The effect of assisted hatching on pregnancy rates after frozen embryo transfer.

OBJECTIVE

To compare clinical pregnancy and implantation rates after transfer of frozen-thawed embryos prepared according to an assisted hatching protocol or a nonassisted hatching protocol.

DESIGN

A historical cohort study in which a cohort of patients who underwent an assisted hatching protocol was matched for clinical parameters to an external historical cohort treated before assisted hatching was available.

SETTING

In vitro fertilization-ET facility of a university-based practice.

PATIENTS

Seventy-nine matched pairs.

INTERVENTIONS

Nonassisted hatching patients: embryos were thawed, cultured in human tubal fluid + 0.5% bovine serum albumin until 48 hours and transferred. Assisted hatching patients: embryos thawed, cultured in human tubal fluid + 10% synthetic serum substitute until 72 hours, had assisted hatching and transferred.

MAIN OUTCOME MEASURES

Clinical pregnancy (gestational sac) and implantation rates.

RESULTS

Twelve (15.2%) clinical pregnancies per transfer in nonhatched group versus 24 (30.4%) in hatched group. Nonhatched group: 284 embryos transferred; 15 (5.3%) implanted. Three pregnancies (25.0%) had two sacs. Hatched embryos: 269 were transferred; 37 (13.7%) implanted. Eleven pregnancies (45.8%) were multiple gestations (9 twins, 2 triplets).

CONCLUSION

Clinical pregnancy and implantation rates were higher for group having assisted hatching protocol. It is not clear whether the improvement is due to the overall methodology change or to assisted hatching. Assisted hatching using the zona-drilling technique is not detrimental to frozen-thawed human embryos and may be beneficial.