Iodine is essential for intellectual development. Its deficiency, alone, is the most frequent cause of preventable brain harm in infants. Iodine is required to synthesize thyroid hormones, key components of central nervous system development. Because of its relevance in pregnancy, several countries have implemented iodine supplementation programs in preconception, pregnancy and lactation.

Iodine deficiency has been previously shown in women of childbearing age in Portugal. Because of this, since 2013 the National Health Authorities have recommended supplementing iodine (200 ug/day) in preconception, pregnant and lactating women. However, the latest Cochrane review on the subject does not allow to conclude on whether iodine supplementation strategies implemented to date are efficient. Therefore, this study is of great public health interest.

The objectives are to:

• Evaluate whether the new policy of recommending iodine supplementation in preconception, throughout pregnancy and during lactation impacted on the prevalence of iodine deficiency in the Minho region of Portugal when compared to the same population before the recommendation.
• Evaluate whether the time of initiation of iodine supplementation (if any) influences the serum levels of thyroid hormones in the three trimesters of pregnancy.
• Evaluate whether the serum levels of thyroid hormones in the first trimester of pregnancy predict psychomotor development of the newborn at 12 months of age.

To achieve these aims the investigators will follow: i) 1000 women longitudinally, before, during the three trimesters of pregnancy (primary care Health Centres), at delivery and three months after delivery, ii) their children at birth, 3 and 12 months of age; ii) perform a detailed evaluation of parameters of thyroid function (mother and child) and of psychomotor development of the newborns.

Investigators expect to provide detailed characterization of thyroid hormone homeostasis before and throughout pregnancy, their relation with iodine supplementation (and its timing of administration, if any) and with thyroid hormone parameters and psychomotor development of the newborn.

With 6 years passed since the beginning of recommendation on iodine supplementation, this is an appropriate time to assess its effectiveness. The high number of samples and parameters to analyze make this a high-power study to support public health policies.