ObjectiveTo understand the distribution of demographic sociological characteristics and co-morbidities among primiparous and multiparous pregnant women under the China's universal two-child policy, to provide baseline data for clinical high-risk management and medical resources allocation.MethodsWe included pregnant women from 24 hospitals in 16 provinces (municipality, autonomous region) of China and collected their demographic sociological characteristics and obstetrics information by questionnaires between September 19th, and November 20th, 2016. Then, we used descriptive analysis to present the distribution of demographic sociological characteristics and pregnancy co-morbidities among primiparous and multiparous women and compared differences between groups by t test or Chi-square test.ResultsAmong 12 403 investigated pregnant women, 8 268 (66.7%) were primiparous and 4 135 (33.3%) were multiparous, with highest proportion in East (931/2 008, 46.4%) and lowest in Northeast (385/2 179, 17.7%). Multiparous women, comparing to primiparous women, were more likely to be elderly than 35 years (accounting for 30.6% vs. 6.5%), lower educated with high school or below (29.7% vs. 16.9%), occupied in physical labor or unemployed (49.2% vs. 42.5%), non-local residents (12.7% vs. 10.5%), family annual income higher than 120 thousand yuan (41.3% vs. 33.3%), pre-pregnancy body mass index≥24 kg/m2 (13.6% vs. 9.9%), history of artificial abortions (44.9% vs. 24.0%), or pregnancies≥4 times (23.8% vs. 3.1%) and were less likely to receive assisted reproductive technology (2.3% vs. 4.7%). The most common co-morbidities were gynecology disease (5.5%), thyroid disease (5.4% in all women), blood system disease (5.0%), digestive system disease (4.2%) and hepatitis B infection (2.5%). Multiparous women, comparing to primiparous women, had higher proportions with blood system disease (5.7% vs. 4.7%), hepatitis B infection (3.1% vs. 2.2%) and chronic hypertension (0.6% vs. 0.2%), but lower proportions with thyroid diseases, polycystic ovary syndrome, and immune system diseases, whose distribution also showed regional differences.ConclusionThere existed distribution differences regarding demographic sociological characteristics and co-morbidities proportions between primiparous and multiparous women. Therefore, we should improve clinical risk management and medical resources allocation based on pregnant women’s baseline and gestational characteristics.