IVF babies grown from frozen embryos are more likely to be oversized, say researchers.
A study has shown frozen embryos produce bigger babies
IVF babies born from frozen embryos are more likely to be oversized, compared to those born from "fresh" embryos or conceived naturally, research has shown.
Researchers from the University of Copenhagen who led the study believe the freezing and thawing process may cause genetic changes that encourage bigger babies.
The Danish study compared 910 babies born from embryos that had been frozen, stored and thawed with 9,603 babies born after fresh embryo transfer and 4,656 naturally conceived little ones.
The proportion of large-for-gestational-age babies was 16.9% for the frozen embryo group, compared with 10.3% for the fresh transfer group and 11.4% for naturally conceived babies.
The average newborn weighs 7lbs 8oz, while babies who tip the scales at 9lbs 15oz or more are considered much larger than average, or macrosomic.
High birth weight babies are more likely to be delivered by Caesarean section or need other kinds of intervention that may lead to complications, while a vaginal delivery can mean an increased risk of tearing for mum.
The same study also found the use of frozen embryos greatly reduced the risk of having a baby that is too small. Just 9.2% of frozen embryo babies were small-for-gestational age compared with 14.8% of 'fresh' IVF babies and 11.3% of naturally conceived newborns.