Why Did I Get Fewer Eggs Than Follicles During IVF?
During IVF stimulation, follicle numbers can start to feel very important. At each ultrasound, you hear how many are growing and may begin to form an idea of how many eggs will be collected. Then egg retrieval happens, and the number can be lower than expected.
If you had ten follicles but only seven eggs were retrieved, it is natural to wonder where the other three went. The difference does not necessarily mean something went wrong. Follicles and eggs are closely connected, but they are not the same thing.
A Follicle Is Not an Egg
Follicles are small fluid-filled sacs in the ovaries where eggs develop. During IVF stimulation, fertility medication encourages several follicles to grow at the same time instead of the single dominant follicle that usually develops during a menstrual cycle. Ultrasound allows your fertility team to see and measure those follicles. However, it cannot show an egg inside each one. Doctors therefore use the number and size of the follicles, together with hormone levels, to estimate how the ovaries are responding. It is an estimate rather than a final egg count. (Source: Medical News Today)
Why Might Some Follicles Not Produce an Egg?
During egg retrieval, a needle collects fluid from the follicles so the embryology team can look for eggs. An egg may not be recovered from every follicle. (Source: Science Direct)
Follicle size can play a part. Larger, appropriately developed follicles are generally more likely to contain a mature egg, while smaller follicles may not have developed far enough by the time of retrieval. There can also be follicles from which no egg is recovered. This does not automatically mean there was a problem with the retrieval itself. The timing of the trigger injection is another important part of the process. It helps the eggs complete their final stage of maturation before collection, which is why clinics give precise instructions on when to take it.
The Number Can Change Again After Retrieval
The number of eggs collected is only one of several numbers you may hear over the next few days. Once the eggs reach the laboratory, the embryology team checks their maturity. Not every retrieved egg will necessarily be mature enough for fertilization. Of those that are mature, not all will fertilize, and not every fertilized egg will continue developing into an embryo suitable for transfer or freezing. (Source: Fertility)
Watching those numbers decrease can be difficult, particularly if you began treatment with a much higher follicle count. However, this gradual reduction is a normal in IVF, not proof that the cycle has failed.
What Does Your Egg Number Actually Tell You?
It is tempting to compare the final number with what you expected from your ultrasound appointments, but fertility specialists look at more than the difference between follicles and eggs. They will consider how your ovaries responded to stimulation, the sizes of the follicles before retrieval, how many eggs were mature, and what happened after fertilization. A lower egg count than follicle count can be disappointing, especially when you have spent days watching those follicles grow. But the ultrasound was never a promise of how many eggs would be collected.
Sources:
Medical News Today - https://www.medicalnewstoday.com/articles/ovarian-follicle Science Direct - https://www.sciencedirect.com/topics/nursing-and-health-professions/foll... Fertility - https://www.fertility.com/en/resources/articles/how-many-eggs-are-enough...
