Effect of environmental iodine deficiency (EID) on foetal growth in Nigeria.

Methods: The maternal and cord serum thyroid parameters at term delivery (38-40 wk of gestation) were measured and correlated with the birth weights of the corresponding newborns, and the results compared between those assessed in an ID zone (Jengere region of Bassa district, Plateau State, Nigeria) and with that of non ID (Control) zone, Jos, the State capital. Results: The level of maternal and neonatal thyroid function were significantly reduced in the group with low birth weights (<2.5 kg) as compared to the level seen in normal birth weights category in both control (Jos) and ID (Jengere) regions. Both in non ID and ID regions the maternal serum thyroxine (T4), thyroxine binding globulin (TBG) and free thyroxine index (FT4I) were positively correlated (P<0.005) with BW of term babies while thyroid stimulating hormone (TSH) (P<0.005) and thyroxine binding capacity (TBK) (P<0.05) showed negative correlation. Maternal T3 and T3/T4 ratio did not show any correlation with BW in Jos, while in the ID region of Bassa the BW showed a positive correlation (P<0.005) with the maternal serum T3 and T3/T4 ratio. Cord serum analysis of the term babies revealed that the BW was positively correlated with its T4, triiodothyronine (T3), TBG, FT4I and T4/TBG ratio (Jos only) (P<0.005) in both ID region of Bassa and non ID control zone of Jos. Cord serum TSH and TBK showed negative correlation (P<0.005) with BW. Thyrotrophin releasing hormone (TRH) stimulation test revealed that mothers with small for date (SFD) babies at term were more hypothyroid compared to the level of thyroid function seen in the women delivering normal babies. Interpretation & conclusion: Maternal thyroid hormone plays a significant role in the intrauterine foetal growth and development, and the smaller babies and their corresponding mothers, in an ID affected area are functionally sub-thyroid in greater proportion due to prevailing long standing environmental iodine deficiency (EID). Maternal T3 is an important factor in the defence of foetus in ID regions.