Iodine plays the critical role to maintain adequate and perfect neuropsychological development of fetus throughout gestation and in the two year of life of a newly born baby. During pregnancy, thyroid gland uptake iodine higher than the preconception level and the reserve of iodine in thyroid is 40 percent less than a preconception level. If there is not sufficient store of iodine in thyroid in preconception state a woman can never overcome this iodine deficiency during her pregnancy state because of increasing demand of iodine during pregnancy. This can result in a hypothyroxinaemic state (Smyth, 2006).
It is observed that maternal thyroid gets its extra demanded thyroid hormone successfully during their pregnancy in the areas with moderate to mild iodine deficiency (Zimmerman, 2009).
It takes about 13- 15 weeks to develop thyroid in fetus during gestation. In this long duration fetus rely completely on its mother’s thyroid hormone supply (Glioner, 1997; Perez-Lopez, 2007). Within the third trimester fetus become able to function its own thyroid gland but still it depends on mother’s thyroid hormone supply as its ability to produce thyroid hormones is very little (Becks and Burrow, 2000).
Moreover the only available resource of iodine for newly born infants is mother’s milk and the amount of iodine in mother’s milk is totally dependent onto maternal dietary iodine intake (NHMRC, 2009). . It was observed that the volume of thyroid gland was increased in pregnant women in iodine deficient areas. On the other side pregnant women in the area with sufficient supply of dietary iodine shows no visible change in the volume of thyroid.