Maternal calcium supplementation and fetal bone mineralization

Objective: To determine the effect of maternal calcium supplementation duri ng pregnancy on fetal bone mineralization. Methods: Healthy mothers with early ultrasound confirmation of dates and si ngleton pregnancies were enrolled in a double-masked study and randomized b efore 22 weeks' gestation to 2 g/day of elemental calcium or placebo until delivery. Maternal dietary intake at randomization and at 32-33 weeks' gest ation was recorded with 24-hour dietary recalls. Dual-energy x-ray absorpti ometry measurements of the whole body and lumbar spine of the neonates were performed before hospital discharge. Results: The infants of 256 women (128 per group) had dual-energy x-ray abs orptiometry measurements during the first week of life. There were no signi ficant differences between treatment groups in gestational age, birth weigh t, or length of the infants, or in the total-body or lumbar spine bone mine ral content. However, when bone mineral content was analyzed by treatment g roup within quintiles of maternal dietary calcium intake, total body bone m ineral content (mean +/- standard error of the mean) was significantly grea ter in infants born to calcium-supplemented mothers (64.1 +/- 3.2 versus 55 .7 +/- 2.7 g in the placebo group) in the lowest quintile of dietary calciu m intake (less than 600 mg/day). The effect of calcium supplementation rema ined significant after adjustment for maternal age and maternal body mass i ndex and after normalization for skeletal area and body length of the infan t. Conclusion: Maternal calcium supplementation of up to 2 g/day during the se cond and third trimesters can increase fetal bone mineralization in women w ith low dietary calcium intake. However, calcium supplementation in pregnan t women with adequate dietary calcium intake is unlikely to result in major improvement in fetal bone mineralization. (Obstet Gynecol 1999;94:577-82. (C) 1999 by The American College of Obstetricians and Gynecologists.).