Monday, 18 August 2008

IVF does not increase the risk of complications at birth

I recently read an interesting paper in The Lancet about birth complications in women who conceive using assisted fertilization, i.e. IVF, compared with complications in women who give birth having conceived normally.

Studies generally report a higher risk of complications at birth for babies conceived by IVF than for those conceived naturally. Women who undergo fertility treatment are far more likely to have twins or triplets than are women who conceive naturally thanks to the high number of embryos implanted, so a considerable proportion of the risks associated with IVF are in fact complications relating to multiple births.

However, the risks of complications before, during and after birth are still higher in women who conceive only a single child when undergoing assisted reproduction. For example, a meta-analysis published in the BMJ in 2007 found that singleton babies conceived with assisted reproduction were at least twice as likely to be born prematurely as babies conceived naturally, and one and a half times more likely to be born by cesarean section.

A group in Norway lead by Dr Liv Bente Romundstad has now found that the risk of perinatal complications in singleton births conceived using assisted reproduction is no worse than that of singleton births conceived naturally, suggesting that IVF techniques are more safe than previously thought.

The authors came to this conclusion by assessing 2,500 women who had given birth to at least one child who had been conceived naturally and one who had been conceived using assisted fertilization. Among these siblings, the risk of premature delivery and of small size for gestational age were not significantly higher in those conceived by assisted reproduction than in those conceived naturally. The authors suggest that the poor perinatal outcomes reported in women who conceive using IVF might not be the fault of the assisted reproduction techniques and instead might be attributable to maternal factors, such as underlying infertility.

This study is particularly interesting because researchers investigating outcomes after assisted reproduction find it hard to untangle the possible negative effects of IVF technology from other factors that might adversely affect birth outcomes. The women who use IVF tend to do so because they're having fertility problems, making them - and their birth outcomes - inherently different to women who conceive naturally.

Romundstad et al. controlled for such maternal factors by comparing IVF and natural conceived births in the same women, rather than births in two completely separate populations,. The births in either group had the same maternal baseline characteristics,
so the authors were able discern the effect of IVF.

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