Hatching of the blastocyst is a critical step in the sequence of physiologic events ending in implantation. Failure to hatch [due to intrinsic abnormalities in either the blastocyst or zona pellucida (ZP)] may be one of many factors limiting human reproductive efficiency.
Assisted hatching (AH) involves the artificial thinning or breaching of the ZP and has been proposed as one technique to improve implantation and pregnancy rates following in vitro fertilization (IVF). An increased implantation rate following mechanical opening of the ZP (partial zona dissection-PZD) was first reported in 1990s. A randomized, prospective trial of selected assisted hatching 72 hours post-retrieval (zona drilling with acidified Tyrode’s solution) suggested an improvement in implantation rates when the procedure was selectively applied to embryos with a “poor prognosis” (based on zona thickness, blastomere number, fragmentation rates, maternal age, etc.). Since these early reports, many assisted reproductive technology (ART) programs have incorporated the use of assisted hatching in efforts to improve clinical outcomes.
The assisted hatching procedure is generally performed on day 3 after fertilization, using various methods. These include the creation of an opening in the zona (either by acidified Tyrode’s solution, with a glass microneedle, using a laser, or by a piezomicromanipulator). We use a CO2 laser for this procedure which has the advantages over other methods. These include a shorter period of time, the precision (most precise method of performing AH), and the lack of adjacent thermal injury. Artificial manipulation of the ZP has been associated with an increased risk of monozygotic twinning. Patients whose embryos are hatched are often treated with antibiotics and steroids before and after embryo transfer, exposing them to the potential risks and side effects of such treatments.
Dr. Bayrak does not suggest routine AH for all IVF patients at this time. Assisted hatching may be clinically useful in patients with a poor prognosis, including those with ≥2 failed IVF cycles, poor embryo quality and women ≥38 years of age (ASRM). Higher clinical pregnancy and implantation rates have been observed after assisted hatching.