IVF technique linked to birth defects

The technique is used to help embryos implant

A commonly-used technique to help women conceive may increase the risks of babies being born with defects, say scientists.

Assisted hatching uses a laser or microscopic needle to make a hole or thin the membrane around embryos produced in the test tube.

This can help the developing embryo successfully implant into the lining of the womb, and produce a pregnancy.

However, a scientific study carried out by the US Center of Disease Control and Prevention (CDC) in Atlanta found that assisted hatching was associated with higher rates of "monozygotic twinning".

This is where a single, fertilised embryo splits in two at an early stage, producing a twin pregnancy.

Monozygotic twinning is more likely to produce babies with defects than the more usual form of twinning, in which two fertilised embryos implant themselves into the womb.

Age not a factor

Dr Laura Schieve from the CDC warned that her study, while not definitive, should prompt further research into the issue.

She said that in her study, women who had monozygotic twinning were far more likely to have had assisted hatching.

The risk was 1.7 times greater in cases where some of the embryos transferred had been "hatched", and nearly four times higher in cases where all of the embryos had undergone the procedure.

Professor Ian Craft uses assisted hatching

Other factors such as the age of the woman, the number of embryos transferred and previous attempts could not explain such a difference.

In the UK, only two units are licensed by the Human Fertilisation and Embryology Authority (HFEA) to offer assisted hatching to women.

And only those who have had repeated failed attempts at embryo transfer are normally offered the procedure.

One of the centres, the London Fertility Centre, uses lasers to "thin" the membrane, a far less invasive procedure than early assisted hatching techniques, which involved passing a tiny needle completely through the embryo, piercing its membrane in two separate places.

Its director, Professor Ian Craft, wants to see more research in the UK on the possible health effects of assisted hatching, but says the HFEA's restrictions are stifling this.

The research was reported in the journal Fertility and Sterility.