Embryo freezing has become common practice, and we have been doing it successfully for more than thirty years. Previously, the technique used for embryo freezing utilized computerized freezers with “slow freeze” technology. These were relatively inefficient, and a frozen embryo transfer cycle had lower success rate when compared to a “fresh” transfer, probably because of less than optimal embryo survival after slow freezing. The advent of vitrification and culturing embryos for 5 or 6 days before freezing (in the blastocyst stage) have changed things dramatically.
Historically, embryo freezing was offered only to patients with excess embryos. We used to transfer multiple embryos and freeze any “leftovers.” There are now newer indications for freezing all the embryos.
Current Indications for Embryo Freezing
Prevention of ovarian hyperstimulation syndrome (OHSS). OHSS is a potentially serious complication of in vitro fertilization (IVF). OHSS is more severe and lasts longer in pregnant patients. One of the ways of preventing severe OHSS is to freeze all the embryos and then transfer them in a subsequent month when things have settled down. At InVia Fertility Specialists, we will generally recommend freezing all embryos in patients at high-risk for severe OHSS (e.g. high estradiol levels, many eggs retrieved)
Premature rise in progesterone level. It has now been shown that if there is a premature rise in progesterone levels on day of hCG trigger, the pregnancy rates are reduced. Premature rise in progesterone leads to “advancing” the uterine lining so that it is not receptive on the day of embryo transfer. Freezing all the embryos and transferring them in a subsequent cycle results in normalizing success rates.
When embryos are biopsied for preimplantation genetic screening or diagnosis (SMART IVF). This has been discussed in a previous blog.
Slow growing embryos. Embryos that are dividing “normally” will reach the blastocyst stage five days after egg retrieval. There, however, are slow growing embryos that will reach the blastocyst stage 6 or even 7 days after egg retrieval. Dr. Richard Scott has shown that fully expanded day 5 or day 6 blastocysts have similar success during frozen embryo transfer cycles, whereas the pregnancy rate with day 6 blastocysts in fresh cycles is reduced.
Some centers routinely freeze all embryos and only do frozen embryo transfers. Shapiro et al. routinely freeze all embryos and at their Center in Nevada. They have demonstrated a significantly higher pregnancy rate with frozen when compared to fresh embryo transfer cycles. The rationale for this is that the uterine lining is more “physiological” and therefore more receptive during a frozen embryo transfer. Also, in frozen embryo transfer cycles, the transfer date can be postponed if the endometrial thickness is inadequate. In fresh cycles, the lining is exposed to very high levels of estrogen and there have been studies showing the lining to be not receptive (“out of phase”) in 25% of patients. Babies born with frozen embryos have been shown to weigh more and there is less incidence of prematurity and intrauterine growth retardation compared to “fresh” transfers. All this is consistent with the hypothesis that the uterine lining is more receptive in frozen transfer cycles.
Presence of fluid in the uterus on day of embryo transfer. This is a relatively unclear indication. If the fluid is from a dilated tube (hydrosalpinx), it has a toxic effect on the embryos and also makes the uterine lining less receptive. Most IVF programs will remove or interrupt a hydrosalpinx before starting an IVF cycle.
Dr. Karande is Board Certified in the specialty of Obstetrics and Gynecology as well as the subspecialty of Reproductive Endocrinology and Infertility. He is a Fellow of the American College of Obstetricians and Gynecologists and Member of the American Society for Reproductive Medicine.