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Pregnancy Outcomes After Fresh vs. Frozen Embryo Transfer

There’s a lot in the media, including here on FertilityAuthority, about the shift toward frozen embryo transfer in IVF. Proponents, and some studies, say transferring a vitrified, thawed embryo best mimics a natural cycle and results in higher pregnancy rates than fresh IVF transfer.

But a recent retrospective study by Weill Cornell Medical College refutes this. The researchers, looking at data from 2,191 cycles at their fertility clinic, determined that fresh blastocyst transfers and frozen-thawed blastocyst transfer have equivalent pregnancy outcomes. “While there continues to be a shift toward frozen-thawed embryo cycles in the name of improved pregnancy are perinatal outcomes, it is possible that conservative stimulation protocols with fresh transfer offer equivalent benefits.”

“There’s a really big push now, and the patients are being counseled, to freeze their embryos,” says Dr. Glenn Schattman, a fertility doctor with The Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine at Weill Cornell Medical Center. “It’s not necessarily the best thing for the patient in terms of conceiving a pregnancy. It’s done to improve the statistics,” he says.

Schattman says it’s best to stimulate patients similar to how it happens in nature, what he refers to as “physiologic stimulation.” In a natural cycle you start out with a high FSH, Schattman explains. In an IVF cycle, as the follicles start to grow, you can step down the dose of FSH you’re prescribing. “Follicles are always developing. If you keep them on the same dose of medicine, 4 or 5 days later, new follicles that are just starting out are going to start growing. And then 4 or 5 days later when that first group of follicles is really big, you’re going to be stimulating more small follicles to start growing. And those follicles make different amounts of hormones and progesterone. You can mess up the eggs and you can mess up the lining of the uterus if you don’t follow what happens in nature.”

There’s also good evidence, Schattman adds, that if you use FSH, and not LH as well, you have higher progesterone levels produced by the follicles, which will also negatively affect the lining of the uterus. “Nature has two hormones for a reason – both FSH and LH. If you’re not giving LH it’s not physiologic,” Schattman says.

“I wasn’t surprised at all what we found [in the study],” Schattman says. “We really individualize stimulation protocols for the person, and then we do very careful blood tests and sonograms for monitoring, step down the medication, like what happens in nature, and trigger when the follicles are ready. There’s no difference if you stimulate appropriately and you stimulate physiologically; fresh and frozen should be exactly the same, and they were.”

“The takeaway is, nature does things a certain way for a reason. And while I think there are some really smart people out there, I don’t think anyone can outsmart nature. I think it’s critical for the overall success of any IVF cycle that you really carefully evaluate patients, individualize treatment protocols, and follow physiologic principles to maximize the chance of a successful outcome.”


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