Scientists find ‘assisted hatching’ results in fewer live births

Results of a UT Health San Antonio study show that assisted hatching does not improve live birth rate for infertile couples.
Results of a UT Health San Antonio study show that assisted hatching does not improve live birth rate for infertile couples.

Research from UT Health San Antonio found that assisted hatching resulted in fewer live births in recent years, especially in older women. Assisted hatching is an optional procedure used to prepare a human egg for implantation in the uterus. It is used in a procedure called in vitro fertilization (IVF).

The research was led by Jennifer Knudtson, M.D., a reproductive endocrinologist and assistant professor of obstetrics and gynecology at UT Health San Antonio. The study was printed in Fertility & Sterility, a publication of the American Society for Reproductive Medicine.

The retrospective data analysis was conducted to help clarify whether assisted hatching improves live birth and because frozen embryo transfers are becoming more common, Dr. Knudtson said.

“There has been insufficient evidence to conclude that assisted hatching improves live birth rates,” she said. Prior studies on assisted hatching used clinical pregnancy as the endpoint. “Live birth is what we looked at in this study, as the goal is to help infertile couples have children, not just to achieve pregnancy,” Dr. Knudtson said.

IVF procedure

In IVF, the human egg is fertilized by sperm in a petri dish and observed under a microscope during development. In more difficult cases, some physicians have used assisted hatching, thought to help a fertilized egg more easily attach to the uterine wall.

A fertilized egg normally develops inside a soft “shell” called the zona pellucida. Assisted hatching is a procedure that helps “crack” or slightly open, the “shell,” to provide a better chance of implantation. Through the years, there have been several techniques used to create the opening. They include using an instrument, chemical or laser to destroy a minute part of the shell.

Study results

The research team analyzed data from 15 trials from 2004 through 2013 from a large group of women whose IVF procedures were reported through the Society for Assisted Reproductive Technology Clinic (SART) Outcomes Reporting System. The researchers studied the outcomes of 151,533 IVF procedures that resulted in 52,733 live births. All of the women were implanted with their own frozen embryos. Assisted hatching was used in 70,738 of the procedures and was not used in 80,795.

The overall live birth rate in the assisted hatching group was 34.2 percent. In the group that did not receive assisted hatching, the result was 35.4 percent.

“As physicians, we offer assisted hatching in the IVF process hoping that it will increase live birth rate. Based on these results, it does not improve live birth rate in frozen embryo transfer,” Dr. Knudtson said.

“The significance of the results to infertility doctors is that they should carefully consider whether assisted hatching is the best option when using frozen embryo transfers. The overall results ― only a 1 percent difference between the assisted hatching and non-assisted hating groups ― may not make a significant clinical impact, but we may not be helping our patients as intended,” she explained.

“Since more clinics are doing frozen embryo transfers, the significance of the results to IVF patients is that assisted hatching does not seem to provide the benefit as intended and may be worse for certain patients,” she added.

“Since age is a major contributor to infertility, assisted hatching was used more often in women over age 38. In the years analyzed, women 38 and older with assisted hatching had fewer live births. And in 2013, all age groups that had assisted hatching had fewer live births,” Dr. Knudtson said. “This could be because of changes in the way assisted hatch was performed, the evolution of IVF practices or the way the eggs were frozen.” Some facilities use slow freezing while others use cryopreservation, a fast-freezing technique.

In this study, the researchers looked at statistics from several studies that have already occurred. “Prospective clinical studies are needed to further clarify whether assisted hatching is a beneficial practice in achieving live birth,” Dr. Knudtson said.

A Centers for Disease and Prevention report states 11 percent of women of reproductive age ― approximately 6.7 million women ― are unable to have a child.

Research team

Others involved in the study were Courtney Failor, M.D., Tiencheng Arthur Chang, Ph.D., HCLD, Robert Schenken, M.D., and Randal Robinson, M.D., from the Department of Obstetrics & Gynecology and Jonathan Gelfond, M.D., Ph.D., and Martin Goros, M.S., from the Department of Epidemiology & Biostatistics, all from UT Health San Antonio.

The National Center for Advancing Translational Sciences, National Institutes of Health, Grant KL2 TR001118 funded the project. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.


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