Fresh or Frozen Embryos?

Embryo transfers are the final steps in an in vitro fertilization (IVF) process. IVF involves placing embryos fertilized in a laboratory in a woman’s uterus via a simple procedure that does not require general anesthesia. Two kinds of embryos may be used to complete in vitro fertilization: frozen or fresh embryos. Is one better than the other?

What are Fresh Embryo Transfers?

Fresh embryo transfers follow a woman’s IVF ovarian stimulation cycle and soon after the first egg retrieval procedure. Transfers involving fresh embryos may occur from one to six days after a successful fertilization.

One big advantage of a fresh embryo transfer is that it is a shorter process for getting pregnant (if the procedure is successful). Some disadvantages include rising hormone levels during ovarian stimulation and the possibility of a less receptive uterine lining for the purpose of embryo implantation. Some studies suggest that high estrogen levels may interfere with uterine receptivity during a fresh embryo transfer.

What are Frozen Embryo Transfers?

The term “frozen embryo transfer” is something of a misnomer because frozen embryos are thawed before they are transferred. Frozen embryos used for an IVF procedure were frozen during a previous in vitro fertilization cycle.

Advantages to a frozen embryo transfer (FET) include:

  • Prevents or eliminates late onset ovarian hyperstimulation syndrome. Some women may have a risk of experiencing OHSS following an egg retrieval and transfer procedure. Although signs of OHSS are usually mild, it can cause cysts and release of excess hormones such as progesterone and estrogen. Frozen embryo transfers allow fertility doctors to separate transfer from ovarian stimulation stress so that the chance of OHSS is significantly reduced.
  • Increases receptivity of the uterine lining to embryo implantation. An FET gives a woman’s body time to recuperate from an IVF stimulation cycle as well as the egg retrieval step. This helps make the womb’s endometrial lining more conducive to a successful implantation.
  • Allows couples to have genetic tests done if either partner has a serious hereditary disease that might be transmitted to an embryo

In addition, a few studies suggest that frozen embryo babies may be less likely to be of low birth weight and have a reduced risk of being smaller than normal for the gestational age.

A disadvantage to frozen embryo transfers involves the possibility embryos may not survive the freezing/thawing process. However, since frozen embryos have survival rates exceeding 95 percent, the risk is minimal. Also, the advanced technology used to freeze embryos–vitrification–is a “flash” freezing process that freezes embryos almost instantly to prevent damaging the delicate embryos.

Success Rates of Frozen and Fresh Embryo Transfers

A comprehensive study published in the New England Journal of Medicine found that live birth rates and pregnancy were similar among women using either frozen or fresh embryos. This research involved 3000 women undergoing in vitro fertilization who were given random assignments of receiving fresh or frozen embryos. One study found that 36 percent of women receiving frozen embryos eventually became pregnant while 34 percent receiving fresh embryos became pregnant. Live birth rates of fresh embryo women was 31 percent. Live birth rates of frozen embryo women was 34 percent. Another study included in the journal article discovered that live birth rates among frozen embryo women were 49 percent compared to fresh embryo women at 50 percent.

Polycystic Ovarian Syndrome and Frozen Embryos

Evidence indicates that women with polycystic ovarian syndrome who are having fertility problems may experience more success by using frozen embryos than fresh embryos. Fertility doctors think freezing embryos gives women with PCOS time between when eggs are removed and fertilized following hormone injections to increase production of eggs. This could create a more receptive womb environment in which embryos can develop and grow normally.

Call Viera Fertility Center today to schedule a consultation appointment with our fertility doctor if you are interested in learning more about in vitro fertilization and the use of frozen or fresh embryos.

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