A blastocyst is a group of cells by a fertilized egg, formed early during pregnancy, almost 5 to 6 days after an egg gets fertilized by a sperm. Blastocyst implantation occurs in the uterine wall and eventually becomes an embryo and, finally, a fetus. It is the early embryo stage and is one of the vital phases that lead to pregnancy. In blastocyst, different cell layers divide and separate. They become the structures that nourish and protect the developing fetus. Blastocyst implantation is one of the vital steps in IVF (In Vitro Fertilization) treatment.
What is the Purpose of Blastocyst Implantation?
The first question that comes to people’s minds when they hear about blastocysts is: do blastocysts always implant in the uterus wall? In almost 80% to 90%, blastocyst implantation occurs to the uterus wall successfully. If a blastocyst cannot be implanted in the endometrium of a patient, pregnancy will never occur.
Hormones trigger a procedure called hatching for the implantation to be successful. Blastocysts will shed their transparent outer membrane, and hatching will start 1 to 3 days after blastocysts enter the uterus. Next, the outer layer cells of the blastocyst will attach themselves to the endometrium’s outer layer. The cells will release a sticky protein known as L-selectin, binding all the substances inside the endometrium. These outer cells will ultimately become a fetus.
Inner layer cells of the blastocyst implant deeply in the endometrium and become the placenta. The primary function of the placenta is to carry nutrients and oxygen to the growing fetus. Some cells of the placenta are also responsible for amniotic sac formation. The sac contains a protective and clear fluid surrounding the fetus while developing.
FAQ
What is the success rate of blastocyst transfer?
The success rate of blastocyst implantation is from 45% to 50% in women aged up to 30 years. This rate reduces to 35% to 40% in women aged 30 to 39 years.
What are the signs of successful implantation of blastocysts?
Almost one-third of women experience light spotting or bleeding during the implantation of blastocysts. But there is nothing to worry about as this bleeding is the first successful implantation and pregnancy sign. This blood is usually dark brown or light pink and lasts for a few hours to some days. Besides bleeding, other symptoms of successful blastocyst implantation include:
- Breast tenderness
- Lower back pain
- Mild cramps which are not painful, like the menstrual cramps
- Nausea
- Mood swings
Implantation primarily occurs at the top of the uterus. However, in some cases, the blastocysts cannot attach to the uterus top but outside it, mostly to the fallopian tube. It causes an ectopic pregnancy and later causes a miscarriage.
What is the structure of a blastocyst?
A blastocyst is a hollow cell group forming two layers. The inner layer is nearly 3 to 4 layers thick, while the outer layer is one cell thick. The blastocyst cells divide rapidly. A mature blastocyst can include 200 to 300 cells.
After the blastocyst implantation, it stays inside the uterus for many days before attaching to the inner uterine wall lining (endometrium). After 10 to 12 days of egg fertilization, the blastocysts will create an embryo. It will stay as an embryo for 9 weeks after successful implantation, and then ultimately, it becomes a fetus.
Conclusion
In the IVF treatment, doctors examine and grade the blastocysts inside a lab to decide which embryo will lead to pregnancy. They will determine the blastocyst’s quality depending on their shape, density, maturity, and cell number. 5 to 6 days after the egg fertilization, doctors will do the blastocyst implantation in the uterus.
