If you're hoping to make a baby the high-tech way, 15 is the magic number.
15 eggs, that is.
To boost the chances of a live birth, fertility doctors should aim to collect about 15 eggs from a woman's ovaries in a single cycle (more than the norm in Canada), according to a report published in the journal Human Reproduction.
The study of 400,000 in-vitro fertilization cycles in Britain found the live birth rate rose as the number of eggs retrieved increased to 15, but steadily declined with 20 eggs or more.
"This is the first study to look at the association between the number of eggs and live births," said Arri Coomarasamy, co-author of the report.
Aiming for 15 eggs, instead of more, minimized the risk of ovarian hyperstimulation syndrome, or OHSS, which is associated with a high number of eggs - usually over 20, Dr. Coomarasamy added.
Up to 10 per cent of IVF patients may develop OHSS, with symptoms including edema (swelling), severe abdominal pain and respiratory distress, says Assisted Human Reproduction Canada.
The norm in young women is to collect 10 to 12 eggs per IVF treatment cycle, notes the Infertility Awareness Association of Canada. But women aged 40 to 42 on average produce less than seven eggs per cycle, according to a Chicago-based fertility centre.
While 15 eggs may be the perfect number, it doesn't offset the effects of aging. In the British study, the predicted live birth rate with 15 eggs retrieved was 40 per cent for women aged 18 to 34, compared with 16 per cent for those aged 40 and over.
That's not much better than the overall live birth rate of 12 per cent for women over 40 using IVF, according to the Canadian Fertility and Andrology Society.
Still, if you're an aspiring mom over 40, that extra 4-per-cent chance could mean the world.
Does research like this benefit couples desperate to have kids - or does it fill them with false hope?