PFC Embryologists Publish Key Findings on the Timing of Embryo Hatching and Pregnancy Rates

Posted on March 19, 2015 by Inception Fertility

Pacific Fertility Center embryologists have, for the first time, described the effect of active embryo expansion and contraction on embryo hatching and pregnancy rates after in vitro fertilization.

Using time-lapse video imaging and high resolution microscopy, the expansion and contraction of embryos prior to implantation was observed. Frozen embryos that fail to re-expand in volume by 20-50 percent in the first 2 hours after thawing result in significantly lower rates of ongoing pregnancy, according to study results published in the February issue of Fertility and Sterility. The paper was co-authored by Sergio Vaccari, PhD, senior embryologist at Pacific Fertility Center (PFC), and Joe Conaghan, PhD, PFC lab director.

Previous evidence had suggested that vitrification (embryo freezing) might alter the physical properties of the embryo’s outer membrane (zona pellucida-ZP). However, no previous study had examined its impact on the hatching ability of embryos at Day 5 (called blastocysts).

In the study, the researchers photographed blastocysts immediately after warming, as well as 1 and 2 hours later. In addition, they compared volume changes to transfer outcomes, observing any surplus embryos after pre-implantation screening (PGS). This allowed study of the embryos’ hatching ability and physical changes in the ZP after vitrification.

“We found that the ZP’s elasticity was significantly reduced after vitrification,” said Dr. Vaccari. Small holes were present in ZPs from previous removal of cells (biopsies) for genetic testing. Despite these holes, the embryos’ hatching was hampered. “Embryos were trapped inside for 6 to 48 hours, or they failed to escape despite good rates of re-expansion.”

By contrast, making a larger hole in the ZP allowed warmed embryos to hatch completely within 4 hours. Further, embryos that expanded in volume by at least 20 percent in the first hour or 50 percent after 2 hours resulted in significantly higher clinical pregnancy rates.

“This study suggests that aggressive assisted hatching may be beneficial for some embryos,” said Dr. Conaghan.

About Pacific Fertility Center
Pacific Fertility Center is an international destination for male and female fertility treatment and care. It provides an extensive array of fertility treatment options ranging from intrauterine insemination (IUI), intracytoplasmic sperm injection (ICSI) and in vitro fertilization (IVF) to cutting-edge technology such as vitrification and genetic testing of embryos. For more information:


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