By Sandy Hemphill, Contributing Writer, BabyMed
One of the trickiest elements in in vitro fertilization (IVF) is choosing which embryos are most likely to take hold once implanted in the womb and produce a living baby in the near future. Current embryo testing methods involve several criteria that are evaluated on days 3 to 5 after fertilization. Scientists from Stanford University have discovered that embryos with the right degree of squishiness only an hour after fertilization are most likely to produce a baby and their squishiness test is by far more accurate than current methods. With a little more study and perfection of technique, their finding is expected to improve the IVF success rate and reduce the number of multiple births often associated with IVF.
Bioengineering doctorate student Livia Yanez is the lead author of the study which involved Dr. David Camarillo, assistant professor of bioengineering at Stanford, as well as several other researchers from Stanford University School of Medicine in California and Montana State University in Bozeman. The researchers developed the study after team member Barry Behr mentioned that some fertilized eggs are squishier than others. Behr is director of the IVF laboratory at the Stanford medical school.
The research team tested their theory on mice embryos but follow-up tests on human embryos predicted with 90% accuracy which human embryos were most likely candidates for implantation.
From Fertilization to Blastocyst Embryo
When sperm meets egg, fertilization occurs and an embryo is produced. Once the embryo divides into two cells, its cells continue to divide and multiply. After five or six days, the embryo has grown to 60 to 100 cells and is said to be at the blastocyst stage, ready for implantation in a woman's uterus. The healthier the blastocyst embryo, the more likely it will successfully implant in uterine tissue and continue to grow into a viable pregnancy that produces a healthy baby.
At this time, IVF has a success rate of approximately 30%. It is common to implant more than one blastocyst during an IVF cycle with the hope that, if some don't survive, at least one of them will produce a living baby. Twins are more common in IVF than in the general population due to multiple embryos being implanted. The ideal outcome is a singleton birth because carrying twins is riskier for mothers and babies.
The Embryo Squishiness Test
The Stanford researchers used a tiny pipette to exert pressure on mice embryos an hour after fertilization. They discovered a Goldilocks effect: some embryos were very rigid, some were very squishy, but others were a bit squishy but not too much. It was these just-right in-the-middle embryos that were most likely to become blastocysts healthy enough for implantation.
These squishy embryos were evaluated for viability using measures currently in place before they were implanted into female mice with the expectation the pregnancy would progress to live births. The accuracy rate between the squishiness test (more formally referred to as the rigidity assessment) and the tradition methods were significantly different in mice and human embryos:
- 90% accuracy using squishiness test.
- 50% accuracy using traditional tests.
The squishiness test produced almost twice as many live births as the traditional evaluation methods did.
Further research revealed the human embryos that were too rigid or too soft were more likely to have genetic defects that prevented DNA repair, successful cell division, and correct chromosome alignment when cells divided. These genetic errors would make pregnancy impossible.
The researchers also discovered a gene that controls egg hardening. When a sperm penetrates an egg at the moment of fertilization, the outer layer of the egg immediately hardens to prevent penetration by more sperm. Yanez said this finding may "hint at why nonviable embryos are unsuccessful."
Sources:
Carey, Bjorn. "'Squishiness' can indicate embryo viability, Stanford researchers find."Stanford News. Stanford University, 24 Feb. 2016. Web. 17 Mar. 2016.
Yanez, Livia Z. "Human oocyte developmental potential is predicted by mechanical properties within hours after fertilization."PMC. Nature Communications / Nature Publishing Group, 24 Feb. 2016. US National Library of Medicine / National Institutes of Health. Web. 17 Mar. 2016.
"IVF Step-by-Step."University of Rochester Medical Center / Obstetrics & Gynecology / Strong Fertility Center. University of Rochester Medical Center, 2016. Web. 17 Mar. 2016.