Bone calcium turnover is aggravated in pregnant women recommended to bed rest. In the present cross-sectional study, we aimed to clarify whether preterm neonates would benefit from calcium supplementation during pregnancy. Forty-two mothers (37.5 ± 6.7 years), recommended bed rest at home, and 42 preterm neonates (24–37 weeks gestational age) were enrolled. Neonates’ serum calcium was quantified at birth. Mothers’ calcium intake from foods and supplements during pregnancy was assessed. Serum 25-OH-D was measured in both mothers and neonates at birth. Results showed that mothers’ calcium intake from foods was significantly lower than the recommended daily reference value (p < 0.001), while total calcium intake including supplements was close to the calcium reference value of 1000 mg/day (p = 0.648). Neonates’ serum calcium concentration was significantly higher in mothers receiving calcium supplementation during pregnancy compared to mothers who did not (p < 0.001). A significant association between neonates’ serum calcium levels and mothers’ calcium supplementation was evident, even when adjusted to mothers’ age, pre-pregnancy BMI, gestational age, and neonates’ birth weight (beta = +0.460, p = 0.025). A statistically significant correlation between neonates’ and mothers’ serum 25-OH-D levels was found (r = 0.891, p < 0.001). In conclusion, calcium status in preterm neonates, born by bedridden women, could be enhanced after calcium supplementation during gestation.