The research ethics committee of Babol University of Medical Sciences approved this study (Reference number: IR.mubabol.HRI.REC1397.209). This interventional double-blinded randomized placebo controlled trial was registered with number IRCT20180417039338N3 in the Iran registry of clinical trials (IRCT). The trial was done in Babol Infertility Center from April 2019 to May 2020.
Eligibility criteria include women candidate for frozen embryo transfer, 18–40 year, BMI < 35 and FSH < 14mli/IU in early follicular phase (day 2–3), premature ovarian failure and uterine cavity complication recorded, no history of heart or liver diseases, baseline blood pressure (BP) equal to 100/60 (mmHg) or more measured before embryo transfer, patients being treated with hypotension medications, and who had not contraindication for taking nifedipine.
Those with BP equal to 100/60 (mmHg) or less for any reasons half hour before embryo transfer, patients who decline to participate the study and the ones taking medications interacting with nifedipine excluded. Before randomization, the trial protocol was fully described to the participants and informed consent was taken. Since the pregnancy rate was showed no difference using various methods of endometrial preparation pre-embryo transfer, both routine preparation protocols (the natural cycle protocol or artificial protocol) were accepted and applied .
Randomization and Intervention
Sample size was calculated according to a significance level of 0.05 and, a power level of 0.80. The minimum sample size was determined 100 women in each group and the allocation ratio into each arm was 1:1. All blocking and random allocation were performed by the University's statistics center. The statistician used an online randomization site for random block assignment. They produced a permuted block-sized numbers with block-8 and offered that to a trained nurse. The list was concealed of the principal researchers. The nurse as a third person that was not involved the study, allocated the participants to the group A or B according to the blocked numbers on the day of embryo transfer and cleaned the list immediately after the allocation.
The medicines contain 100 tablets of nifedipine 20 mg (Tolidaru co., Iran) and 100 tablets placebo that were given orally. The researcher inserted each tablet into a small uni-shape capsule and packed in the uni- shape pocket and coded A or B. 30 minutes before ET, participants’ blood pressure were taken with a digital arm BP measuring device (Microlife, Widnau, Switzerland)) and if it was 100/60 (mmHg) or more, the mentioned nurse administered the pockets A or B to the patients according to the blocked numbers. BP and possible adverse events were checked 30 minutes post-ET. The participants, the sonographer of endometer monitoring, the embryo transfer physician, and staff of the ICSI laboratory were not aware of the allocation. The nurse also recorded the details of the demographic characteristics, oocyte and embryo quality (after warming) and pregnancy outcomes of the patients according to their codes. Embryo quality was defined using a scoring system based on the cell number and regularity of blastomeres as well as the rate of fragmentation. Good quality embryo (A and B) was including stage-specific cell size, no multinucleation, and maximum 10% fragmentation according to Eshre consensus guidline 2011 . Then outcome assessor inserted the recorded data to the checklist and then to the SPSS software and analyzed.
The primary outcome was chemical pregnancy rate that was defined as serum human chorionic gonadotropic > 190 IU/L in the frozen embryo recipients) 16 days following embryo transfer were in the nifedipine group and the controls . Implantation rate was considered as the secondary outcome and defined as visualization of the gestational sac in the vaginal ultrasound image in 5–6 weeks following chemical pregnancy confirmed . Another secondary outcome was the clinical pregnancy that defined as ultrasound confirmation of fetus heartbeat after 6–8 weeks following chemical pregnancy confirmed .
Statistical tests were done using SPSS 16 (SPSS Inc., Version 18, Chicago, IL, USA). Kolmogorov-Smirnov tests applied to assess the normality of quantitative variables. Data were presented as mean and standard deviations (mean ± SD). A 2-tailed p-value of 0.05 or less was considered statistically significant. Intention-to-treat principle (ITT) was applied in the analysis.
T-test determined the mean difference of parameters between the study groups and the control.