Statistical analyses
One sample of the Kolmogorov - Smirnov test was used to test the normal
distribution of continuous variables. Continuous variables were given as
mean ± SD if normally distributed, and as median (interquartile range)
if not normally distributed. Statistical comparison was carried out by
Student’s t-test, Mann - Whitney U-test for continuous variables and
chi-square test for categorical variables, where appropriate.
Cox proportional hazard model was used to evaluate the relative
prognostic significance of female age, BMI, the number of retrieved
oocytes and the primary diagnosis of infertility in relation to CLBR.
Regression analyses were made for the individual treatment groups in all
FET cycles with transfer to evaluate the impact of independent variables
on the total LBRs from FET (n = 919).
All pregnancies within 18 months
from ovarian stimulation were analyzed, whether achieved by fresh or
frozen IVF cycle. The Kaplan-Meier method was used to calculate the
cumulative proportion of ongoing pregnancies leading to live births, and
time to pregnancy was graphically depicted by cumulative incidence
curves. The log-rank test was used to measure whether significant
differences existed in the cumulative incidence curves. Patients who did
not reach the primary outcome (live birth) including those achieved a
continuing pregnancy that did not lead to live birth were censored.
Statistical analysis was performed using the Statistical Program for
Social Sciences (SPSS Inc., Version 24.0, Chicago, USA). The two-tailed
value of P < 0.05 was considered statistically significant.