In Vitro Fertilization (IVF)

Does Freezing Embryos Affect Success Rates?

freezing embryos and impregnation rates

On occasion during an IVF cycle the doctors may decide to forego an embryo transfer with fresh embryos and freeze all the embryos for a future embryo transfer. This can cause a lot of stress for the patients as they are anxious to move forward with the embryo transfer. There are two main reasons that doctors choose to freeze all the embryos; to increase the chances of pregnancy and for the health of the patient. One common question is does freezing embryos affect success rates?

One of the major reasons that we decide to freeze all the embryos is that the lining of the uterus and the age of the embryo are not synchronized. The uterus needs to be properly prepared to accept a 5 day embryo (Blastocyst) at the proper time. If a hormone called progesterone is released too early the lining of the uterus will not be ready to accept an embryo. We measure progesterone levels during IVF stimulation and if the progesterone level is greater than 1.6, the endometrium and the embryo will not be synchronized. The endometrium will be too far advanced when the embryo is placed. In this case, we will choose to perform the egg retrieval, fertilize the eggs but freeze any healthy embryos for a future transfer. This transfer can usually occur a few weeks later on a patient’s natural cycle. Embryos that are cryopreserved have the same or an increased chance of implantation compared with fresh embryos.  In 2016, our pregnancy rates with frozen embryos was 60% for women under 35 and 45% for all women, including those women over the age of 38.

A second reason that we may choose to freeze all the embryos is to prevent a syndrome called Ovarian Hyperstimulation syndrome (OHSS). This may happen if a patient over-responds to her fertility drugs. In this situation the ovaries become enlarged and fluid can accumulate in the abdomen. Patients are watched very closely to prevent this from happening. OHSS can happen if the patients estrogen level is too high or too many eggs are retrieved. If the patient becomes pregnant after a too vigorous response to the medication, there is a higher chance of this condition occurring. Therefore, if we are concerned that this syndrome may occur, we will move forward with the egg retrieval, cancel the embryo transfer and freeze all the embryos. The patient then returns for an embryo transfer the following month after the risk for OHSS is no longer present. There is almost a !00% chance the embryos will survive the freeze.

At the Fertility Centers of New England, we monitor patients’ IVF cycles very closely to maximize pregnancy rates yet be sure the patient is safe. So, in summary, although patients are often disappointed with the need to freeze all embryos, and delay the transfer, it is important to do at times for the health of the patient and to increase pregnancy rates.

If you have more questions, please contact us.