Objectives Over 1.9 billion people worldwide are living in areas estimated to be iodine insufficient. Strategies for iodine supplementation include campaigns targeting vulnerable groups, such as women in pre-conception, pregnancy and lactation. Portuguese women of childbearing age and pregnant women were shown to be mildly-to-moderately iodine deficient. As a response, in 2013, the National Health Authority (NHA) issued a recommendation that all women considering pregnancy, pregnant or breastfeeding, take a daily supplement of 150–200 μg iodine. This study explored how the iodine supplementation recommendation has been fulfilled among pregnant and lactating women in Portugal, and whether the reported iodine supplements intake impacted on adverse obstetric and neonatal outcomes. Design and methods Observational retrospective study on pregnant women who delivered or had a fetal loss in the Braga Hospital and had their pregnancies followed in Family Health Units. Results The use of iodine supplements increased from 25% before the recommendation to 81% after the recommendation. This was mostly due to an increase in the use of supplements containing iodine only. Iodine supplementation was protective for the number of adverse obstetric outcomes (odds ratio (OR) = 0.791, P = 0.018) and for neonatal morbidities (OR = 0.528, P = 0.024) after controlling for relevant confounding variables. Conclusion The recommendation seems to have succeeded in implementing iodine supplementation during pregnancy. National prospective studies are now needed to evaluate the impact of iodine supplementation on maternal thyroid homeostasis and offspring psychomotor development and on whether the time of the beginning of iodine supplementation (how early during preconception or pregnancy) is relevant to consider.