The association between prenatal exposure to organochlorine compounds and neonatal thyroid hormone levels: a systematic review

In this systematic review, the association between prenatal exposure to organochlorine pesticides (OCPs) and neonatal thyroid hormone levels was studied. A systematic search of scientific literature was performed from the PubMed, SCOPUS and ISI web of science electronic bibliographic databases. The search strategy for the review was [(organochlorine OR “organochlorine pesticides” OR “organochlorine pollutants” OR “organochlorine pollutant”) AND (“thyroid hormone” OR triiodothyronine OR Thyroxine OR “fetal thyroid function” OR “thyroid function” OR “Thyroid Stimulating Hormone” AND “prenatal” AND “maternal exposure”)] in English sources. In this review, 305 papers (PubMed: 30; Scopus: 29; ISI: 246) were identified through an electronic database search. Twenty-seven articles were assessed for eligibility, from which 16 qualified articles were selected for the final evaluation. The most common OCP metabolites which were evaluated in order were hexachlorobenzene (HCB) (13 studies), pp-dichlorodiphenyldichloroethylene (pp-DDE) (13 studies), hexachlorocyclohexane (HCH) (10 studies) and dichlorodiphenyltrichlorethane (DDT) (eight studies). A review of the documents related to the association of prenatal exposure of OCPs with fetal or neonatal thyroid function tests provides us with heterogeneous data in this field. Factors such as differences in the studied populations and their area, ethnic and genetic background, time and rate of exposure, possible interaction of other thyroid-disrupting environmental factors and dietary intake of micronutrients such as iodine and/or selenium are considered the main limitations for making an accurate conclusion. For some OCPs including DDT, DDE, HCH and HCB, there are supporting evidences, and it is suggested that their exposure could potentially alter the fetal thyroid function and consequently impair the neurodevelopment process of the infants.