Cryopreserved embryo replacement might be linked to increase in birthweight

For the same couple, the birthweight of the second child born from a thawed embryo replacement is significantly higher than that of the first child born from a fresh embryo replacement. — encrier/IStock.com pic via AFP
For the same couple, the birthweight of the second child born from a thawed embryo replacement is significantly higher than that of the first child born from a fresh embryo replacement. — encrier/IStock.com pic via AFP

MONTREAL, Oct 13 — A study conducted by Montpellier University Hospital and Grenoble-Alpes University Hospital in France and the Clinique Ovo in Montreal, Canada indicates that newborns who were conceived from cryopreserved embryo replacement weighed an average of 250g more at birth than those conceived from fresh embryos.

The research, which was published in Scientific Reports, compared the birthweight of children conceived from a single frozen embryo to that of their elder siblings conceived from a single “fresh embryo.”

The objective of the study was to determine whether the freezing/thawing procedure had an incidence in the discrepancy in the context of medically assisted reproduction.

This represents the first observational study to compare neonatal data from singleton pregnancies (eg, a single child as opposed to twins) resulting in the transfer of single, fresh embryos for a first pregnancy, and “frozen” for the second, taken from the same oocyte retrieval.

Results show that for one couple, the birthweight of the second child born from a thawed embryo replacement is significantly higher (on average weighing 3.5 kg) than that of the first child born from a fresh embryo replacement (on average weighing 3.25 kg).

Adjusting the results for maternal factors such as age, body mass index, number of embryos transferred, and day of embryo transfer suggests a discrepancy of 271 g between the child born from a frozen embryo transfer and its elder sibling born from an unfrozen embryo.

According to Samir Hamamah, Professor in Reproductive Medicine and hospital Practitioner, Medical school and University-hospital Montpellier, France, who coordinated the study: “We could also hypothesise that in the FET (frozen embryo transfer) group, the intrauterine environment was more favorable to embryo growth because it was not affected by controlled ovarian stimulation treatments in comparison with fresh embryo transfer.”

The study has also demonstrated that the birthweight of frozen embryo-conceived children was also higher than the French average for natural pregnancies, eg, those that did not result from medical assistance.

More studies are required to confirm to link between the freezing of embryos and birthweight, as reported by Pr Hamamah. — AFP-Relaxnews

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