IVF Natural Transfer

There are now several studies that confirm the theory that we can obtain significantly higher pregnancy rates when we freeze embryos and wait until resumption of a natural cycle to perform a transfer (about 6 weeks from egg retrieval). This is particularly important in patients who we anticipate will have a good response to ovarian stimulation (estrogen levels greater than 5000 pg/mL).

There are several reasons for improved outcomes with a natural transfer:

  • When we stimulate the growth of the oocytes (eggs), we are increasing the estrogen levels to 10-20 times higher than normal in a natural cycle. Such high estrogen levels appear to have a negative impact on the uterus which now may become out of sync with the growth of the eggs. High estrogen levels inhibit the effects of progesterone, which is the most essential hormone in the process of implantation and pregnancy.
  • Patients who have Polycystic Ovarian Syndrome (PCOS) naturally have a higher number of eggs compared to other patients. The higher number of eggs will lead to high estrogen levels by the end of IVF stimulation.
  • The risk of ovarian hyperstimulation syndrome increases with high estrogen levels, and this is also the case in patients with PCOS. In this syndrome, patients experience severe abdominal discomfort, fluid collection in the abdomen, and shortness of breath, which may require hospitalization. When we perform frozen embryo transfer, we can slightly alter the stimulation protocol and almost completely eliminate this syndrome.
  • Data suggest that children born after frozen embryo transfer are healthier and about 100 grams heavier.
  • The process of freezing and thawing the embryos is called vitrification and has been perfected: almost all the embryos that we freeze can now survive the thawing process.

The process of frozen embryo transfer involves the preparation of the uterus so that it can be aligned with the embryos that are frozen. This can be easily accomplished by administering estrogen pills for about two weeks. The embryos are thawed and transferred according to a set calendar, which is provided for the patient.

There are now several studies that confirm the theory that we can obtain significantly higher pregnancy rates when we wait and transfer the embryos in a frozen cycle. A major advantage of freezing embryos is that they can be safely stored until a woman’s normal hormonal balance is restored, which makes the uterus more receptive to the implanting embryo. Then, what is called a “Natural Transfer,” can be performed, giving a woman the highest chance of pregnancy.


To learn more about natural transfer or to schedule an appointment, please call (713)467-4488.