Many women and couples we speak with at Ovally worry about the number of eggs they’ll be able to retrieve for egg freezing or IVF to increase their chances of having a baby. They’re often concerned that there might not be enough eggs, but also wonder whether more eggs are always better or whether more eggs could at some point pose more risks and diminishing returns. We dug into the research that addresses these questions and concerns – as usual, your doctor will be able to advise you on your particular case, but we hope that the below provides helpful scientific context.
Let’s start with the basics – during a normal menstrual cycle, between 3-30 eggs begin to mature inside a woman’s ovaries until the most mature egg (or two, in the case of twins) is released during ovulation. This range of maturing eggs seems to be pretty variable, though most women younger than 35 have between 10-20 eggs at the start for every cycle. If you’re taking follicle-stimulating hormones as part of egg freezing or IVF, then you’re trying to get all the eggs that begin maturing that month (and possibly even more) to fully mature as if they were all ovulating. Some women have a weak response to the hormones and have few follicles that grow more slowly; others may respond very quickly with many eggs maturing.
What’s the “normal” number of eggs to respond to follicle-stimulating hormones? According to the Human Fertilisation and Embryology Authority, 70% of the 400k women that underwent IVF between 1991 and 2008 in the UK had 4-15 eggs retrieved after one cycle of follicle stimulation. If that’s the typical range, is there an “optimal” number of eggs to retrieve? The answer differs a bit by study but seems to lie somewhere between 10-19 eggs: One analysis found that 8-12 retrieved eggs had the best likelihood of leading to a live birth with the least risk of either failed fertilization (due to lower egg quality) or ovarian hyperstimulation syndrome. Another found the optimal number of eggs to be 10-15, a third 13, and the study with >400k women found it to be 15. Across a few studies, the likelihood of a live birth increased with the number of eggs up until 15 eggs but flattened out beyond 15-19 eggs.
What if I’m growing a smaller number of eggs during your stimulation cycle? One possible reason is that you’re not as responsive to the follicle-stimulating hormones, in which case your endocrinologist will likely increase the dosage. Some studies have identified a genetic variation associated with lower response to follicle-stimulating hormones. It’s also possible that you had lower ovarian reserve to begin with (i.e., fewer eggs left, often associating with aging). In some cases where patients grow few follicles and don’t respond much more to higher hormone stimulation, endocrinologists recommend several stimulation cycles with low hormone dosages, which also tend to be significantly less expensive.
What if I’m growing a really large number of eggs? The main thing to look out for is the increased risk of ovarian hyperstimulation syndrome, which your endocrinologist should be monitoring, so your hormone dose can be decreased if necessary. One patient group that typically grows a lot of eggs are those with polycystic ovarian syndrome (PCOS). However, some of those eggs can be of lower quality and fail to fertilize, likely because they’ve been exposed to higher levels of testosterone as part of PCOS.
Lastly, one caveat: The studies we cited above were all done on IVF patients, as the cohort of egg freezers is still much smaller by comparison.