Effect of iodine and iron status during pregnancy on maternal and neonatal thyroid functions: A prospective cohort study in Bope - Poddala health division

Abstract

Iodine and iron are the most common nutritional deficiencies in the world. It was reported that even mild iodine deficiency during pregnancy will affect maternal and subsequently neonatal thyroid functions and iron deficiency has multiple adverse effects on thyroid metabolism. Since iodine and iron deficiencies are common in pregnant women in Sri Lanka, its ultimate effect will be on the new bom. The aim of the study was to assess the iodine and iron status in women during pregnancy and its effects on thyroid function of the mother and the newborn. The study was carried out in the Bope-Poddala MOH division of Galle District. Four hundred and twentyfive pregnant women were enrolled and they were followed up during the course of the pregnancy until delivery. Maternal iodine and iron status was assessed using different parameters and its effect on babies was assessed by estimating neonatal urine iodine (UI) and neonatal thyroid stimulating hormone (nTSH). The median maternal UI concentration of the sample was 175.2pg/L (IQR 106.3-263.4 pg/L),126.0pg/L (IQR 74.8 - 196.4pg/L), 106.0pg/L (IQR 67.4-160.6 pg/L) in the first, second and third trimesters respectively indicating progressive reduction with the advancement of the pregnancy (p = <0.001). 41.7%mothers had insufficient UI concentration at the study entry and it was increased to 58.8% and 72.9% in the 2nd and 3rd trimesters. Median semm TSH in the 1 st trimester, 1.3 mlU/mL (IQR 0.8 - 1.8 mlU/mL) was significantly increased (p<0.001) to 1.6 mlU/mL (IQR 1.2 - 2.1 mlU/mL) at the 3rd trimester. Median vales of fT4 for 1st and 3rd trimesters were 18.0 pmol/L and 15.5 pmol/L (p=0.002) respectively. Results confirmed poor iodine nutrition by UI during pregnancy and role of iodized salt in maintaining iodine nutrition throughout pregnancy was questionable. In contrast maternal thyroid status was maintained within reference range. Regarding salt iodine content >50% of brands did not contain iodine within the recommended range and this may be a contributing factor to the poor iodine nutrition seen among pregnant women. Only 10.9% of neonates had(IQR) UIC level was 105.20 (81.25; 142.00) pg/L indicating sufficient UI level. The median neonatal TSH level was 3.55 (2.50; 6.50) mTU/mL whereas 37.7% of neonates had neonatal TSH>5.0 mlU/mL indicating moderate iodine deficiency according to WHO criteria. Neonatal UI level had significant positive correlations with maternal 3rd trimester UI (r=0.23; p<0.001) but such a significant correlation was not observed between maternal UI and neonatal TSH. Prevalence of anaemia was low in early pregnancy (4.8%) but iron deficiency was significantly high (42.1% had ferritin < 15ng/mL). Iron status was significantly improved at the end of the pregnancy, most probably due to iron supplements. It was observed that maternal iron status had no significant effect on maternal as well as neonatal thyroid functions in this sample. Although neonatal thyroid status was normal according to current reference values, it is worthwhile to assess long term effects of inadequate iodine status of mothers on the offspring. Iodine content of the salt products must be tightly regulated and manufacturing should be closely monitored. This study was performed at the Department o f Biochemistry and Nuclear Medicine Unit, Faculty of Medicine, University o f Ruhuna, Sri Lanka. The results were published in three original papers in peer reviewed journals. In addition, seven abstracts were presented in national and international forums. The thesis was defended on 17thNovember 2015. insufficient UI level (<100pg/L) and the median