Embryo quality can be influenced by several factors, many of them directly related to the quality of the gametes (oocytes and sperm). These factors that condition embryo quality can be internal, such as the cause of infertility; or external, where we find the ovarian stimulation protocols used in assisted reproduction techniques.
In in vitro fertilization (IVF) cycles, a controlled ovarian stimulation is performed with a hormonal treatment, whose objective is to stimulate the ovary to obtain an adequate number of oocytes to increase the probability of success.
However, it has been questioned whether these hormones administered exogenously during ovarian stimulation may have a negative effect on oocyte quality and, therefore, have an impact on embryo quality.
Provided bellow is an index with the 8 points we are going to expand on in this article.
The oocyte maturation process occurs during follicular development and is where the oocyte is provided with all the factors necessary for normal fertilization and embryo development.
For this, the oocyte has to mature both at the nucleus and cytoplasmiclevel. Any alteration of one of these two maturation processes can compromise the quality of the oocyte and, therefore, that of the future embryo.
However, oocyte maturation during ovarian stimulation protocols does not occur physiologically but is influenced by the hormonal treatments administered to achieve the development of a greater number of follicles.
Because of this, several authors have considered the possible effect of ovarian stimulation on oocyte and embryo quality.
Stimulated vs. unstimulated cycles
Studying embryos from a natural conception involves ethical and moral issues. For this reason, the approach taken in several studies to try to ascertain the effect of ovarian stimulation on embryo quality has been to compare stimulated cycles with unstimulated cycles.
In one of these studies, embryo division and embryo quality were analyzed in stimulated and unstimulated cycles. The conclusion was that the gonadotropin administration of the stimulation protocol (long protocol with GnRH agonists and FSH) was not reflected in the cleavage capacity nor in the quality of the resulting embryos compared to unstimulated cycles. However, because of the study design, it is possible that a minor impact on embryonic development could not be detected.
Another study focused on evaluating chromosomal alterations (aneuploidies) in unstimulated cycles and in cycles with moderate ovarian stimulation. The results suggest that the rate of embryonic aneuploidy is not increased with moderate ovarian stimulation in the population of young (donor) women studied compared to the unstimulated cycle. Despite this, the group of women in the study was small, so the results are not conclusive.
Different doses of gonadotropins
Some authors have chosen to study the effect of ovarian stimulation on embryo quality by comparing different stimulation protocols.
One study compared chromosomal alterations in embryos obtained after gentle ovarian stimulation with embryos obtained from conventional ovarian stimulation. While gentle stimulation resulted in a reduction in the number of available oocytes and embryos, the proportion of chromosomally normal embryos was lower after conventional ovarian stimulation. Therefore, these results may suggest that higher doses of gonadotropins may increase the proportion of aneuploidies.
However, as a greater number of embryos were obtained with conventional ovarian stimulation, the number of chromosomally normal embryos obtained per patient was similar after both stimulation protocols.
Further studies are needed to clarify the role of ovarian stimulation on embryo quality and thus support the use of a gentle or conventional stimulation protocol.
In general, it is suggested that mild ovarian stimulation protocols are associated with better-quality embryos. For this reason, although fewer oocytes are recovered with gentle ovarian stimulation, the number of good-quality embryos may be comparable to that obtained with higher doses.
The personalization of the ovarian stimulation protocol for each patient acquires great importance, also when it comes to embryo quality. Therefore, the specialist must take into account the circumstances of each patient to decide one protocol or the other, always avoiding aggressive stimulation protocols.
Assisted procreation, as any other medical treatment, requires that you rely on the professionalism of the doctors and staff of the clinic you choose. Obviously, each clinic is different. Get now your Fertility Report, which will select several clinics for you out of the pool of clinics that meet our strict quality criteria. Moreover, it will offer you a comparison between the fees and conditions each clinic offers in order for you to make a well informed choice.
A mild protocol may have certain advantages, such as the lower risk of ovarian hyperstimulation syndrome, fewer injections, and lower cost. However, gentle ovarian stimulation may also have disadvantages such as a higher cancellation rate or a lower number of surplus embryos available for vitrification.
FAQs from users
Can ovarian stimulation affect egg quality?
No. Some studies have tried to show that high doses of medication could worsen oocyte quality, but this has not been proven.
It is true that patients with low ovarian reserve usually take high doses of medication and have poor oocyte quality. This poor oocyte quality is associated with the low ovarian reserve, not with the doses of medication.
Are IVF embryos of poorer quality than those obtained from natural conception?
Embryos from natural conception cannot be analyzed due to the ethical and moral implications that this implies. Therefore, several authors have chosen to compare embryos obtained after stimulated and unstimulated IVF cycles.
The results were that the quality of the embryos seems similar in both study groups, although more studies are needed to confirm this.
If you want to learn more about ovarian stimulation, you can visit the following link: What is ovarian stimulation - Process, medications, and symptoms.
If you want to continue reading in-depth about embryo quality, we recommend you to read this article: Embryo quality for embryo transfer or embryo freezing
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