Efficacy of frozen embryos

By M H Ahssan

The act of stimulating a woman's ovaries with powerful drugs and then collecting the extra eggs she produces temporarily disrupts any IVF attempt conducted shortly afterwards.

Using frozen rather than freshly collected embryos during IVF treatment reduces the risks of stillbirth and premature delivery, according to three separate studies published on Monday.

The findings, from the US, Finland and Australia, suggest the act of stimulating a woman’s ovaries with powerful drugs and then collecting the extra eggs she produces temporarily disrupts any IVF attempt conducted shortly afterwards.

The researchers said, the results argue for more IVF cycles to be completed using frozen embryos, which goes against current practice.

The most recently available UK figures show that, in 2006, 29,304 patients under 35 received IVF treatment cycles using fresh embryos, while 6,894 were treated with frozen cycles.

The new data suggests, this preponderance of fresh cycles puts IVF babies at higher risk of being born prematurely and underweight, or dying soon after birth.

The new data poses a dilemma for IVF clinics, because fresh cycles tend to be more successful at resulting in pregnancies – 31 per cent of fresh cycles in 2006 for under 35s resulted in a birth, compared with 20.1 per cent for frozen cycles.

“Frozen embryo transfers are not as successful as fresh ones in terms of getting a pregnanc,” said Allan Pacey from the University of Sheffield, who is secretary of the British Fertility Society.

“It may be that we have to balance the health of children against chances of success,” Allan Pacey added.

“In a normal IVF cycle patients have their embryo transfer while the uterus is still affected by the drugs they take to stimulate the ovaries. This allows the patient’s body to get rid of the drugs, and to grow a new endometrial lining,”said Mandy Katz-Jaffe, of the Colorado Centre for Reproductive Medicine.

In the Australian study a team lead by Professor Gordon Baker at the Royal Women’s hospital in Melbourne analysed data from all Melbourne’s fertility centres collected between 2001 and 2004.

They found 469 (11 per cent) of the 4,279 attempts using fresh embryos resulted in babies with a low birth weight (less than 2.5 kg), compared with 163 (6.5 per cent) of the 2,510 IVF cycles using frozen embryos.

Similarly, the fresh cycles had a higher proportion of babies dying within 28 days (1.87 per cent to 1.16 per cent) and more pre-term births (12.3 per cent to 9.4 per cent) - defining pre-term as earlier than 37 weeks.

“These results suggest that adverse birth outcomes of assisted reproductive therapy are associated with fresh embryo transfers,” the authors wrote.

Using frozen embryos also has benefits for the mother.

One risk posed by drugs used to stimulate the ovaries is a condition called ovarian hyperstimulation syndrome (OHSS), which can be fatal in rare cases.

At present, if patients begin to develop symptoms, fertility doctors typically abandon an IVF attempt using fresh embryos because the hormonal disruption of pregnancy can make OHSS worse.