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New research sheds light on multiple IVF pregnancies

9 July 2007
Appeared in BioNews 415

New research into the formation of early embryos (blastocysts) shows how multiple pregnancies resulting from IVF might be explained and reduced, even those where only a single embryo has been implanted. The research was led by Dianna Payne - visiting fellow at the Mio Fertility Clinic in Yonago, Japan - and presented in Lyons, France at the annual meeting of the European Society of Human Reproduction and Embryology.

Around one in four IVF pregnancies is multiple, and while this figure is largely attributable to two or more embryos being implanted (leading to dizygotic or 'fraternal' twins), the possibility of multiple pregnancy seems to be increased by IVF even if only a single embryo is implanted (leading to monozygotic or 'identical' twins). Greater health risks, both to the mother and to the child, are associated with multiple pregnancies than are associated with single pregnancies. This has led to calls for regulation and further research, with the UK's Human Fertilisation and Embryology Authority consulting the public on a range of options which could lead to fewer multiple births.

Payne's team studied 33 surplus IVF embryos that had been donated for research. They used a digital camera attached to a microscope to photograph the embryos every two minutes, and then used computer software to assemble a film from these images and analyse the film's content. It is thought that this is the first time such a method has ever been used to study blastocyst formation.

26 of the 33 embryos developed to blastocyst stage, and all but one of these 26 blastocysts collapsed upon itself at least once. Those blastocysts undergoing bigger and/or more frequent collapses tended to die, but two of the surviving blastocysts possessed two distinct inner cell masses, while a third surviving blastocyst also possessed a possible second inner cell mass. The existence of more than one inner cell mass is associated with monochorionic/diamniotic twinning, which is the most common subtype of monozygotic (identical) twinning.

As well as substantiating the correlation between IVF and an increased likelihood of twinning, the study also points to a probable cause of this phenomenon - namely the culture (nutrient solution) in which IVF embryos are formed. Furthermore, the study points to a possible means of avoiding multiple pregnancies during IVF treatment - namely checking embryos for multiple inner cell masses, prior to implanting them in a prospective mother's uterus. It should therefore be possible in future for doctors to examine embryos, and advise IVF patients about the likelihood of multiple pregnancy.

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