One IVF cycle is usually enough

Getting specific, universally applicable statistics for an IVF cycle is challenging because the numbers are highly dependent on the woman's age and underlying fertility factors. However, we can provide some general ranges and percentages to help you understand the typical "attrition" that occurs at each stage.

D1. Average Number of Eggs After Ovarian Stimulation

The average number of eggs retrieved varies significantly by age. A good target for many clinics is to retrieve between 10 to 20 mature eggs to maximize the chances of a successful pregnancy.

    Women under 35: Typically, they can expect to have 15-20 eggs retrieved.

    Women 35-40: The average number decreases to 8-12 eggs.

    Women over 40: This number can drop to 5-10 eggs or fewer.

It's important to note that not all retrieved eggs will be mature or viable for fertilization.

D2. Average Number of Embryos After Fertilization

The fertilization rate is the percentage of mature eggs that successfully fertilize.

    The average fertilization rate is about 70-80% of mature eggs.

This means that if a woman under 35 has 15 mature eggs, she might expect around 10-12 fertilized embryos.

However, there's a further drop-off as the embryos develop. Only about 30-50% of fertilized eggs typically make it to the blastocyst stage (day 5 or 6), which is the stage most commonly used for PGT and embryo transfer.

D3. Average Number of Healthy Embryos After PGT-P

This is the most complex statistic to provide, as PGT-P is highly specific to the genetic condition being screened for. However, the outcomes of PGT-P are very similar to PGT-M (preimplantation genetic testing for monogenic diseases). The results depend on the specific gene mutation, whether it's recessive or dominant, and the couple's genetic makeup.

    For couples at risk of a recessive disorder: In this case, both parents are carriers. The statistical chance of an embryo being unaffected and healthy is 75% (25% not affected/not a carrier, 50% unaffected/carrier, and 25% affected).

    For couples at risk of a dominant disorder: In this case, one parent has the disorder. The statistical chance of an embryo being unaffected is 50%.

These percentages are based on Mendelian genetics. After PGT-P testing, a couple can expect that, on average, a certain percentage of their embryos will be deemed suitable for transfer based on their specific genetic risk. A couple with 10 embryos tested for a dominant disorder could expect to have, on average, 5 healthy embryos.

It is also common for couples to combine PGT-P with PGT-A (aneuploidy testing) to screen for both the specific genetic disorder and chromosomal abnormalities. The percentage of chromosomally normal embryos decreases with age, further reducing the number of healthy embryos available for transfer, even if they are free of the specific genetic disorder.