The embryo is protected by a thin and soft layer (zona pellucida) in the first days of development. This protective barrier spontaneously bursts after several days so that the embryo can develop and nest in the uterus.
Assisted hatching is a microscopic technique that facilitates the breakage of the embryo’s protective membrane. We cut the embryo membrane with a laser just before transfer to the uterus.
This technique increases the chances of getting pregnant in case of abnormalities of the embryo membrane (zona pellucida).
What Is Assisted Hatching?
During IVF treatment, fertilization takes place in the lab. But as any couple that has gone through an IVF treatment knows, having a fertilized embryo does not guarantee a pregnancy. The embryo transferred has to implant itself into the endometrium and “stick” for pregnancy to occur.
Up to 85 percent of embryos transferred do not “stick.” There are theories on why this occurs, and one of those theories is that the embryo doesn’t hatch properly. This may happen because the embryo intrinsically has an unusually hard shell, or because something in the lab environment (the cultures used to keep the embryo alive, cryopreservation chemicals, etc.) has artificially interrupted the hatching process.
Assisted hatching is meant to get over whatever hurdles are preventing hatching and improve the odds of implantation (and pregnancy) success.
Laser-assisted hatching: Using a specialized laser to breach the zona pellucida is another possibility. Laser-assisted hatching allows much more control of the size of the hole created. Of all the methods, laser-assisted hatching may be the safest and most effective.
Does Assisted Hatching Improve IVF Success Rates?
The big question is, of course, is it worth it? Does assisted hatching to help you take home a baby? The answer is a bit complicated.
A Cochrane review on assisted hatching—that considered 31 studies, totaling 1,992 pregnancies and 5,728 women—found that assisted hatching just slightly improved clinical pregnancy rates. However, live birth rates did not improve.
Live birth rates are more important to consider than the clinical pregnancy rate since the goal in any fertility treatment is taking home a baby – not just getting a positive pregnancy test.
Unfortunately, most of the research on assisted hatching has only reported clinical pregnancy rates, and not live birth rates. Those that did look at live birth rates didn’t find an advantage. More research must be done.
Another study found that when assisted hatching was done on “good quality” embryos, pregnancy rates went down. The results varied depending on age group when assisted hatching was done on fair to poor quality embryos. This would imply that assisted hatching not only won’t help those with a good prognosis, but it may harm their chances of success.
Who Might Benefit From Assisted Hatching?
There is evidence that assisted hatching may improve clinical pregnancy rates with patients who:
- Have experienced two or more failed IVF cycles
- Have poor embryo quality
- Are older than age 38
Any manipulation or interference with an embryo is going to involve some risk. One possible risk to assisted hatching is that the embryo will become lethally damaged. This could occur before embryo transfer or after. In either case, pregnancy would not result.
Somewhat ironically, another risk of assisted hatching is the embryo’s natural hatching process will be thrown off and the embryo will fail to fully hatch from the zona pellucida.
Another risk of assisted hatching is twinning, specifically monozygotic twinning. Monozygotic twins are identical twins, who come from one egg and one sperm. Twinning is already increased during conventional IVF treatment, and research has found that assisted hatching my further increase that risk. While all multiple pregnancies carry risk, monozygotic twin pregnancies come with even higher risks for the mother and babies. Still, the risk of twinning is low, occurring less than 1 percent of the time.
You may be wondering if assisted hatching increases the risk of birth defects. A large retrospective study of over approximately 35,000 cycles found that the risk of congenital anomalies was not significantly increased with embryos that were manipulated with assisted hatching, compared to IVF cycles where assisted hatching did not take place.
Written by Rachel Gurevich
- Carney SK1, Das S, Blake D, Farquhar C, Seif MM, Nelson L. “Assisted hatching on assisted conception (in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI).” Cochrane Database Syst Rev. 2012 Dec 12;12:CD001894. doi: 10.1002/14651858.CD001894.pub5. https://doi.org/10.1002/14651858.CD001894.pub5
- Hammadeh ME1, Fischer-Hammadeh C, Ali KR. “Assisted hatching in assisted reproduction: a state of the art.” J Assist Reprod Genet. 2011 Feb;28(2):119-28. doi: 10.1007/s10815-010-9495-3. Epub 2010 Nov 2.
- Jwa J1, Jwa SC2, Kuwahara A3, Yoshida A4, Saito H5. “Risk of major congenital anomalies after assisted hatching: analysis of three-year data from the national assisted reproduction registry in Japan.” Fertil Steril. 2015 Jul;104(1):71-8. doi: 10.1016/j.fertnstert.2015.03.029. Epub 2015 Apr 29.
- Knudtson JF1, Failor CM2, Gelfond JA3, Goros MW3, Chang TA2, Schenken RS2, Robinson RD2. “Assisted hatching and live births in first-cycle frozen embryo transfers.” Fertil Steril. 2017 Oct;108(4):628-634. doi: 10.1016/j.fertnstert.2017.07.011. Epub 2017 Aug 30.
- T.A. Chang, J.F. Knudtson, Y.T. Su, E.S. Jacoby, R.D. Robinson, R.S. Schenken. “Efficacy of assisted hatching based on embryo quality in IVF cycles with fresh transfers.” Fertility and Sterility. September 2016,Volume 106, Issue 3, Supplement, Page e314.