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Improving Implantation of Slower Growing Embryos

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The implantation rate of slower developing blastocysts (day 5 embryos) is a result of asynchrony of the embryo and the endometrium, not the quality of the embryo, according to data presented by Reproductive Medicine Associates of NY (RMA of NY). However, the implantation rate is improved if the slower developing embryos are frozen, then thawed and transferred to a well-prepared, controlled uterine environment.

“The implantation of the embryo into the uterus is an orchestrated event. There is a very narrow window of time where the lining of the uterus will permit an embryo to attach and grow,” says Dr. Tanmoy Mukherjee, Co-director of RMA of NY. “It can be the healthiest embryo in the world, but if it isn’t implanted at the right time, you’re not going to get pregnant.”

The retrospective study included patients undergoing fresh, single embryo transfer with IVF, from 2010-2015, and compared implantation rates of slow versus normal developing embryos, under a synchronous and asynchronous endometrium. Researchers noted that premature progesterone elevation signals the onset of the window of implantation, and, “Implantation rate may be decreased if the embryo is not advanced enough to implant during the narrow window.”

“What we mean by synchrony is the embryo enters the uterine cavity at the right time for implantation to be possible. On day 14, out of a 28-day-cycle, you ovulate,” Mukherjee explains. “Conception occurs in the next 2 to 3 days, and then 2 to 3 days after that the embryo enters the uterus as a blastocyst, not a day 3 embryo, to attach and grow. That’s where this timing issue comes in. The trigger that tells the uterine lining that there’s an embryo on the way is a bump in progesterone.”

Age for age, no matter how good your embryos look, if the progesterone went up, inevitably the transfer was going to fall outside of the optimal window of implantation,” he continues.

Freezing embryos is the best way to control the window of implantation, Mukherjee says. “It allows me in the next month to properly prepare an endometrium. I will absolutely be able to control the exposure to progesterone in a very timed sequence, so I know that I’m hitting the window of implantation ideally. It improves outcomes; we’re very enthusiastic about it.”


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