Assisted hatching improves implantation rates on cryopreserved-thawed embryos. A randomized prospective study.
BACKGROUND
Focus on the hatching process has so far been in the field of fresh embryos. Cryopreserved-thawed embryos have a lower rate of pregnancy than fresh embryos, which might be due to hardening of the zona pellucida.


METHODS
During a 2 year period, a prospective randomized study enrolling 253 cryopreserved-thawed cycles was performed on day 2 embryos. Pseudorandomization to assisted hatching or a control group was done on the basis of even and odd dates for thawing. One hour before embryo transfer, hatching was carried out using acidic Tyrode's solution.


RESULTS
Among 136 embryos exposed to assisted hatching, 11.4% (30) were implanted compared with only 5.8% (13) of 117 embryos not exposed to assisted hatching (P<0.05, chi(2) test). No difference in the rate of clinical pregnancy and positive serum HCG was observed between the two groups. Very few women >38 years old were included in the study, and no significant difference according to age could be found between the groups.


CONCLUSIONS
These results show that assisted hatching using acidic Tyrode's solution increases the implantation rate of cryopreserved-thawed embryos (P<0.05).
Gabrielsen
A
A
Ciconia Fertility Clinic, Aarhus, DK-8270 Højbjerg, Denmark. ag@ciconia.dk
Agerholm
I
I
Toft
B
B
Hald
F
F
Petersen
K
K
Aagaard
J
J
Feldinger
B
B
Lindenberg
S
S
Fedder
J
J
D000287:Administration, Topical; D000328:Adult; D015925:Cryopreservation; D010064:Embryo Implantation; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D007552:Isotonic Solutions / Q000008:administration & dosage* / Q000627:therapeutic use; D008297:Male; D011247:Pregnancy; D011446:Prospective Studies; D020554:Sperm Injections, Intracytoplasmic; D016896:Treatment Outcome; D015044:Zona Pellucida / Q000187:drug effects*
D007552:Isotonic Solutions; C037692:Tyrode's solution