Understanding Embryo Aging
With the help of modern science, you can technically be “pregnant” long before your embryo transfer. This can make understanding your due date and weeks of gestation very confusing. Here’s a breakdown to help you understand how embryo aging and dating of your pregnancy works.
In a traditional pregnancy, gestational age is determined based on the day you ovulated. Fertilization and implantation of the embryo typically occur roughly two weeks later.
In the case of IVF, and specifically gestational surrogacy, pregnancy works a bit differently. The eggs that will eventually become embryos are not allowed to travel from the ovary into the fallopian tubes, and eventually into the uterus to await fertilization. Instead, they are removed, directly from the ovary before they are released. This typically happens two weeks into a woman’s typical 28 day menstrual cycle.
Those eggs are then fertilized outside of the body and allowed the begin growing. A reproductive endocrinologist closely monitors the cell multiplication over the next several days. In the case of a planned fresh embryo transfer, the eggs will be transferred into an awaiting uterus on either day 3, 5, or 6 of external development. In the case of a planned frozen embryo transfer, the embryos are typically frozen, thawed, and transferred on day 5 of development.
In the meantime, doctors will place you on a hormone therapy regimen that causes your body to mirror, or mock, where it would be in an unmedicated cycle. This process allows doctors to create the ideal environment for the embryos to implant and grow before moving forward with the transfer.
So, when you walk into the fertility clinic on transfer day, you’re already technically 2 weeks “pregnant” before the transfer even occurs. During the transfer, the doctor will migrate the embryo or embryos into your awaiting uterus. At the conclusion of the transfer you are said to be 2 weeks plus the age of the embryo pregnant. If a 5 day blastocyst was transferred, the woman will walk out of the clinic 2 weeks and 5 days pregnant.
Of course the term “pregnant” relies on the embryos actually implanting and continuing to develop, something that can’t be confirmed until your Beta, a blood pregnancy test, is completed in roughly two weeks. At the time of that test, if the result is positive, you will be somewhere between 4 and 5 weeks pregnant.