Frozen Blastocyst Transfer & Embryo Implantation

What is Blastocyst Culture And Transfer?

Blastocyst culture is the process of developing a fertilised embryo for 5-6 days after the fusion of an egg and sperm in the process of in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI).

This is developed inside an incubator that replicates conditions similar to the human body in a blastocyst media that provides the nutrients required for its growth. These are then graded and the best quality blastocyst is implanted into the uterus.

Let us now briefly understand what occurs after fertilisation in assisted reproductive technology (ART). Human cells typically have 46 chromosomes and this state is called diploid however, eggs and sperms have 23 chromosomes each in a state that is called haploid. When these haploid cells merge during fertilisation via IVF or ICSI, they form a diploid cell called zygote. This marks the beginning of the embryonic stage, and is followed by the formation of the embryo.

Embryonic stage constitutes the following:

Day 1 – Pronuclear stage (to check number of eggs fertilised by a sperm successfully)
Day 2 – Two- to four-celled stage (only successfully formed embryos)
Day 3 – Eight-celled stage
Day 4 – 16-celled stage called Morula
Day 5/6 – Blastocyst stage

From the initial days of ART, embryo transfer has been the popular procedure wherein it is transferred into the uterus in the eight-celled stage. However, it has now been found that upon culturing the embryo for two more days in the external media till it reaches the blastocyst stage can have better outcomes.

A blastocyst has innumerable cells forming two cell types – inner cell mass and an outer trophectoderm. The former develops into the foetus and the latter, into the placenta that will serve as the route through which the growing child will obtain its nutrition and waste is excreted. The trophectoderm also plays an important role in implantation.

There are two types of blastocyst transfer:

Fresh blastocyst transfer – Embryo developed for 5/6 days after IVF or ICSI introduced into the uterus.
Frozen blastocyst transfer – 5/6 days’ developed embryos cryopreserved and used in future cycles of the patient after adequate preparation for the