May 11, 2011
Perfect Number For IVF Success Is Fifteen
The best chance of achieving a live birth after assisted reproduction technology lies within retrieving around 15 eggs from a woman's ovaries in a single cycle, researchers found.
A study published in the medicine journal Human Reproduction found a strong relationship between live birth rates and the number of eggs retrieved in a single cycle.
Researchers analyzed over 400,000 IVF cycles in the U.K. and discovered by increasing the number of eggs to 15 the live birth rate rose and then leveled off between 15 to 20 eggs, with a steady decline occurring beyond 20 eggs.
IVF treatments involve taking eggs and fertilizing them in a lab dish with sperm. The uterus is then implanted with several early-stage embryos with hopes that one of them will result in a live birth or in some cases multiple births.
Embryos which are not immediately implanted are usually frozen, and can be thawed at a later date for IVF attempts. The data in the study did not distinguish between the live births that resulted from fresh or thawed embryos.
"Our data show that around 15 eggs may be the best number to aim for in an IVF cycle in order to maximize the chances of a live birth while minimizing the risk of ovarian hyper stimulation syndrome (OHSS) which is associated with a high number of eggs, usually over 20," author of the study Dr. Ari Coomarasamy said in a press release from the European Society of Human Reproduction and Embryology.
Previous smaller studies have been reported on the association between egg numbers and pregnancy rates, but the current study involves live births.
"Live birth" is described as an event in which at least one baby was born alive.
"This is the first study to look at the association between the number of eggs and live births," Coomarasamy said. "Some smaller studies have reported previously on the association between egg numbers and pregnancy rates, but not live births."
In addition to the best number of eggs to retrieve, the study also developed a mathematical graph called a nomogram that could be used, alongside current methods of retrieving eggs to safely stimulate a woman's ovaries in order to estimate the chances of a live birth for a given number of eggs.
He says, "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."
"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."
"Mild stimulation protocols aim to retrieve less than six to eight eggs; a standard stimulation should aim for 10-15 eggs, and we believe this is what is associated with the best IVF outcomes; when the egg number exceeds 20, the risk of OHSS becomes high," he says.
The findings showed that the rate of success for 15 eggs in 2006-2007 was about 40% among women aged 18-34, 36% for those aged 35-37, 27% for those aged 38-39 and 16% for women aged 40 and more.
Dr Coomarasamy is a Clinical Reader and Consultant in Reproductive Medicine and Surgery at the University of Birmingham (UK)
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