Study site and subjects
A hospital-based case-control study was conducted in Pingguo County, Guangxi, China.
Pingguo County is located in in the southern of China, which is an iodine-sufficient area and a suitable research site for thyroid dysfunction.
Participants were recruited from the population of pregnant women during their routine inspection in Pingguo Maternal and Child Health Hospital from May 2017 to August 2018. The hospital provides service for pregnant women and children. This study was approved by the Medical Research Ethics Committee of the local Maternity and Child Health Hospital, and all the women involved in this study gave informed consent.
Pregnant women aged 18 - 46 years who lived in Pingguo for more than 6 months and only screened in the second trimester (gestational age between 14 and 27 weeks) were invited to participate in the study. The exclusion criteria were as follows: 1) pregnant women with a history of thyroid disease, such as Christine disease; 2) pregnant women with a family history of mental retardation or organic mental disorder and dementia, hereditary endocrine and metabolic diseases, cancer, congenital malformations, and developmental dysplasia; 3) pregnant women addicted to the drugs and/or alcohol; 4) pregnant women lived in Pingguo County less than 6 months; 5) pregnant women with communicable diseases, including HIV, tuberculosis and HBV; and 6) those withholding consent to participate. In this study, 550 eligible pregnant women (gestational age ranging between 14 and 27 weeks) were recruited from May 2017 to August 2018.