The human egg is fertilized in the Fallopian tube, and travels towards the uterus, multiplying its cells. It reaches the uterine cavity on the third development day, and implants in the uterus between days 5 and 6 in blastocyst stage. Approximately half of the spontaneously fertilized eggs die in the tube before reaching blastocyst stage. Reproducing this process in the lab is the main objective of assisted reproduction.
The probability for my fertilized eggs of reaching blastocyst stage depends on two main factors. First, on the quality of embryos, which to a large extent depend on the age of the woman. As women age, the capacity to produce blastocysts decreases, as can be seen in figure 8. It also depends on the quality of laboratory conditions and in vitro embryo handling.
Figure 8. Blastulation rate according to age group.
As it can be seen in Figure 9, the frequency of chromosomal abnormalities in blastocysts dramatically rises with the age of woman, reaching over 75% in women 40 year or older. This determines an increase of embryo death and miscarriage due to these chromosomal abnormalities. However, normal embryos can die in the lab due to environmental conditions unsuitable to keep embryos during 5 days in culture. It is very important to keep strict quality controls in the laboratories to ensure the best conditions for long-term cultures.
Figure 9. Aneuploidy frequency in embryos according to woman’s age.
It is surprising to see that in very young women, under 34 years of age, the proportion of embryos carrying chromosomal abnormalities is almost 50%. This is due, in part, to the fact that many women in that age category are infertile precisely because they produce more embryos with chromosomal abnormalities than other healthy women of that age.
As seen in Figure 10, the frequency of chromosomal abnormalities (aneuploidy) in egg donors, that is, in very young supposedly healthy women who donate eggs, is lower than in those requiring assisted reproduction procedures to achieve a pregnancy.
Figure 10. Frequency of embryo aneuploidy according to woman’s age. RLA 2017-2020.
The Latin American Registry of Assisted Reproduction (RLA) thanks the 204 institutions accredited by REDLARA which, every year, report their data to RLA.
This voluntary and rigorous contribution makes it possible to generate a powerful database, which helps doctors and patients take decisions based on the best existing regional evidence.
This educational portal is the result of a collaborative activity between the Latin American Network of Assisted Reproduction (REDLARA), and University Diego Portales from Chile, which allow the link between the reproductive science and technology advances with the needs of people suffering from infertility and other forms of reproductive impairments.
We thank Dr. Ariel Ahumanda and Dr. Gustavo Martínez from Argentina for: images and videos of spontaneous in vitro fertilization, ICSI and PGT,
Dr. Roger Molinas from Paraguay for: videos of follicular aspiration and embryo transfer,
Dr. Javier Crosby from Chile for: images of different stages of in vitro embryo development,
Dr. Yasuyuki Mio from Japan for his video of in vitro embryo development.
We especially thank the industry for providing the financial support, which is so necessary to keep the Latin American registry as a pillar of this international cooperation, which today includes 16 countries and more than 200 collaborative institutions, from Mexico in the north to Chile in the far south.
