Study site
The subjects were expectant ladies enrolled in Guizhou Province from March to April 2020. Utilizing a cross-sectional examination by stratified sampling strategy, Guizhou Province was partitioned into 7 strata as indicated by Guiyang, Qiannan Prefecture, Anshun, Zunyi, Bijie, Tongren, and Liupanshui. Two public medical clinics were randomly chosen inside each metropolitan zone, while 2-3 public medical clinics were arbitrarily chosen inside each countryside zone.