Older embryos better for IVF, says study

What a difference two days makes, at least for test-tube babies.

Once a fertilised egg is implanted in the womb, the chance of delivering a child is about 48 per cent higher if that egg is five days old instead of three, doctors in Brussels have discovered.

The research published in this week's New England Journal of Medicine found that 32 per cent of the 175 women who received the more mature eggs ultimately delivered a baby, compared with 22 per cent for the 176 who received the younger eggs.

In a journal editorial, Laura Schieve called the results "encouraging" but said the fact that the study was done in women under age 36 means the findings apply to less than half the US women receiving fertility treatments.

The new results come as fertility doctors are trying to improve the success rate for creating test-tube babies without implanting more than one embryo.

Although using multiple embryos improves the odds of success, it also increases the risk of multiple births, many of which produce children with developmental problems that can be expensive to treat.

In the United States in 2002, 35 per cent of the deliveries using test-tube technology produced twins, triplets, or more.

In Europe, the rate is about 25 per cent because doctors are more likely to implant just one embryo at a time.

The normal rate for multiple births is just 2 per cent.

The Belgian study was an attempt to improve the success rate for an individual embryo by giving it two extra days to mature.

The delay also allowed doctors to better gauge its quality.

Dr Schieve, an epidemiologist at the Centres for Disease Control and Prevention in Atlanta, told Reuters that doctors have considered that implanting the embryos at a later stage might be better because, in natural conception, the embryo usually does not attach itself to the uterus until the fifth day.

By the third day, the egg is usually still travelling down the Fallopian tube.

Until 1998, most centres did not have the right tools to grow embryos for more than three days.

"If you think of in-vitro fertilisation in stages, from stimulating egg production, to retrieving eggs, to fertilising them and transferring them, they're really good at stimulating and retrieving them, and fertilisation rates are high.

The rate-limiting step is implantation into the uterus. This is one mechanism where you might improve that," Dr Schieve said.

-REUTERS