‘Vanishing Twin’ Linked To Birth Defects In Surviving Baby
The strange “vanishing twin” phenomenon, in which only one child is born from a multiple pregnancy, has been shown to lead to an increased risk for congenital deformities in the surviving baby.
AsianScientist (Jul. 5, 2011) - The strange "vanishing twin" phenomenon, in which only one child is born from a multiple pregnancy, has been shown to lead to an increased risk for congenital deformities in the surviving baby.
This was reported today at the annual meeting of the European Society of Human Reproduction and Embryology by Prof. Michael Davies, Associate Professor and co-director of the Research Center for the Early Origins of Health and Disease at the University of Adelaide.
This "vanishing twin" phenomenon, also known as fetal resorption, may not have been easily studied with natural pregnancies, since the majority of pregnancy losses, including vanishing twins, occur in the early days and weeks of pregnancy, often before the woman even knows that she is pregnant.
However, women undergoing fertility treatment can be monitored from the moment the eggs are fertilized and transferred to the woman's womb by pregnancy tests and ultrasounds.
Davies 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 fetus had been lost by comparing routine six-week ultrasound data, which would show the presence of an empty fetal sac, and the number of babies actually delivered. These results were compared with pregnancies without any fetal loss.
Of the 7,462 babies delivered during this period, in pregnancies where ultrasound had detected an empty fetal sac at six weeks, 14.6 percent of babies born had subsequent congenital malformations. Hence, the presence of an empty sac is linked to a nearly two-fold increased risk for congenital malformation and to a nearly three-fold risk of multiple malformations in the surviving baby.
Multiple pregnancies without any fetal loss were not associated with an increase in malformations when compared with single pregnancies without fetal loss.
The associated birth defects in the surviving twin was similar for fetal losses after the first six weeks as well.
"It appears that the developmental competency or 'quality' of embryos in twins is related. Where one fails to develop, it appears to be an important indicator of the health of the survivor," said Davis.
Davis suggests that his data may be generalized to fraternal twins.
"It may be possible to generalize these results to birth defects seen in fraternal twins – twins created from two separate eggs – from spontaneous pregnancies in the general population. This is important from the point of reproductive biology," he said.
Davies believes that the same mechanism may operate in spontaneously conceived pregnancies, and may explain why a family history of miscarriage or a previous miscarriage is a risk factor for birth defects in a singleton pregnancy. These studies may also explain why both twinning and birth defects increase with maternal age.
For women who undergo fertility treatment, Davis worries that multiple embryos may compromise the embryos that survive to birth.
"Creating and using multiple embryos of lower quality may increase the risk of a developmentally compromised embryo both being selected for transfer and surviving to birth," he said.
Davis and his team intend to understand the mechanisms behind these findings, and also study whether it could be used to predict and improve embryo quality such as to drastically reduce the risk of congenital malformations in ART babies.
Source: European Society of Human Reproduction and Embryology.
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