusted risk of LBW (OR=0.63) and PTB (OR=0.70) was found to be lower in the cryo group compared to the fresh subset. Similar findings were observed on comparing cryo and non-ART groups; however, the perinatal mortality rate (1.6% vs. 0.8%) and adjusted risks of very low PTB (<34 weeks) and neonatal hospital admission was higher in cryo singletons. Also, no substantial variation was noticed between the cryo and the 2 control groups with respect to the prevalence rates of neurological sequelae, birth defects, imprinting-related diseases, and malignancies. The comparison between the total fresh and non-ART groups, however, demonstrated comparatively higher rates of malformation and cerebral palsy in the offspring born after the transfer of fresh embryos.

A report presented at the 2008 ESHRE meeting by the International Committee Monitoring Assisted Reproductive Technologies (ICMART) estimates that around 25% of ART-conceived children (globally) are born after the transfer of cryopreserved embryos. There is an increasing trend towards the transfer of fewer embryos owing to the complications associated with multiple gestations, which has in turn led to the availability of more embryos for freezing. However, there is lack of sufficient data on the safety of the cryopreservation technique with respect to the neonatal outcome and child follow-up.

Although several studies have indicated improved neonatal outcomes in children born after frozen embryo transfer compared to fresh cycles, the reason for this is not clearly known. This emphasizes the need for further research to elucidate the relationship and also further assess the long-term health outcomes in the offspring born after ART.

References

1. Pinborg A, Loft A, Aaris Henningsen AK, Rasmussen S, Nyboe Andersen A. Infant outcome of 957 singletons born after frozen embryo replacement: The Danish National Cohort Study 1995-2006. Fertil Steril. 2009 Jul 30. [Epub ahead of print].

2. Wennerholm UB, Söderström-Anttila V, Bergh C, et al. Children born after cryopreservation of embryos or oocytes: a systematic review of outcome data. Hum Reprod. 2009 Sep;24(9):2158-72.