Figure 2.

Changes in preterm birth rate, advanced maternal age , and obstetric factors associated with preterm birth according to frequency of antenatal visits in singleton pregnancies in China, 2012–18

(A) No to three antenatal care visits. (B) four to six antenatal care visits. (C) seven or more antenatal care visits. Very preterm births were during 28–31 weeks’ gestation. Moderate preterm were during 32–33 weeks’ gestation. Late preterm were during 34–36 weeks’ gestation. Preterm birth rate was adjusted according to the sampling distribution of the population.