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Higher Pregnancy Rates in Frozen IVF Transfers

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A recent study set out to determine, “Do chromosomally normal embryos implant at a higher rate in a fresh IVF cycle or in a frozen/thaw IVF cycle?” Patients who underwent IVF with comprehensive chromosome screening (CCS) and had one or more euploid (normal) embryos for transfer from September 2010 to March 2015, were included in the study conducted by Reproductive Medicine Associates of New York (RMA of New York). The data revealed, “An optimal outcome is achieved by the performance of single embryo transfer in frozen/thaw cycles.”

“Pregnancy rates are approximately 10 percent higher in the frozen cycles, and clinical pregnancy rates are approximately nine percent higher in the frozen cycles,” says Dr. Benjamin Sandler, Co-director of RMA of New York. “Single embryo transfer reduces multiple pregnancy, and improves maternal and neonatal outcomes,” he adds.

Vitrification, a fast freeze and thaw technology, has greatly improved freezing, and as a result embryos have very good thawing rates. “The question was, ‘If we have embryos that have perfect quality or normal genetic composition, is it in the patient’s best interest to not go ahead and transfer those embryos during the stimulated cycle, and wait the subsequent month in which she’s going to be transferring the embryo in an endometrium that is not stimulated and is potentially more physiologic?’”

The researchers looked at 637 patients; 394 had a frozen single embryo transfer and 243 had a fresh transfer. The demographics of patients were very similar, so there was no selection bias.
What’s behind the findings? “The endometrium is an endocrine-dependent tissue, meaning it changes according to estrogen and progesterone levels,” Sandler says. “When you do stimulation, you are going to have higher levels of estradiol. In a natural cycle, peak levels of estradiol are going to be about 250 to 300. In a stimulated cycle you may have levels 10 times as high. And in some patients you see early elevations in progesterone which can alter the timing of window of implantation.”

With a frozen cycle, the physician synthetically controls the endometrium. By mimicking a natural cycle, you don’t have worry about early progesterone elevation, and the patient is given just enough estrogen to give her a peak level of estradiol that is similar to the natural cycle, Sandler explains.


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