Blastocyst culture

Blastocyst formation occurs at day 5 or day 6 after insemination. One of the greatest advantages of blastocyst culture is to determine slow growing or growth-arrested embryos which ultimately give low chance of pregnancy. In our center, to choose the best embryo having the best survival capacity, we prefer to culture zygotes until blastocyst stage and to do the transfer mostly on day 5, yielding a pregnancy rate of 65-70%

Another advantage of blastocyst transfer is the reduction of multiple pregnancies. The main reason behind this complication is the transfer of more than 1 embryo by many centers, due to an inadequate embryo selection on day 3, in order to increase pregnancy chances. In the past 7 years, our laboratory has successfully established blastocyst culture, allowing us to select the embryo with the best morphology and the best chance to implant in the uterus and to produce a healthy pregnancy.

Classifying blastocysts

The blastocyst is composed of two differentiated cell groups: the inner cell mass that will later give the fetus and the outer cell mass, or trophectoderm, which will produce the placenta and embryonic sac. To transfer the embryo with the best morphology, each blastocyst is assessed regarding:

• the development (starting from cavitation to hatching),
• the inner cell mass, and
• the trophectoderm

Score	Blastocyst development
1	Starting cavitation; volume of blastocoele <50% of the whole embryo
2	Blastocoele volume > 50% of the embryo
3	Blastocoele reaches the volume of the whole embryo
4	Blastocoele exceeds the embryo, thinning the zona pellucida
5	Hatching starts
6	Complete hatching, the embryo leaves the zona pellucida

Score	Trophectoderm quality
A	Epithelial structure with many closely attached cells
B	Epithelial structure with some loose cells
C	Epithelial structure with many loose cells

Score	Inner cell mass quality
A	Many cells packed together
B	Many cells but loosely packed
C	Few cells

5th day 5AA, top quality blastocyst		Orrange: inner cell mass (ICM) Green: trophectoderm (TE)		5th day 6AA, top quality blastocyst (the embryo start to leave the zona pellucida, ZP)