OBJECTIVE

This study examined whether blastocysts transferred on day 5 or day 6 of embryo development, as well as positivity for anti-thyroid peroxidase antibodies, affect gestational outcomes in euthyroid women undergoing in vitro fertilisation.

METHODS

Of 428 women who underwent in vitro fertilisation assessed in this retrospective cohort study, 212 (49.5%) underwent embryo transfer on day 5 of blastulation and 216 (50.5%) on day 6. Dichotomization based on anti-thyroid peroxidase antibodies status was also performed, with 370 (86.4%) women testing negative and 58 (13.6%) testing positive. Clinical and hormonal data and rates of clinical pregnancy, miscarriage, and live births were compared between the groups.

RESULTS

When evaluating gestational outcomes based on the day of blastulation, a statistically significant difference was observed in clinical pregnancy rates [51.4% (day 5) vs. 40.7% (day 6); p=0.033]. However, there was no significant difference in the relative frequencies of miscarriages (p=1.000), live births (p=1.000), or preterm births (p=1.000). Using Cramer's V test, a weak association was found between the day of blastulation and clinical pregnancy outcomes (V2=10.7%; p=0.027). There were no statistically significant differences between the anti-thyroid peroxidase antibodies-negative and -positive groups in terms of clinical pregnancy rates (p=0.396), miscarriages (p=0.129), and live births (p=0.129).

CONCLUSIONS

Higher rates of clinical pregnancy were observed in women who underwent embryo transfers performed on day 5 compared to those on day 6. However, no effect was observed with gestational outcomes. Further, anti-thyroid peroxidase antibody positivity did not have a statistically significant impact on gestational outcomes.