Frozen embryos raise ectopic pregnancy risk

Published Oct 21, 2003


By Maxine Frith

San Antonio, Texas - Using frozen embryos in fertility treatment raises the risk of a potentially fatal ectopic pregnancy by 17 times, researchers have found.

Scientists had thought that the risk of ectopic pregnancy was only slightly increased for frozen embryos compared with the use of "fresh" embryos. The American researchers said they had been surprised by the results and were not sure of the reason.

Alison Cook, a spokeswoman for the Human Fertilisation and Embryology Authority, which regulates fertility treatment in Britain, said the study was a "serious concern".

"We have never come across these figures before. We will be studying the research," she said.

When a woman first has IVF treatment, doctors usually transfer between one and three "fresh" test-tube embryos into the uterus.

In the past 10 years technology has meant that increasing numbers of couples are choosing to freeze some of the created embryos, giving them a chance of trying further IVF cycles if the first one fails. After the first attempt, women can use the frozen embryos without having to go through the painful process of hormone treatment, egg retrieval and fertilisation for a second, third or even fourth time.

Frozen embryo storage also allows patients having chemotherapy treatment and other women to create fertilised embryos and delay motherhood until they want to try for a family.

Doctors are becoming increasingly concerned at the effect of the freezing process on embryos. Fertility expert Lord Winston has called for more research, and warned that some women were, in effect, being experimented on before the dangers were known.

A study carried out by Lord Winston's team at the Hammersmith Hospital in west London has shown that some types of embryo freezing may alter behaviour of a gene that supresses tumours.

Delaying the transfer of embryos to a mother - another technique used in some clinics - also seemed to interfere with genes in animal experiments, he said.

The new study by scientists at Brown University in Providence, Rhode Island, presented to the annual conference of the American Society for Reproductive Medicine in Texas, has revealed more concerns.

The researchers compared 2 452 cycles of IVF using fresh embryos, with 392 using frozen transfers. They found that 1,8 percent of the fresh cycles led to an ectopic pregnancy, compared with 31,8 percent of the frozen attempts.

Dr David Keefe, the lead researcher, said: "We were surprised by the increased risk. We did not expect it to be so high and we obviously need more research."

He added: "We are not sure why this happens with frozen embryos. It could be to do with the thawing process, which may disrupt the development of the embryo and cause it to stick in the tube. At the moment we just don't know."

Ectopic pregnancy occurs when the fertilised egg fails to reach the womb and begins developing in the fallopian tube, where it has no chance of surviving.

It causes agonising pain and can be fatal for a woman if not detected early and the embryo removed. The fallopian tubes can also be permanently damaged, adding to fertility problems.

The Countess of Wessex, who is now pregnant, suffered an ectopic pregnancy, as has the actress Amanda Redman. The condition is rare in natural pregnancies.

Gillian Lockwood, from the Midlands Fertility Services clinic, said about 250 000 babies had been born through frozen embryo transfers.

She said: "Our clinical data goes back 15 years and we have been freezing embryos for the last 10 years.People are saying all kinds of serious things about frozen embryos at the moment. If these findings are true it is worrying but I think we need more research."

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