Check if the salt you use is iodized.
"Iodine levels in the US have been decreasing, which has the potential to negatively impact the mother and unborn child," said Stagnaro-Green. "It's time for all healthcare professionals to make sure that every pregnant and breast-feeding woman gets supplemental iodine during pregnancy and while they are breast-feeding."
"There is concern that even mild iodine deficiency in pregnant women could lead to children with lower IQ's," said Pearce. Iodine deficiency remains the leading cause of preventable mental retardation worldwide. Other risks of iodine deficiency include maternal and fetal goiter and increased pregnancy loss and infant mortality. Guidelines from the American Thyroid Association, Endocrine Society and Teratology Society have recommended daily iodine supplements for women in the U.S. who are pregnant, lactating or planning a pregnancy. However, these recommendations have not been widely adopted and many prenatal multivitamins sold do not contain iodine. [emphasis mine]
Are You Getting Enough Iodine in Your Diet?
Public health messages about not using the salt shaker have worked. In the United States, the salt shaker no longer accounts for the majority of sodium added to foods at the table. Unfortunately, sodium from iodized table salt has been replaced with sodium from non-iodized salt in processed foods. Too bad – we still have the problem of very high sodium intake yet now we have to consider the possibility of not getting enough iodine.[emphasis mine]