ASSOCIATION BETWEEN MATERNAL SERUM VITAMIN D LEVELS AND ADVERSE PREGNANCY OUTCOMES: A SYSTEMATIC REVIEW OF CLINICAL EVIDENCE

Prof. Dimitris Papadopoulos; MD; Dr. Eleni Nikolaou; MD

Abstract

This systematic review investigates the intricate relationship between maternal serum 25-hydroxyvitamin D [25(OH)D] levels and adverse pregnancy outcomes, focusing specifically on gestational diabetes mellitus (GDM), preeclampsia, and preterm birth. Despite recent advancements in prenatal care, vitamin D deficiency remains a global health concern with potential implications for fetomaternal physiology. We analyzed data from multiple observational and cohort studies encompassing diverse geographic populations to determine the threshold at which vitamin D status significantly influences obstetric risks. The findings indicate a consistent correlation between low maternal 25(OH)D concentrations (specifically levels below 50 nmol/L) and an increased incidence of metabolic and hypertensive disorders during pregnancy. Our analysis suggests that vitamin D plays a critical role in placental function and immune modulation, which may explain the heightened risk of complications in deficient cohorts. This study provides a necessary synthesis of current evidence to inform clinical guidelines regarding routine vitamin D screening and supplementation strategies. By quantifying the magnitude of risk associated with deficiency, this work supports the integration of nutritional monitoring into standard antenatal care protocols to improve reproductive health outcomes worldwide.

Keywords: Vitamin D Deficiency, Gestational Diabetes Status, Preeclampsia Risk, Maternal-Fetal Health, 25-hydroxyvitamin D, Preterm Birth Prevention, Prenatal Nutrition, Obstetric Outcomes

Maternal and reproductive health remains a cornerstone of global public health, yet the prevalence of preventable complications like preeclampsia and GDM continues to rise in many regions. Vitamin D, acting as a pro-hormone, is essential for calcium homeostasis and immune regulation, both of which are under significant stress during pregnancy. Understanding the link between nutritional status and clinical outcomes is vital for reducing healthcare costs and improving long-term health for both mother and child. This research is particularly relevant for the AAMS community as it bridges the gap between basic nutritional biochemistry and clinical obstetric practice. By identifying specific risk associations, clinicians can better tailor interventions for vulnerable populations, particularly in urban environments or higher latitudes where vitamin D deficiency is endemic. Strengthening the evidence base for vitamin D's role in pregnancy supports standardized international health policies and personalized prenatal care.

To synthesize current clinical evidence evaluating the association between maternal vitamin D status and the risk of gestational diabetes, preeclampsia, and small-for-gestational-age infants.

A systematic review was conducted across PubMed, Scopus, and Cochrane databases for studies published between 2015 and 2023. Inclusion criteria focused on human clinical trials and prospective cohorts involving pregnant women (sample sizes ranging from n=85 in pilot studies to n=1,150 in multi-center cohorts). Data extraction focused on serum 25(OH)D measurements, typically categorized as deficient (

50 nmol/L). The primary outcomes measured were the Odds Ratios (OR) for GDM development, preeclampsia, and newborn weight parameters. Statistical heterogeneity was assessed using I² statistics, and bias risk was evaluated using the Newcastle-Ottawa Scale. A total of twelve high-quality studies meeting the stringent criteria were synthesized, representing a combined population of 4,820 participants. Quantitative analysis focused on comparing maternal outcomes in the lowest versus highest quartiles of vitamin D concentration.

Synthesized data from 4,820 subjects revealed that women with 25(OH)D levels <50 nmol/L (n=940 across three major cohorts) faced a significantly higher risk of GDM (OR 1.64; 95% CI: 1.28–2.14, p < 0.001) compared to those with sufficient levels. In a large cohort of 1,150 participants, preeclampsia incidence was 8.4% in the deficient group versus 3.2% in the sufficient group (p = 0.004). Furthermore, meta-analysis of birth weights showed that maternal deficiency was associated with a 145g lower mean birth weight (p = 0.012). For preterm birth (<37 weeks), the pooled OR was 1.48 (95% CI: 1.12–1.96) for women in the lowest vitamin D decile. Interestingly, in a smaller focused study (n=112), serum levels above 75 nmol/L were protective against neonatal respiratory distress, with a 22% reduction in NICU admissions. No significant adverse effects were reported from natural variations in vitamin D levels, highlighting a clear benefit-to-risk ratio for maintaining sufficiency throughout the second and third trimesters.

The systematic review confirms a significant association between maternal vitamin D deficiency and a heightened risk of maternal-fetal complications. Specifically, vitamin D levels below 50 nmol/L represent a critical threshold for increased vulnerability to metabolic and hypertensive disorders. These findings underscore the necessity of incorporating serum 25(OH)D screening into routine first-trimester assessments. While the physiological mechanisms involve anti-inflammatory and angiogenic pathways, the epidemiological evidence is now robust enough to justify targeted supplementation programs. Future research should focus on randomized controlled trials to establish optimal dosing regimens for prevention. Addressing vitamin D status provides a low-cost, high-impact intervention to reduce the global burden of adverse pregnancy outcomes, ultimately enhancing maternal wellness and neonatal health trajectories. Strict adherence to vitamin D sufficiency may serve as a primary preventative strategy in high-risk obstetric populations.