By Andrea Rodrigo BSc, MSc (embryologist).
Last Update: 07/05/2016

The last step involved in every in vitro fertilization (IVF) procedure is the embryo transfer to the maternal uterus.

Once the embryos have been placed inside the female reproductive system, no more involvement of the fertility clinic’s staff is required, and success just hangs upon the embryos themselves.

Even though it is a simple, painless procedure that does not take too long, carrying it out properly is fundamental, as this helps boosting the chances of embryo implantation and therefore of becoming pregnant.

Number of embryos to transfer

A key decision in every in vitro fertilization procedure is that related to the number of embryos that should be placed inside the female’s uterus. According to the order #107n of the Ministry of Health of the Russian Federation, the amount of embryos that can be transferred is limited to two.

Despite this boundary established by law, if a woman undergoing the treatment wished to have three embryos transferred, she could ask the clinic’s staff for it, and their duty would be to act according to the patient’s preferences. The recipient must sign a specific written consent beforehand.

This limit regarding the number of embryos that should be transferred has been established in order to boost the chances of achieving reproductive success, whilst at the same time being careful not to increase the likelihood of having a multiple pregnancy, as this type of pregnancy entails greater risks not only for the mother, but also for the babies.

The final decision regarding how many embryos to transfer will be made by consensus between the fertility specialists and the intended parents, keeping in mind factors such as the following:

  • Embryo quality
  • Causes of infertility
  • Age of the patient
  • Characteristics of the IVF laboratory
  • Endometrial receptivity
  • Number of viable embryos available
  • Efficiency of embryo cryopreservation systems

Depending on the above listed factors, as well as considering the benefit-risk equation, (risk of multiple births, benefits related to pregnancy), the number of embryos that should be transferred will be determined.

Endometrial receptivity

To boost embryo implantation chances and therefore let your IVF cycle be a successful one, the uterine cavity should be prepared for the moment when the embryos arrive. Embryo transfers are scheduled for the very moment when the endometrium is at its receptive phase.

In order for the endometrium, i.e. mucous membrane of the uterus, to acquire a receptive phenotype that allows embryo implantation, women should follow a treatment which aims for the preparation of the endometrium.

It involves the administration of hormone medications through oral, vaginal, or patch route in order to boost endometrial development. It will be monitored via ultrasound scan to see how the uterine lining develops, and the embryo transfer will be performed at the very moment when the endometrium has reached a size of 7 to 10 mm, and has acquired a triple line pattern.

Additional factors to keep in mind when carrying out an embryo transfer are:

  • Day of the transfer: Embryos are generally transferred on day 2 or 3, or on day 5-6. The embryo transfer due date will be scheduled according to aspects such as embryo quality and quantity, endometrial preparation, and the need for performing additional techniques such as PGD or not.
  • Frozen or fresh cycle: Deciding whether it is a frozen or fresh cycle is required, too. If frozen, the embryos will be transferred in prospective cycles. Nowadays, the most common method for embryo freezing and the one offering the highest embryo survival rates is embryo vitrification.
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Authors and contributors

 Andrea Rodrigo
BSc, MSc
Embryologist
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information
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