In vitro maturation (IVM) fertility treatment could mean difficult births, possibly caesarean, and larger than normal babies. Hence British researchers are urging caution until further studies can clarify their findings.
In the IVM process, immature eggs are retrieved from a woman's ovaries and matured in the lab before being fertilised and any resulting embryos transferred to the woman's uterus.
Authors of the literature review presented to the 26th annual meeting of the European Society of Human Reproduction and Embryology in Rome Wednesday.
"These findings suggest a significant impact of the IVM procedure on early development," said Dr Sj÷blom. "The pattern of increased birth weight, more obstetric interventions and possibly a longer gestation period are consistent with Large Offspring Syndrome. It cannot be explained by there being a higher proportion of women with polycystic ovarian syndrome in the IVM group, since the birth weight of their offspring was not significantly different from babies born after natural conception.
"We urge IVM practitioners and clinics to pool their data on obstetric and neonatal outcomes after fertility treatments because, at present, only limited data on small numbers of births are available. This should enable us to look more closely at the health and physiology of babies born after fertility treatment so that we can make a more detailed assessment of infant health. If the observed pattern still holds as the number of observations increases, then in-depth studies of mechanisms must be initiated. Caution is called for before proceeding with IVM on a large scale."
Dr Peter Sj÷blom said: "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."
He said the possible mechanisms involved were unclear. "It has been described in the literature that gene expression is altered in IVM eggs compared to those matured naturally in the body; it may be the case that the final stages of egg development before ovulation involves events that are crucial to development and that this is not happening when they are matured in the lab. Another explanation could be that the preparation of the lining of the womb (the endometrium) is different and this may influence development, as has been shown in animal studies."
The long-term consequences to the health of babies born after IVM are also unknown. "For the sake of the health and safety of the babies and their mothers, we need to be following IVM babies from the moment the eggs are matured in the laboratory through to their birth and into adulthood. We also need to look in detail into possible physiological effects, like alterations in blood pressure. However, we must make it clear to the public that, at the moment, no major health problems have been observed in children born after IVM. Nevertheless, all fertility clinics should share their detailed data, so that we can, hopefully, conclude that there is no reason for concern," concluded Dr Sj÷blom.