A Systematic Review on the Risk Factors of Congenital Hypothyroidism

Congenital Hypothyroidism (CH) is the most common endocrine disorder and causes of preventable mental retardation in children. We aimed to review the reported CH-related risk factors systematically. In this review, all types of human studies on the risk factors related to the occurrence or high rate of CH were included. An electronic search was conducted in international and national electronic databases. The following keywords were used: “Congenital Hypothyroidism” AND “risk factor”. In this review, 373 papers (from PubMed: 199; Scopus: 36; ISI: 53, SID: 55, Ovid: 11; Science Direct: 19) were identified through electronic database search. A total of 98 articles were assessed for their eligibility, from which 60 qualified articles were selected for final evaluation. Most of the studies have cross-sectional, case-control, and prospective design. The current review was conducted and reported following the PRISMA (preferred reporting items for systematic reviews and meta-analyses) statement. Reported risk factors for transient CH were as follows; iodine deficiency and excess, prematurity, advanced maternal age, male gender, retinopathy of prematurity, twin pregnancy, maternal autoimmune thyroid disease, intrauterine growth retardation, and cesarean delivery. Reported risk factors for permanent CH with dysgenesis of the thyroid gland were as follows; female gender, familial history of CH, birth in geographical areas with a high rate of the disease, advanced maternal age, ethnicity (Caucasians), but not seasonality. Reported risk factors for permanent CH with dyshormonogenesis were a familial history of CH and origin of both parents from the high-risk geographical region. By using this information, we could plan more etiologic studies to investigate the pathogenesis of the disorder, design interventional studies for the known modifiable risk factors to reduce the rate of CH in our region. Also, for risk factors with limited evidence, more studies should be performed.