Washington: The "vanishing twin" phenomenon, in which only one child is born from a pregnancy that originally starts as a multiple pregnancy, is associated with a two-fold increase in the likelihood of congenital malformations such as heart and skeletal defects and cerebral palsy in the remaining foetus, and nearly three-fold risk of multiple defects, a new research has revealed.
Michael Davies, who is an Associate Professor and co-director of the Research Centre for the Early Origins of Health and Disease at the University of Adelaide, Australia, and his team studied data from all assisted reproductive technology (ART) cycles that took place in South Australia between January 1986 and December 2002, and linked them to registry data on birth defects and cerebral palsy.
They identified cases in which a foetus had been lost by comparing routine six-week ultrasound data, which would show the presence of an empty foetal sac, and the number of babies actually delivered.
These results were compared with pregnancies that had started off as single pregnancies and which had continued without loss of the foetus.
During this period 7,462 babies were delivered. In pregnancies where ultrasound had detected an empty foetal sac at six weeks, 14.6 percent of babies born had subsequent congenital malformations.
The presence of an empty sac nearly doubled the risk of any malformation, and nearly trebled the risk of multiple malformations.
Multiple pregnancies without any foetal loss were not associated with an increase in malformations when compared with single pregnancies without loss in the infertility group.
Prof Davies also looked at pregnancy loss after the first six weeks and he found that this was associated with birth defects in the surviving twin as well.
The study will be published in the annual meeting of the European Society of Human Reproduction and Embryology.