Advances in freezing embryos may be one solution for reducing the risks caused by extremely high estrogen levels in pregnancies achieved through in vitro fertilization (IVF).
Women undergoing IVF are at higher risk of babies being born small for their gestational age and of experiencing preeclampsia. Now, two studies published in the June 2012 and January 2013 issues of the journal Fertility and Sterility have found that extremely high estrogen levels at the time of embryo transfer increase the risk of both conditions, and a solution may be to freeze embryos and transfer them in a later cycle.
Researchers at MGH Fertility Center found that freezing embryos of women who had excessively elevated estrogen at the time of egg retrieval and then performing the embryo transfer in a later reproductive cycle when hormonal levels were closer to those of a natural cycle significantly reduced the percentage of small newborns and eliminated the incidence of preeclampsia in a small group of patients.
Egg cells grow and mature in ovarian sacs called follicles, which release estrogen. The development of multiple maturing follicles can lead to significantly elevated estrogen levels. An MGH study published in June found that among almost 300 IVF pregnancies that resulted in the birth of a single infant from 2005 through 2010, the women whose estrogen levels right before egg retrieval were highest had significantly greater incidence of preeclampsia and of delivering small infants.
The team of resarchers then examined how a protocol for mothers at risk of ovarian hyperstimulation syndrome (OHSS) would affect risks associated with extremely high estrogen levels. They compared the outcomes of 20 patients who chose to have their embryos frozen and transferred later because of their risk of OHSS with those of 32 patients with pre-retrieval estrogen levels over 3,450 pg/mL who proceeded with fresh embryo transfer. They found that:
- Ten percent of the infants of mothers who chose embryo freezing and transfer in a subsequent cycle were small for their gestational age, compared with 35 percent of the infants of mothers who had fresh embryo transfer.
- The incidence of preeclampsia after fresh embryo transfer was almost 22 percent, but none of the patients who chose embryo freezing with later embryo transfer developed preeclampsia.
"If other centers validate our findings by following the same approach and achieving similar outcomes, we would recommend that each patient's hormonal dosage be adjusted to try and keep her estrogen levels below 3,000 pg/mL," says Anthony Imudia, M.D., of the MGH Fertility Center. "If the estrogen level exceeds this threshold, the patient could be counseled regarding freezing all embryos for transfer in subsequent cycles, when her hormone levels are closer to that of a natural cycle."
February 25, 2013
Posted by Leigh Ann Woodruff