Researchers led by Dr Peter Sjöblom from Nottingham University's NURTURE IVF clinic found the average birth weight of 165 IVM babies was six to nine per cent higher than babies conceived by IVF/ICSI. The IVM babies' birth weights were also 0.3 to six per cent higher than the national average for singleton births.
Caesarean rates were also consistently higher after IVM: 30 - 60 per cent for singleton IVM births versus 27 - 44 per cent for IVF/ICSI. IVM pregnancies had high miscarriage rates (25 to 37 per cent) and the average gestation period was three to 11 days longer than IVF/ICSI.
The researchers also speculated that IVM births might require more inductions, vacuum extractions and forceps deliveries than IVF/ICSI and natural births.
'We looked at four different data sets from four different countries and, although the numbers were small and differences modest, we saw a consistent pattern that cannot be ignored. We strongly believe that these findings must be explored further', Dr Sjöblom said.
The team looked at data from four studies of babies born after IVM, IVF and ICSI in Denmark, Finland, Canada and Korea. Statistical analysis was only possible for one of the studies because distribution data for the babies born after IVM or national averages were missing.
Dr Sjöblom and his team believe that, because IVM involves collecting and maturing immature eggs outside the body, it could interfere with early development. But the exact mechanisms leading to the observed results remain unclear and studies of more babies born by IVM will be needed before the risks are fully understood.
'[…W]ith much larger numbers, we can obtain accurate information on the health of these children. This will enable us to have reliable data with which to inform prospective parents about any possible risks associated with the procedure', said André van Steirteghem, Professor Emeritus of the Vrije Universiteit Brussel (VUB) medical school, who was not involved in the study.
Although IVM is rarely used in the UK at the moment, it offers the possibility to make ovarian stimulation obsolete, thereby reducing the costs of fertility treatment. Furthermore, it is valuable for women with cancer who need egg collection urgently.
The team presented their results at the 26th annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Rome, 27th to 30th of June.