Mayo Clinic researchers recommend embryo transfer delay for at-risk women

October 24, 2006

ROCHESTER, Minn. -- Mayo Clinic researchers have determined a method to achieve the best results for the mother's health and birth of a live baby for women who undergo in vitro fertilization who demonstrate risk of ovarian hyperstimulation syndrome. Embryo transfer into the mother's uterus is delayed after the fertilization of the mother's eggs in the laboratory, and all embryos are frozen until the mother's risk subsides naturally with time. Findings will be presented as an abstract at the American Society for Reproductive Medicine in New Orleans on Tuesday, Oct. 24.

"We take steps to minimize ovarian hyperstimulation syndrome as an issue," says Charles Coddington, M.D., Mayo Clinic reproductive endocrinologist and senior study researcher. "If we feel that there's a good chance a woman would get this syndrome, then we would recommend complete cryopreservation -- freezing -- of her embryos and waiting about a month or so to complete the embryo transfer."

Ovarian hyperstimulation syndrome occurs in approximately 5 percent of women treated with medications to prompt ovulation, the first step in the in vitro fertilization process. A small percentage of those who develop the syndrome (1 to 2 percent) may experience a life-threatening illness. After stimulation, a woman's ovaries can become highly sensitive to hormonal change and start to enlarge, sometimes to orange or grapefruit size, rather than the normal walnut size. Enlargement of ovaries can be painful, as they are surrounded by a tunic that does not allow stretching. The stretched ovaries also secrete fluid into the abdomen, giving the woman a feeling of fullness, which may cause difficulty breathing. Because the fluid has left the vascular system, in a small number of cases, the woman may develop problems with the kidneys or with thrombosis. In extreme cases, blood clots can form in the legs, which can lead to pulmonary embolism.

In this study, the investigators retrospectively analyzed the medical records of 1,002 Mayo Clinic patients who had undergone in vitro fertilization between 2000 and 2004. They found 188 patients at risk for ovarian hyperstimulation syndrome, represented by high estradiol (estrogenic hormone) levels and the development of a large number of follicles in the ovaries. Three different treatment strategies were employed with the women at risk: the cycles of 21 were coasted (medication to stimulate the ovaries that is normally given daily was withheld for a day); all embryos of 32 patients were frozen, delaying transfer to the mother's uterus until the symptoms of risk subsided; and in the remaining 135 patients, with no other risk factors for ovarian hyperstimulation, physicians did not delay embryo transfer to the mother's uterus. Balancing the resulting live births with the health issues and hospitalization costs in the women who developed ovarian hyperstimulation syndrome using these three methods, the investigators found that the freezing and delaying procedure produced the best overall results.

"We conclude that elective embryo cryopreservation with subsequent embryo transfer is an effective way of preventing severe ovarian hyperstimulation syndrome and its life-threatening consequences," says Dr. Coddington. "The quality and pregnancy potential of the frozen embryos remains excellent, as demonstrated by the high cumulative live birth rate per patient."

Though women can develop an early form of this syndrome before pregnancy is achieved through in vitro fertilization like the women in this study, other women experience ovarian hyperstimulation syndrome after embryo transfer and subsequent pregnancy, and the pregnancy hormone exacerbates hyperstimulation. If the mother is pregnant, the syndrome does not pose a risk to the baby, as long as the mother remains stable, says Dr. Coddington.

What causes the syndrome and why it affects those it does are unknown, according to Dr. Coddington.
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