Patients undergoing in vitro fertilization (IVF) often understand the steps before an embryo transfer. However, they tend to be less familiar with the facts about embryo implantation after transfer. An embryo needs to implant in the uterine lining (endometrium) for a pregnancy to occur. Here, we discuss what happens during embryo implantation.
Embryo implantation after transfer – What happens first?
IVF is an advanced fertility treatment that includes multiple steps. The first step is ovarian stimulation. This requires the intended mother or the egg donor to take injectable fertility medications. The goal is to encourage the woman’s ovaries to produce multiple eggs. Once the eggs are mature, a fertility doctor will retrieve them as part of an outpatient procedure. The patient will receive light sedation to keep her comfortable.
The eggs then move to the IVF laboratory for fertilization. There, the embryologists combine them with sperm from the intended father or the selected sperm donor. Fertilization can occur either by placing the egg and sperm in a petri dish together or using intracytoplasmic sperm injection (ICSI). This is an advanced treatment for severe male infertility.
If the intended parents are interested in preimplantation genetic testing (PGT), this occurs on Day 5 of embryo development. After taking a safe biopsy, experts examine the cells for chromosomal abnormalities and/or specific genetic illnesses. While awaiting the test results, the embryo will be frozen and stored. The fertility doctor will then review the results to determine which embryo to thaw and transfer.
Embryo implantation after transfer occurs once the doctor places the embryo in the intended mother’s or the surrogate’s uterus.
The steps of embryo implantation
After an embryo transfer, the next two weeks see a series of important changes for the embryo, also known as a blastocyst. Here is a timeline of embryo implantation after transfer.
- Day 1 – The blastocyst’s cells continue to divide after the transfer. Additionally, the blastocyst “hatches” from its shell, a critical step for implantation.
- Day 2 – The blastocyst continues growing and begins attaching to the endometrium through a process called apposition.
- Day 3 – Implantation begins to occur as the blastocyst invades the uterine lining.
- Day 4 – The blastocyst enters the endometrial blood vessels for nourishment.
- Day 5 – Implantation is complete, and the embryo’s outer cells (the future placenta) release human chorionic gonadotrophin (hCG) into the mother’s bloodstream.
- Day 6 – Embryo development continues.
- Day 7 – The placenta forms and releases more hCG.
- Day 8 – Embryo development continues, and the placenta begins to function, as more hCG releases into the bloodstream.
- Day 9 – A home pregnancy test can often detect the levels of hCG. However, a woman may still experience a false negative during this stage. If the test is negative, the woman can take another test two days later. This is when the hCG levels should be higher.
Approximately two weeks after the transfer, the embryo undergoes gastrulation. During this exciting process, the once-identical cells of the embryo begin to specialize and take on different functions.