The goal of this clinical trial is to learn about the effects of iodine-containing multiple micronutrient supplements provided to breastfeeding mothers who live in settings with mild iodine deficiency.

The main questions it aims to answer are:

1. What are the effects of iodine-containing multiple micronutrient supplements provided to breastfeeding mothers on infant development, as measured by electroencephalography/visual evoked potentials?
2. What are the effects of iodine-containing multiple micronutrient supplements on breast milk concentrations of iodine, and infant iodine and thyroid status?
3. How do iodine and iron interact with each other to affect thyroid function in the mother during lactation?

Participants will be randomized to receive a daily multiple micronutrient tablet containing iodine (UNIMAPP) for 6 months postpartum, or routine postnatal care per Ethiopia Ministry of Health. Mothers will provide a breast milk sample and blood at 3 and 6 months postpartum. Infants will provide a urine sample and drop of blood, and have a neurodevelopmental assessment at 3 and 6 months.

Researchers will compare the groups that received the iodine-containing micronutrient supplement with the group that received routine care and see if there were any benefits on infant development and iodine and thyroid status in the mother and baby.

To be eligible, women will be required to meet the following inclusion criteria:

• Maternal age 18 years or above, singleton pregnancy,
• data available on Last Menstrual Period (LMP) or early ultrasound,
• Intention to exclusively feed breastmilk for 4 to 6 months,
• Intention to stay in the study catchment area for at least 6 months,
• Willingness to take a daily supplement of MMS for 6 months

Exclusion criteria include:

• Severe maternal morbidity (postpartum eclampsia, postpartum hemorrhage),
• Maternal condition leading to inability for infant to directly/exclusively breastfeed (maternal mastectomy, or other breast surgery),
• Breast cancer,
• Tuberculosis