Effect of parity on the serum calcium in the pregnancy: A retrospective study

Background: Maternal hypocalcaemia has adverse outcomes on pregnant women and offspring development. The objective of this study is to test whether parity number is associated with maternal calcium level. Materials and Methods: According to parity numbers, the pregnant women were divided into never parturition group (NPG) and previous parturition group (PPG). Association between parity number and serum calcium was tested in multivariate linear regression models controlling for age, body mass index (BMI), Vitamin D, and Homeostasis model assessment for insulin resistance (HOMA-IR). The subjects were also subgrouped by recruitment in four seasons and their development of gestational hypertension (GH) and diabetes. Results: Mean serum calcium was lower in the PPG than that in the NPG (2.15 vs. 2.20 mmol/L, P < 0.001). After adjusted for albumin, adjusted serum calcium was still lower in PPG than that in NPG (2.20 vs. 2.23 mmol/L, P < 0.001). Interestingly, adjusted serum calcium level is consistently lower in the PPG in both the diabetic and hypertension subgroups compared to NPG (2.20 vs. 2.23 mmol/L, P < 0.001). In different seasons, the serum calcium level and adjusted serum calcium level in the PPG were significantly lower than the NPG (P < 0.001). Importantly, adjusted calcium correlated negatively with the parity number (r = −0.044, P < 0.001), when adjusting for age, BMI, Vitamin D, and HOMA-IR. In addition, there was a significant increase in the PPG compared to the NPG including age (29.61 vs. 33.39 years old), BMI (22.80 vs. 23.55), triglyceride (2.27 vs. 2.43 mmol/L), and fasting basal blood glucose (4.73 vs. 4.81 mmol/L), and a significant decrease regarding the albumin (38.72 vs. 37.65 g/L) and Vitamin D (20.98 vs. 18.62 ng/ml). There was no difference in the onset of GH and gestational diabetes mellitus (GDM) between the two groups. Conclusion: Parity negatively correlated with the serum calcium level. The small but significant difference in the calcium levels indicated that parity may play an intricate role in calcium homeostasis. Timely monitoring of maternal calcium could be clinically beneficial to the multiparous women.