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Control of vitamin D metabolism in preterm infants: feto-maternal relationships
Insights
Maternal and fetal mineral homeostasis shows significant transfer of calcium, magnesium, and phosphate against gradients. The fetus relies on maternal vitamin D supply, while synthesizing 1,25-dihydroxyvitamin D based on fetal needs after 31 weeks gestation.
Area of Science:
- Obstetrics and Gynecology
- Neonatology
- Endocrinology
Background:
- Maternal and fetal mineral and vitamin D metabolite homeostasis are crucial for pregnancy outcomes.
- Understanding placental transfer mechanisms and fetal-placental unit synthesis is vital.
Purpose of the Study:
- To assess the relationship between maternal and fetal mineral and vitamin D metabolite concentrations.
- To investigate placental transfer of calcium, magnesium, inorganic phosphate, and vitamin D metabolites.
- To examine fetal synthesis of vitamin D metabolites.
Main Methods:
- Comparison of serum concentrations of calcium, magnesium, inorganic phosphate, parathyroid hormone, and vitamin D metabolites in maternal and cord sera.
- Analysis included samples from 15 preterm singletons and 3 twin pairs.
Main Results:
- Cord serum calcium, magnesium, and inorganic phosphate were significantly higher than maternal levels, indicating transfer against a concentration gradient.
- Cord serum 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D were lower than maternal levels, suggesting fetal dependence on maternal supply.
- Cord 1,25-dihydroxyvitamin D correlated with cord calcium, suggesting fetal synthesis based on fetal needs.
Conclusions:
- Calcium, magnesium, and inorganic phosphate cross the placenta against a concentration gradient after 31 weeks gestation.
- The fetus depends on maternal supply for 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D.
- The feto-placental unit synthesizes 1,25-dihydroxyvitamin D according to fetal requirements.
Abstract:
To assess the relationship between maternal and fetal mineral homeostasis, serum calcium, magnesium, inorganic phosphate, parathyroid hormone, and vitamin D metabolite concentrations in venous cord sera from 15 preterm singletons and 3 twin pairs were compared with the levels found in maternal sera. Cord calcium, magnesium, and phosphorus levels were significantly higher than the respective levels in maternal samples. There was a significant relationship between the two compartments for all three analyses. Cord serum 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, and 1,25-dihydroxyvitamin D levels were significantly lower than those observed for the mothers. Association of the cord concentration with that of the mothers was observed only for the first two metabolites. There was no relationship between the maternal 1,25-dihydroxyvitamin D levels and gestational age, calcium, magnesium, inorganic phosphate, or 25-hydroxyvitamin D. Cord 1,25-dihydroxyvitamin D correlated significantly only with cord calcium levels. Immunoreactive parathyroid hormone levels were within normal limits both in cord and maternal samples. Our data suggest that after 31 weeks of gestation: (1) calcium, magnesium, and inorganic phosphate cross the placental barrier against a concentration gradient; (2) the fetus depends on the maternal supply for 25-hydroxyvitamin D and 24,25 dihydroxyvitamin D; (3) the feto-placental unit synthesizes 1,25-dihydroxyvitamin D according to fetal needs.