How many "normal" embryos to bank?
I want to make sure that I have at least one child.
Ms. Odell recently had an IVF cycle to bank embryos. Test shows two of the five embryos are normal. She asks if this is enough to give her a child.
The Pre-implantation Genetic Testing for Aneuploidies (PGT-A) tells us the number of chromosomes of an embryo. Normal embryos have 46 chromosomes. Compared with embryos without the test, PGT-A normal embryos improve the odds of IVF success in certain groups of patients. Once the sample is taken, embryos (at blastocyst stage) are frozen. It takes 7-10 days to receive the results.
From a frozen embryo to a live birth is a process of attrition: the embryo may not survive the thaw, the embryo may not implant, a pregnancy may end in a miscarriage (not reaching 12 weeks), bad things happen between 12 weeks’ gestation and delivery.
The generally accepted rates are listed below:
More than 95% of frozen embryos survive thaw.
After receiving one PGT-A normal embryo, two out of three (66%) women have positive pregnancy tests.
One in ten (10%) pregnant women lose the pregnancy before reaching 12 weeks (i.e., miscarriage). Or, 90% of the pregnant women reach 12 weeks (and beyond).
One in 30 women (3%) having a 12 weeks’ pregnancy does not have a live birth. Or, 97% of these women have a live birth.
To simplify the calculation, I assume all embryos survive the thaw (100% survival rate rather than 95%) and all 12 weeks’ pregnancies end in live births (100% live birth rate rather than 97%).
Considering the attrition in implantation and miscarriage only, one PGT-A normal embryo yields 59% (= 66% x 90%) chance of a live birth, or 41% (= 100% - 59%) chance of no pregnancy or a miscarriage. The probability of having not even one pregnancy or all miscarriages is 16% (= 41% x 41%) and 6% (= 41% x 41% x 41%) when there are two and three embryos, respectively. In other words, the probability of having at least one live birth is 84% (=100% - 16%) and 94% (=100% - 6%) when there are two or three normal embryos, respectively (see table below).
The above table applies to average IVF patients. For those who produce zero normal embryo in their first IVF attempt, the probability of pregnancy using one PGT-A normal embryo from their second attempt varies based on their age. I plan to discuss this in a different article.
Ms. Odell decided to have another cycle to bank more embryos.