Vitamin D deficiency and pregnancy outcomes: LC-MS/MS-based evaluation in Southwest China

Vitamin D insufficiency is a global public health concern, particularly among Chinese pregnant women, yet southwest-China data using gold-standard LC-MS/MS are scarce.

A retrospective cohort study was conducted on 2,742 pregnancies delivered in Deyang. Serum 25(OH)D2 and 25(OH)D3 quantified by LC-MS/MS (CV < 7%). Univariate and multivariate logistic regression analyses were used to identify risk factors for vitamin D deficiency and assess its associations with pregnancy outcomes. Efficacy of vitamin D supplementation was also compared.

The median serum 25(OH)D concentration was 16.3 ng/ml, with 62.5% of participants classified as vitamin D deficient (<20 ng/ml). Early pregnancy (≤12 weeks) carried 3.37-fold higher deficiency risk than late pregnancy (≥25 weeks). Early deficiency was associated with gestational hypothyroidism (OR = 1.32, P = 0.048). Paradoxically, late deficiency inversely correlated with preterm birth (OR = 0.32, P = 0.014). One-month supplementation: D3-800 IU raised 25(OH)D by +28.4 ng/ml, outperforming D2-800 IU (+14.6 ng/ml, P < 0.001).

Vitamin D deficiency affects three-fifths of gravidae in Deyang. Early pregnancy represents the highest-risk window and predicts hypothyroidism. Late deficiency unexpectedly linked to lower preterm birth warrants causal clarification. D3 is the preferred supplement.