Age may determine success of assisted-hatching method

Assisted hatching, a procedure commonly thought to improve pregnancy rates during in vitro fertilization (IVF), does not affect outcomes in most women younger than 38 years old, according to School of Medicine researchers.

The findings are available online in the journal Fertility and Sterility and will appear in its January 2010 print edition.


IVF is the process of fertilization that combines an egg and sperm in a laboratory dish to produce an embryo. The pregnancy rate after transfer of embryos into the uterus remains one of the primary barriers to the success of IVF.

Before implanting in the uterus, an embryo must emerge from an outer layer in a process called hatching. In some women, this outer layer or shell appears to harden, especially as women age.

In assisted hatching, a physician uses a delicate procedure to open the embryo’s shell to help it break loose and attach to the walls of the uterus. This practice has been widely used by clinicians in IVF since the 1990s, but previous studies of assisted hatching have been far from uniform in study design and patient population, and few have evaluated the number of live births.

“Because assisted hatching adds to the cost of IVF and theoretically increases the risk due to extra handling of the embryo, we decided to conduct a prospective, randomized trial to determine if it was beneficial in this younger group of women,” said Randall Odem, M.D., professor of obstetrics and gynecology and senior author of the study.

An average IVF cycle costs between $10,000-$12,000.

Women younger than 38 years old preparing to undergo IVF at WUSTL between April 2004 and March 2007 were offered enrollment into the study and underwent egg retrieval and IVF.

Embryologists in the IVF lab evaluated the patient’s embryos on the third day after fertilization, and the appearance of each embryo along with the thickness of its shell were measured and recorded. Women who had embryos with shells thicker than 12 microns were eligible to be randomized to either the hatching arm or the nonhatching arm of the study.

Only the embryologists knew to which study arm patients belonged. Patients who did not achieve pregnancy following the initial cycle and chose to undergo a second cycle were crossed over into the alternative study arm for their second cycle, if eligible.

No significant differences were observed between patients with assisted or unassisted hatching in the number of pregnancies (47 percent vs. 50 percent, respectively) or the number of live births (46 percent vs. 45 percent, respectively). Also, no significant differences were noted between hatched and unhatched groups in rates of spontaneous abortions, twins, chromosomal abnormalities or ectopic pregnancies.

Assisted hatching will continue to be routine care in older women undergoing IVF at the University’s Infertility and Reproductive Medicine Center, Odem said. But the study results have changed the amount of assisted hatching performed at the center in women younger than 38.

“The amount of assisted hatching we do has gone down by more than 50 percent,” he said. “We hope that other centers throughout the world will take note of these findings and also change their practices.”