Amniotic fluid (AF), which is swallowed by the developing fetus, contains minerals and trace elements, but their association with fetal growth has not been explored. Our objectives were to assess (1) whether concentrations of AF minerals and trace elements were associated with changes in 5 fetal ultrasound measurements (estimated weight, bi-parietal diameter, head circumference, abdominal circumference, femur length) between 16-20 and 32-36 wks gestation and (2) whether a prenatal supplement was associated with concentrations of AF minerals and trace elements or the 5 fetal ultrasound measurements. We measured, using inductively coupled plasma-mass spectrometry (ICP-MS), 15 minerals and trace elements (aluminum, arsenic, calcium, chromium, copper, iron, lead, magnesium, nickel, potassium, rubidium, selenium, silver strontium, zinc) in amniotic fluid collected from 176 pregnant women undergoing age-related amniocentesis for genetic testing (15.7 +/- 1.1 wks). AF mineral concentrations, prenatal supplement use, and determinants of ultrasound measurements during early and late pregnancy were used in models to assess their impact on change in fetal ultrasound measurements. Positive associations were identified for change in bi-parietal diameter with AF calcium, for change in head circumference with AF copper and nickel, and for change in femur length with AF selenium. Arsenic was negatively associated with estimated fetal weight, and this relationship was modified by prenatal supplement use. Additionally, AF chromium concentrations were lower in women taking prenatal supplements. In conclusion, AF minerals were associated with fetal ultrasound indices, supporting a biological role for calcium, copper, nickel and selenium in promoting in-utero fetal growth. Evidence of a mineral-vitamin interaction between arsenic and folic acid in prenatal supplements and mineral-mineral interaction between iron and chromium would suggest that attention be paid to mineral and trace element formulation of prenatal supplements.
