Statistical analysis
The descriptive data on participant characteristics are summarized using
the mean and standard deviation for continuous variables. Counts and
proportions are used for the categorical variables. Chi-square tests
were performed to compare the categorical variables. To compare the
continuous variables among the groups, an analysis of covariance
(normally distributed variables) or a Kruskal-Wallis test (abnormally
distributed variables) were used. For multivariate analyses, logistic
regression was utilized. Crude odds ratios (OR) and adjusted ORs (aOR)
with 95% confidence interval (CI) were calculated to assess the
association between covariates and clinical outcomes. We selected the
covariates on the basis of their associations with the outcomes of
interest or a change in effect estimate of more than 10%. In the
adjusted Model: we adjusted female age at embryo transfer, infertility
duration, BMI, AFC, no. of oocyte retrieved, infertility type, protocol
in the fresh cycle, single blastocyst transfer, endometrial thickness on
the day of P administration, triple-line endometrial pattern, type of
embryo transferred, no. of transferred embryos, no. of transferrable
embryo and no. of good quality embryos transferred.
Interaction and stratified analyses were conducted according to female
age at oocyte retrieval, female age at embryo transfer, infertility
duration, infertility type, AFC, endometrial thickness on the day of P
administration, fertilization type, protocol in the fresh cycle, no. of
oocyte retrieved, no. of transferrable embryos, no. of transferred
embryos, no. of good quality embryos transferred, type of embryo
transferred, triple-line endometrial pattern and single blastocyst
transfer. Data were analyzed with the use of the statistical packages R
(The R Foundation; http://www.r-project.org;version 3.4.3) and Empower
(R) (www.empowerstates.com,X&Y solutions, inc. Boston, Massachusetts).
The level of significance was set at p < 0.05.
The type I error rate was
controlled using the Bonferroni stepdown procedure for multiple
comparisons. When Bonferroni corrections were applied, unadjustedp = 0.05; the number of tests, 5 (live birth rate, miscarriage
rate, clinical pregnancy rate, preterm birth rate, ectopic pregnancy
rate); p = 0.01 with Bonferroni correction applied [0.05÷5]).