IVF study has fresh hope for older women
Two embryos are better than one for maximising the chances of an IVF baby, according to one of the largest studies of success rates at fertility clinics.
Transferring two embryos raises the risk of a twin birth -- the greatest hazard in fertility treatment -- but researchers say that, for older women, the risk could be worth taking.
In the past, clinics transferred multiple embryos in the belief that this would boost the chances of a successful pregnancy and birth.
But twin and triplet pregnancies carry a higher risk of premature birth, low birth weight and other hazards.
But the study, by Professor Debbie Lawlor and colleagues at the Medical Research Council in England, found that women over 40, who have the lowest chance of having a baby, have a low risk of a multiple birth as they are less likely to carry a twin pregnancy to term.
They conclude in The Lancet that "greater freedom" should be given to clinicians and patients "to decide whether to transfer one or two embryos".
"Our findings provide some support for the transfer of two embryos in women older than 40 years, because the risks of pre-term and low birthweight were lower than those in younger women."
The researchers added that transferring three embryos should never be attempted, mainly because it increased the risk of severely premature birth.
Meanwhile, a separate study found women who get three or more embryos have no better odds of having a baby than those who get just two embryos.
"Women who have gone through infertility treatment want the best chance of having a baby, but we need to explain that the data shows transferring more embryos doesn't actually do that," said Dr Scott Nelson, of the University of Glasgow.
In Western Europe, where some countries pay for in-vitro fertilisation, or IVF, many authorities recommend a single embryo transfer for women under 37 and a maximum of two embryos for women 37 to 40. For women over 40, three is often the limit by law.
In the US, there are relatively lax guidelines and a lack of regulation. That country has seen a rise in multiple births, including the highly publicised case of Nadya Suleman, labeled the "octomom." She had octuplets in 2009 after her doctor transferred 12 embryos.