Embryo transfer is one of the last steps in an in vitro fertilisation treatment (IVF), and is something that must not be left to chance. It is very important to make sure to make sure the endometrium, the lining of the uterus, is in a receptive condition that favours implantation of the embryo. For its preparation, we have two different procedures we can use: a natural cycle or an artificial cycle.
WHAT IS AN EMBRYO TRANSFER AND HOW IS IT PERFORMED?
Once a woman’s eggs have been extracted, they are fertilised in the laboratory and one, or two, of the resulting embryos are transferred into the maternal uterus so that they can implant into the uterus and give rise to a pregnancy.
It is a quick and painless procedure that doesn’t require anaesthesia or a hospital stay. Using a fine catheter and abdominal ultrasound, the gynaecologist places the embryos into the uterus. The patient only needs to rest for 10 minutes after the procedure before they can go home and continue their normal routine, with the exception of avoiding unnecessary excess efforts.
WHY IS ENDOMETRIAL PREPARATION SO IMPORTANT?
The endometrium is responsible for embryo implantation, and as such, the desired pregnancy. Therefore, the preparation of the endometrium is just as important as achieving good quality embryos. It is obvious that to achieve pregnancy, we must obtain good embryos, but if the endometrium is not in optimal conditions for implantation, it can lead to an implantation failure or a miscarriage.
For these reasons, if the endometrium is not in the required condition, it is not recommended to perform the embryo transfer, but it is better to evaluate doing it in the next cycle. In this way can we increase the chances of success.
NATURAL OR ARTIFICIAL CYCLE: WHEN IS EACH ONE RECOMMENDED?
Frozen embryo transfers can be carried out within a natural cycle or an artificial cycle. In general terms, the main difference between these is the way in which the endometrium is prepared. The endometrium is the lining that covers the interior of the uterus, and provides a place for the embryo to attach and implant.
A natural cycle is termed as such because it uses the natural oestrogens generated by the ovaries. In contrast, an artificial cycle, the oestrogens are administered using medications. The choice of one over another will be decided by your doctor, taking into account patient preferences and characteristics, and their menstrual cycle.
EMBRYO TRANSFER IN A NATURAL CYCLE
This treatment is the least invasive, as it avoids the use of hormonal medication and takes advantage of the natural growth of the endometrium. To be able to do this, the woman must have ovarian function an ovulate in a normal way, so that she has regular menstrual cycles between 21 and 35 days.
The main advantage is that the who procedure is more natural as it coincides with the woman’s biological cycle. As a result there are no side effects, and it is more economical, as it is not necessary to take any type of hormonal medication (oestrogens and progesterone). Usually the transfer takes place a certain number of days after ovulation, mimicking the days that the embryo would be developing and on its way to the uterus. For example, if the frozen embryo is a 5 day blastocyst, this would be transferred into the uterus 5 days after ovulation has occurred in a natural cycle.
EMBRYO TRANSFER IN AN ARTIFICIAL CYCLE
In this procedure, certain medicines are used to be able to carry out the embryo transfer. Exogenous hormones are given: estrogens to encourage the growth of the endometrium; progesterone to facilitate the implantation of the embryo. Both allow for an artificial control of the cycle to increase the chances of achieving the pregnancy.
This technique is usually advised for women who do not ovulate, in premature ovarian insufficiency (POI) or who often have irregular cycles. Whilst it is true that is more expensive, it has the advantages of being more flexible in terms of the ultrasound controls, and allows for the planning of transfer when the patient and doctor are ready.