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Is 15 the Magic Number in Egg Retrieval?

A recent study published online in the journal Human Reproduction found that retrieving around 15 eggs from a woman’s ovaries in a single in vitro fertilization (IVF) cycle gave a woman the best chance of a successful pregnancy and birth. Retrieving too many eggs during one cycle raised the risk of complications from fertility drugs.

The study found there was a strong relationship between live birth rates and the number of eggs retrieved in one cycle, rising with an increasing number of eggs up to about 15, leveling off between 15 and 20, and then steadily declining beyond 20 eggs. The researchers analyzed more than 400,000 IVF cycles in the United Kingdom between 1991 and 2008.

“This is the first study to look at the association between the number of eggs and live births,” said Dr. Arri Coomarasamy, one of the authors of the study and a clinical reader and consultant at the University of Birmingham (UK). “This is also the first study to devise a graph that can be used by patients and clinicians to estimate the chances of a live birth for a given number of eggs.”

The UK researchers created a mathematical graph — called a nomogram — that shows the relationship between a women’s age, the numbers of eggs retrieved and the predicted live birth rate. Patients and clinicians could use it to make decisions about the degree of ovarian stimulation required to achieve the optimum number of eggs for a live birth.

The data may be useful, but patients and clinicians should not make simplistic interpretations. In a news release, fertility researchers at the Center for Human Reproduction (CHR) in New York, NY, warned that fertility patients should not be misled into believing that every patient undergoing IVF can or should be stimulated toward the production of 15 to 20 eggs. For example, women over 40 with maximal ovarian stimulation would have trouble reaching this range, whereas young women with polycystic ovarian syndrome (PCOS) will often exceed this range, even with the mildest stimulation.

"It is not the number of eggs we worry about," says Norbert Gleicher, MD, Medical Director of CHR. "It's the patient's ovarian reserve!"

Ovarian reserve is a medical term that describes a woman’s current level of ovarian function. "Assuming that patients receive reasonable ovarian stimulation for IVF," says Dr. Gleicher, MD, "the number of retrieved eggs is only a reflection of the patients' ovarian reserve."

The CHR fertility doctors say that the ovaries cannot be stimulated toward production of a specific number of eggs.

However, the University of Birmingham’s Dr. Coomarasamy believes that doctors could combine the use of the nomogram with current methods of measuring a woman’s ovarian reserve in order to work out how much her ovaries need to be stimulated in order to retrieve 15 eggs in a safe manner.

“There are tests of ovarian reserve such as anti-mullerian hormone (AMH) and antral follicle count (AFC) which are good at predicting ovarian response and the egg yield following ovarian stimulation during IVF treatment,” Dr. Coomarasamy says. “However, AMH and AFC are not good predictors of live birth rates. 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.”