Screening embryos may affect pregnancy chance

WOMEN may be worsening their already slim chances of getting pregnant by having embryos screened for genetic defects before implantation, new research suggests.

Up to now, preimplantation genetic screening (PGS), normally reserved for older women hoping to start a family, was thought to improve their chances of getting pregnant.

PGS involves extracting cells from early-stage embryos and screening them for chromosomal abnormalities that can prevent pregnancy.

Only embryos that pass the test are implanted in the womb. The procedure, is different from preimplantation genetic diagnosis (PGD) that looks for genetic defects that may be passed to a baby.

A fertility conference in Lyon, France, heard that women who used PGS were nearly a third less likely to get pregnant, than those who opted for conventional in-vitro fertilisation (IVF).

The study published in the New England Journal of Medicine, looked at 408 women aged 35 to 41 — a typical range for PGS use.

In the trial, 206 women undergoing IVF were given PGS and 202 were not. The doctors or women did not know which embryos had been screened.

At 12 weeks, 25% of the women in the PGS group were pregnant, whereas 37% of the control group had an ongoing pregnancy.

Women in the PGS group also had a lower live birth rate — 24%, as opposed to 35% of the control group.

One explanation for the results might be the damage caused by removing a cell from an embryo only three days old, the Dutch researchers said.

Another reason given was the cell which went under biopsy might not represent what is going on in the rest of the embryo. Because fertility clinics in Ireland do not have the diagnostic laboratories needed to genetically screen embryos, women are referred to clinics in Britain and Belgium for the test.

Laboratory manager at Human Assisted Reproduction Ireland (HARI) Dr Declan Keane said the fall in the pregnancy rate for women given PGS was significant and warranted further investigation.

Another study presented at the conference found complementary and alternative therapies can reduce the effectiveness of IVF.

A study of 818 Danish women undergoing IVF found those using complementary and alternative therapies had a 20% lower pregnancy success rate over 12 months.

Dr Keane said the HARI discouraged patients from ingesting herbal remedies because their chemical content was unknown.

The clinic, however, does not discourage patients from undergoing complementary therapies, such as massage or acupuncture.

“A lot of the complementary therapies help patients to de-stress before their fertility therapies and, therefore, they are more likely to achieve a pregnancy,” he said.

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