Maternal calcium metabolic stress and fetal growth

INTRODUCTION:  It was hypothesized that it was maternal calcium metabolic stress in early pregnancy, rather than sub-optimal calcium intake or insufficient vitamin D that influenced risk of small for gestation births (SGA), and other aspects of fetal growth. Stress to calcium metabolism was defined by elevated intact PTH (>62 pg/ml) accompanied by very low calcium intake (<60% EAR) or insufficient 25 (OH) D (<20 ng/ml).

METHODS:  A prospective cohort study of 1116 low income and minority gravidae at entry to care 13.8 ± 5.6 weeks (mean ± SD) from Camden NJ. 

RESULTS:  The concentration of PTH depended upon circulating 25 (OH) and total calcium intake.  When 25 (OH) D was insufficient even a high calcium intake which equaled or exceeded the RDA was unable to maintain PTH or to moderate the proportion with elevated PTH.  When examined one at a time, very low calcium intake (<60% EAR), very low 25 (OH) D (<12 ng/ml) and elevated PTH (>62 pg/ml) each had a small but significant association with birth weight (~100 g lower). Elevated PTH was also related to birth length and risk of SGA. Elevated PTH accompanied by insufficient 25(OH)D or very low calcium intake showed two to three-fold increased risks of SGA (15.1% vs 7.8%, AOR= 2.23, 95% CI 1.12, 4.43 all women) as well as for those without preeclampsia (17.4% vs 7.1%, AOR=3.26 95% CI 1.58, 6.73) and significantly lower birth weight(-128.5 ± 49.9g), birth length(-0.63±0.28cm) and head circumference( -0.42±0.21cm ) even  after excluding women who developed preeclampsia. Infants born to gravidae with insufficient 25(OH) D or very low calcium intake without elevated PTH or with elevated PTH alone were unaffected.

CONCLUSIONS:  Maternal calcium metabolic stress, rather than low calcium intake or insufficient vitamin D, has an adverse influence on fetal growth.