A team of US scientists has found that assisted hatching, a technique used in fertility clinics to help embryos implant into the womb, could increase the chance of monozygotic (identical) twins. The scientists, based at the Center for Disease Control and Prevention, Atlanta, published their results in the latest issue of the journal Fertility and Sterility.
Assisted hatching involves making a small opening in the protective lining surrounding the early embryo (the zona pellucida), either chemically or mechanically. The procedure is thought to increase the chances of success in cases where IVF (in vitro fertilisation) embryos repeatedly fail to implant into the womb lining.
The researchers examined the records of over 11,000 IVF pregnancies, to identify those in which the number of fetal heartbeats detected in an early ultrasound scan was more than the number of embryos transferred. Their results indicate that assisted hatching increases the risk of monozygotic twinning by up to four times. The authors conclude that the technique could result in an embryo with a hole in the zona pellucida, possibly causing it to split into two embryos around the time of implantation.
The scientists stress the need for further studies, but say that the benefits of assisted hatching are unclear. They also point to the increased health risks associated with multiple births, particularly identical twins. Professor Ian Craft, director of the London Fertility Centre in the UK, told BBC News Online that he wants to see more research on the possible health effects of the technique.
Sources and References
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IVF technique linked to birth defects
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Does assisted  hatching pose a risk for monozygotic twinning in pregnancies conceived through in vitro fertilisation.
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