Several assisted hatching (AH) techniques, such as mechanical dissection, zona thinning with acidified Tyrode’s solution or proteolytic enzymes, and laser energy, have been evaluated with varying reports on their clinical efficacy. Now a new method of hatching, in which the zona pellucida (ZP) is mechanically expanded using hydrostatic pressure has been developed, helping to increase the implantation rates of day-3 frozen-thawed embryos in IVF/ICSI cycles. The findings of this prospective study have been published in the latest issue of Fertility and Sterility.
Cong Fang and colleagues from the First Affiliated Hospital of Sun Yat-Sen University, Guangdong, People’s Republic of China, conducted the study in subjects who had undergone their first IVF/ICSI cycles (2006-2008) to assess whether a new AH technique improves the rates of implantation and clinical pregnancy. The patients underwent thawed embryo transfer and were randomly assigned into two groups.
• AH group: Embryos were transferred after injected hydrostatic pressure was used to expand the ZP of D3 cryopreserved and thawed embryos
• No AH group (controls): ICSI needles were used to pierce the embryos, but not expand the ZP. The embryos were thus transferred without performing AH.
The two groups were comparable in terms of embryo survival:
| Parameters | AH Group | Controls |
| Number of embryos thawed | 244 | 259 |
| Number of survived embryos | 178 | 190 |
| Percentage of survived embryos | 73% | 73.4% |
The researchers, however, reported higher rates of implantation and clinical pregnancy in the AH group compared to the controls, depsite the transfer of the same number of embryos. The study concluded that mechanical expansion of the ZP is a potentially safe and effective method to improve the outcome.
It has been hypothesized that assisted reproduction outcomes may be hampered due to failure of the embryos to hatch after in vitro fertilization. Also, the ZP may be hardened or resistant to thinning owing to the embryo’s exposure to the in vitro environment, thereby affecting the process of hatching. Artificial disruption of ZP has been proposed as a tool to overcome this limitation. A recent review by Das et al (Cochrane Database of Systemic Reviews, 2009) indicated that AH has the ability to improve the clinical pregnancy rates from 25% to anywhere between 29-49%.
Besides the potential advantages, AH procedures are associated with few drawbacks, such as the enhanced risk of monozygotic twinning and damage to embryos or individual blastomeres, leading to the decrease in embryo viability. Based on existing evidence, an earlier report by the Practice Committee of the American Society for Reproductive Medicine and the Society for Assisted Reproductive Technology (Fertility and Sterility, 2008) did not support the application of assisted hatching in all IVF cycles. The report further recommends the need for customizing ART programs by selecting suitable patients, such as those with poor prognosis, who are more likely to benefit from the micromanipulation technique.
References
1. Fang C, Li T, Miao BY, Zhuang GL, Zhou C. Mechanically expanding the zona pellucida of human frozen thawed embryos: a new method of assisted hatching. Fertil Steril. 2009 Sep 25. [Epub ahead of print]
2. Balaban B, Urman B, Alatas C, Mercan R, Mumcu A, Isiklar A. A comparison of four different techniques of assisted hatching. Hum Reprod. 2002 May;17(5):1239-43.
3. Das S, Blake D, Farquhar C, Seif MM. Assisted hatching on assisted conception (IVF and ICSI). Cochrane Database Syst Rev. 2009 Apr 15;(2):CD001894.
4. Practice Committee of Society for Assisted Reproductive Technology; Practice Committee of American Society for Reproductive Medicine. The role of assisted hatching in in vitro fertilization: a review of the literature. A Committee opinion. Fertil Steril. 2008 Nov;90(5 Suppl):S196-8.
