A study of more than 400,000 IVF cycles has found that doctors should aim to retrieve around 15 eggs from a woman's ovaries in a single cycle for the best chance of achieving a live birth.
The study, published in the Human Reproduction journal, found a strong link between live birth rates and the number of eggs retrieved in one cycle of in-vitro fertilization (IVF).
The live birth rate rose with an increasing number of eggs up to about 15, researchers found, but it leveled off between 15 and 20 eggs, and then steadily declined beyond 20 eggs.
Arri Coomarasamy of Britain's Birmingham University, who led the study, said the findings suggest that aiming for around 15 eggs per cycle would maximize the chances of a live birth while minimizing the risk of overstimulating the ovaries, risking a condition known as ovarian hyperstimulation syndrome (OHSS).
Infertility is a problem that affects around one in seven couples globally, experts say. Hundreds of thousands of IVF cycles are conducted each year around the world for people wanting a baby.
The process involves surgically removing eggs from the ovaries and combining them with sperm in the lab. Doctors pick the best embryos and implant them in the uterus.
Drugs often are prescribed beforehand to stimulate the ovaries to produce more eggs.
"A standard stimulation should aim for 10-15 eggs, and we believe this is what is associated with the best IVF outcomes," Coomarasamy said in a statement about his findings. "When the egg number exceeds 20, the risk of OHSS becomes high."
OHSS is an excessive response by the ovaries in response to hormone drugs administered to stimulate the production of eggs for collection for IVF cycles. It can cause abdominal pain, swelling and sometimes nausea and vomiting, and in very rare severe cases it is a life-threatening medical emergency.
Coomarasamy's team analyzed data from Britain's Human Fertilization and Embryology Authority on 400,135 IVF cycles in the UK between April 1991 and June 2008.
Because live birth rates have improved during this time, the researchers used data from 2006 to 2007 to create a predictive model they thought would best reflect current practice.
The data showed that during 2006 to 2007 the IVF success rate with 15 eggs retrieved was 40 percent for those aged 18 to 34, 36 percent for those aged 35 to 37, 27 percent for those aged 38 to 39 and 16 percent for women aged 40 and over.
Using the model, they plotted a mathematical graph, called a nomogram, which shows the relationship between women's age, the numbers of eggs retrieved and the predicted live birth rate.
Coomarasamy said doctors and patients could now use the nomogram, combined with other measures, called anti-mullerian hormone (AMH) and antral follicle count (AFC) tests, when making decisions about how much ovarian stimulation is needed to get the optimum number of eggs.
"If clinicians use AMH or AFC to estimate the egg yield, they can then use our nomogram to convert this estimated number of eggs into a predicted live birth rate, thus completing the prognostic chain to estimate the chances of what both they and the women want: a live born baby," he said.