Iron requirements increase significantly during pregnancy. Current recommendations for iron intake in pregnant and lactating women (PLW) are mainly based on factorial estimates and extrapolated from non-PLW. High-quality quantitative data on iron requirements in PLW are lacking, particularly in Sub- Saharan Africa where anaemia and infections are common.

The primary objective of this study is to use the stable iron isotope technique to determine iron requirements and assess iron absorption and losses in PLW living in Kenya.

In this prospective observational study, we will enrol pregnant women in the first trimester (n = 250) from a previous study cohort (n=1000) who participated in an iron absorption study at least 12 months ago and received the stable iron (Fe) isotope 57Fe. This 57Fe has now distributed and equilibrated throughout the women's body iron. Once enrolled in the present study, following Kenyan guidelines, women will receive standard prenatal care, including routine daily iron and folate supplementation. We will collect venous blood samples in each trimester and at delivery, and during the first 6 months of lactation in the mothers and infants (heel prick samples). To directly assess dietary iron absorption, in a randomly selected subset of women (n=35), oral and intravenous stable iron isotope tracers (54Fe, 58Fe) will be administered in the 2nd and 3rd trimesters.

Inclusion Criteria:

• Providing consent to the informed consent form
• Participation in a previous stable isotope absorption study and having received an oral dose of 15 mg 57Fe at least 12 months prior to the date of inclusion in the study
• Positive pregnancy test and gestational age <10 weeks based on history of last menstrual period
• Permanent residence in the study area, and not expected to leave the study site for more than 4 weeks over the following 16 months
• Assessment of good health by professional staff at Msambweni Hospital

Exclusion Criteria:

• Pre-pregnancy body mass index >30 kg/m2
• Blood transfusion or intravenous iron treatment within 4 months of study start
• Major chronic infectious disease (e.g., tuberculosis, HIV+, hepatitis)
• Major chronic non-infectious disease (e.g., Type 1 or 2 diabetes, cancer)

This study will recruit 250 pregnant women in the first trimester who previously participated in a stable iron isotope study (Clinical Trial ID: NCT05266703) and received 15 mg of the stable iron isotope 57Fe as an oral dose of ferrous sulphate at least 12 months before being enrolled in this trial.