When it comes to embryo transfer, it is a small victory to obtain embryos for transfer. However, we are not yet done with the process; We continue with the selection of the embryos and the implantation. Currently, most transfers are performed on day 3 or day 5, and it is recommended not to transfer more than two embryos at a time to minimize the risk of complications for the mother and fetus. The embryos are classified by their morphological appearance and the specialists, together with the patients, have to choose the embryos to be transferred. Usually the best quality embryos are transferred, but what happens when we don't have good quality embryos?
Embryos are classified as good, fair or bad according to their morphological appearance and the ASEBIR (Association for the Study of Reproductive Biology ) classification is used. A few years ago, ASEBIR considered it necessary to collect in a consensus document those parameters that should be considered to classify embryos in different stages of development and created a categorization that goes from A to E, with A being the best quality embryos.
types of embryos
- Category A or 1st embryo: Optimum embryo quality and maximum implantation capacity.
- Category B or 2nd embryo: Good embryo quality and high implantation capacity.
- Category C or 3rd grade embryo: Embryo of medium quality with a medium capacity for implantation.
- Category D or 4th embryo: Embryo of not very good quality with a low probability of implantation.
We do not want to go into technicalities and talk about the characteristics of each classification, we leave that to the experts, but we want to show the results of recent studies on transfers with different types of embryos.
In general, low-quality embryos are not selected for transfer or cryopreservation (freezing) and are often discarded because they are believed to have lower implantation potential and higher risk of miscarriage. But there is not enough scientific evidence to show that correlation.
What do the studies say?
An article published in August of this year, conducted at the Johns Hopkins University School of Medicine , studied 5,869 IVF (in vitro fertilization) cycles and found that the morphological quality of the embryo is not associated with low birth weight or increased risks. of SGA (small for gestational age) or LGA (large for gestational age).
Another study, conducted at the prestigious MacGill University , compared singleton pregnancy outcomes resulting from good and poor quality embryo transfers, later concluding that pregnancies resulting from poor quality embryo transfer were comparable to those from embryo transfer. a good quality embryo, as they were not associated with greater adverse obstetric or perinatal outcomes. Demographic characteristics and maternal age were similar, and although the aim of the study was to assess the obstetric and perinatal risks associated with embryo quality, pregnancy rates were found to be almost twice as high with good-quality embryos.
These findings may reassure women that although the chance of a clinical pregnancy with a single poor-quality embryo is lower than with a good-quality embryo, once a pregnancy is achieved you have similar chances of having a healthy baby.
All embryos can lead to a healthy pregnancy
Responding to one of the most frequent questions regarding the viability of the embryos, it is necessary to clarify that all the embryos that are transferred have the possibility of resulting in pregnancy. We know that statistically 1st category embryos have more possibilities, speaking of almost a 60% probability when 2 1st category embryos are transferred. The decision of which embryos to transfer lies with the specialists and the patients.
What does pregnancy depend on?
It is important to emphasize that the chances of pregnancy do not simply depend on the quality of the embryo, other factors such as age and the receptivity of the endometrium also influence the chances of getting pregnant.
From the age of 40 and with their own oocytes, pregnancy rates decrease, speaking of a maximum of 20%, that is, for every 10 women who transfer embryos, 2 manage to become pregnant.
What quality are frozen embryos?
Sometimes it is decided to cryopreserve or freeze the embryos for various reasons. The quality of the frozen embryos is the same at the time of freezing as once they are thawed, that is, they present the same morphological characteristics. It may happen that, when continuing with its development after a few hours, these characteristics change and in these cases another category is assigned to the embryo.
What is the quality of egg donation embryos?
The embryos obtained by egg donation come from the eggs of young and healthy women, so the vast majority will be grade A or B with a high probability of implantation. The pregnancy rates of In Vitro Fertilization IVF with egg donation are 57.5% according to the data published by the SEF in Spain .