RÉSUMÉ
OBJECTIVE: To investigate the effect of endometrial thickness(EMT)on the day of hCG administration on preg⁃nancy outcome in the fresh in vitro fertilization/intracytoplasmic sperm injection(IVF/ICSI)cycle.METHODS:A retrospec⁃tive analysis was conducted of 3601 IVF/ICSI-ET cycles between January 1,2015 and December 31,2015 in eight repro⁃ductive centers.The endometrial thickness was measured on hCG injection day and the distribution of endometrial thick⁃ness and pregnancy outcome was drawn.Patients were divided into two groups based on the EMT:group A(289 cycles,EMT<8 mm),group B(3312 cycles,EMT≥duration of pregnancy and birth weight of single gestation were compared.RESULTS:Group A had significantly lower clini⁃cal pregnancy rate(46.0% vs.55.9%,P=0.001),live birth rates(35.3% vs. 47.0%,P=0.000)and higher pregnancy loss rate(23.3% vs.15.8%,P=0.024)compared with group B,while there was no significant difference in duration of pregnan⁃cy or birth weight of single gestation.Logistic regression analyses showed that clinical pregnancy rate(aOR=1.492,P=0.001)and live birth rate(aOR=1.621,P=0.000)increased in group B compared with group A,when correcting for the women age,BMI and transfer embryo numbers.CONCLUSION:The endometrial thickness on the day of hCG administra⁃tion affects the pregnancy outcome in the fresh IVF/ICSI cycle.When EMT<8 mm,the clinical pregnancy rate and live birth rate of IVF-ET are lower,and the patient should be well informed before making the decision of em⁃bryo transfer.However,endometrial thickness on the day of hCG administration does not affect the duration of preg⁃nancy and the birth weight of the fetus.