Objective: To explore the distribution of time to pregnancy in a Chinese population based on a cross-sectional design. Design: A cross-sectional population-based study. Setting: 8 provinces/municipalities in China between 2010 and 2011. Population or Sample: 25,270 couples aged 20-49 years. Methods: Multistage stratified cluster sampling strategy was utilized to recruit participants from each stratum by district, province/municipality, town/township, and village/street order. Main Outcome Measures: Time to diagnose pregnancy from 17,275 couples “at risk for pregnancy”. Results: In 7,889 couples eligible for analysis, the mean time to pregnancy was 17.2 months (standard deviation, 22.7) with a median of 9 months (25–75th percentile, 3–20 months). Women aged 20–24 years had the highest percentage of pregnancy at 3, 6, 12, and 24 months (23.9%, 42.5%, 58.5%, and 80.4%, respectively). Furthermore, 55.8% (3,413/6,116) and 79.9% (4,885/6,116) of women aged <35 years conceived within 1 year and 2 years, respectively, and the percentage increased by only 8.4% (5,399/6,116, 88.8%) in the third year. Only 30.6% (186/607) and 50.6% (307/607) of women aged ≥35 years conceived within 1 year and 2 years, respectively. Risk factors associated with time to pregnancy were older age, lower educational attainment of couples, higher annual household income, toxic exposure in men, shorter duration of cohabitation, longer menstrual cycle interval, history of abnormal pregnancy, and nullipara. Conclusions: Our study provides a comprehensive estimation of the time to diagnose pregnancy among Chinese couples of reproductive age, providing important information for policy makers, fertility clinicians, and sexual health educators.

Objective: This study aims to provide an evidence-based assessment of the benefits and harms of four transplantation methods so as to improve the superior pregnancy outcome and reduce the pregnancy rate of multiple embryos in the Mongoloid race. Design: Retrospective analysis Setting: Double Reproductive Centers of Medical University Population or Sample: 24,422 frozen-thawed embryo transfer (FET) cycles recorded from January 2015 to May 2018. Methods：A retrospective cohort study Main Outcome Measures: Biochemical pregnancy, clinical pregnancy, monozygotic twins, miscarriage, maternal complications, live birth. Results: Of the four groups, the biochemical pregnancy rate, the clinical pregnancy rate, and the live birth rate were the lowest in the C-1 group while they were the highest in the B-2 group. However, the B-2 group was accompanied with higher risks of miscarriage, maternal complications, twin births, preterm births and low birth weights. The biochemical pregnancy rates, the clinical pregnancy rates and the live birth rates in the C-2 group and B-1 group were statistically different, with different risks for monozygotic twins, miscarriages. Conclusion: Single blastocyst transplantation seems to be the best choice for all maternal ages to greatly reduce adverse neonatal outcomes. Tweetable abstract: This was a retrospective cohort study using the ART databases from two affiliated hospitals of Peking University. 24,422 frozen-thawed embryo transfer (FET) cycles recorded from January 2015 to May 2018 were selected to generate the research database which also included maternal characteristics.