Scientists have found that the health of infants born through IVF depends on which techniques were used and their infertility diagnoses. The results indicate that the uterine environment is perhaps the most important influence on key obstetric outcomes: birth weight and the length of gestation.
Previous work in the field has shown that infants conceived through IVF are more likely to have a lower birth weight and shorter period of gestation compared to infants conceived naturally. This is significant as low birth weight and shorter gestational age are associated with increased infant morbidity and mortality.
Further studies looked at infants born to couples experiencing fertility problems comparing those who were conceived through IVF with those conceived naturally. The results showed no difference in birth weight or gestational age, suggesting that IVF treatment itself was not causing these adverse outcomes. The study concluded that factors relating to the underlying infertility were adversely affecting the health of the infant.
To shed more light on the effect of infertility on the health of the infant, Professor William Gibbons and his colleagues Professors Marcelle Cedars and Roberta Ness reviewed data collected by the Society for Assisted Reproductive Technologies for 2004 to 2006.
They looked at the effects of egg and sperm quality and the uterine environment. No adverse effect on birth weight or gestational age was observed when a couple's own egg or sperm was used in IVF compared to using a donor gamete. However, infants born to a surrogate mother had a greater birth weight and gestational age. Patients diagnosed with a 'uterine' cause of infertility had babies with the lowest birth weights and gestational ages. These results suggest the uterine environment is more important than sperm or egg quality.
The researchers then compared different IVF treatment types since this can affect the condition of the uterus. In standard IVF, an embryo is transferred immediately to a woman who has just undergone controlled ovarian hyperstimulation, while in IVF with a donor egg and IVF with a surrogate mother, the embryo is transferred to a 'natural' or un-stimulated uterus.
The scientists found that when a frozen embryo was transferred to an un-stimulated uterus the resulting infants born had significantly greater birth weights than those born as a result of standard IVF. The scientists question whether IVF would be more successful using 'frozen embryo transfer' to an un-stimulated uterus, but say the evidence is not robust enough so far.
The next steps in the research will examine how different causes of female infertility affect the uterine environment and how this could be used to further predict IVF success.
The study was published in the journal Fertility and Sterility.