Second-Trimester Blood Minerals May Signal Gestational Diabetes Risk, Study Finds

A routine blood test taken in mid-pregnancy may reveal more than clinicians currently expect. A retrospective cohort study of 700 pregnant women treated at the Fourth Hospital of Shijiazhuang in Hebei Province, China, has linked second-trimester serum levels of three common minerals—magnesium, phosphorus, and calcium—to the risk of gestational diabetes mellitus (GDM) and to other adverse pregnancy outcomes, including anemia and preterm birth. The findings, published in Frontiers in Clinical Diabetes and Healthcare, suggest that the mineral profile of a pregnant woman’s blood could one day serve as an accessible early-warning signal for one of the most common complications of pregnancy.

Gestational diabetes mellitus is a form of glucose intolerance that first appears during pregnancy and typically resolves after delivery, but its consequences can be far from temporary. Poorly controlled maternal blood sugar raises the risk of macrosomia, in which the baby is born excessively large, and increases the likelihood of birth injuries, cesarean delivery, and neonatal metabolic problems. Over the longer term, women who develop GDM face elevated lifetime risks of type 2 diabetes and cardiovascular disease, while their children carry a higher susceptibility to obesity and metabolic dysfunction. Because the condition is so prevalent, researchers have long sought modifiable risk factors that could be identified and corrected before the disease takes hold.

Known susceptibility factors include maternal age, pre-pregnancy body mass index, and a family history of diabetes, but the role of mineral metabolism has received comparatively little systematic attention. The research team, led by Achou Su, Jie Zhang, and colleagues at the Fourth Hospital of Shijiazhuang, focused on three minerals with well-established biochemical roles in glucose handling. Magnesium acts as a cofactor in enzymes of energy metabolism and protein synthesis and has been shown in previous trials to improve insulin sensitivity when supplemented. Calcium participates in insulin signaling within pancreatic beta cells and in calcium-dependent transport proteins whose disruption has been observed in GDM. Phosphorus, by contrast, has a more ambiguous metabolic reputation: dietary phosphorus intake has been linked in a U-shaped pattern to new-onset diabetes in the general Chinese population, yet its relationship to GDM had remained unreported.

The study population consisted of 700 women aged 18 to 45 who received antenatal care and delivered at the hospital between January 2022 and December 2023. All participants carried singleton pregnancies and had no pre-existing metabolic diseases, thyroid disorders, liver or kidney disease, immune conditions, or polycystic ovary syndrome. Women with a history of abnormal glucose tolerance or diabetes before pregnancy were excluded, as were those with abortion or bleeding during delivery. Blood samples were drawn in the morning after at least eight hours of fasting, at 24 to 28 weeks of gestation, and analyzed on a Roche Cobas 701 automated biochemical analyzer using manufacturer-specific calibrators. Crucially, the mineral measurements and the oral glucose tolerance test used to screen for GDM were performed at the same visit, before any dietary adjustment or hypoglycemic therapy had begun.

The diagnostic framework followed international and national standards. GDM was diagnosed when at least one of three glucose thresholds was met during the oral glucose tolerance test: a fasting plasma glucose between 5.1 and 6.9 mmol/L, a one-hour value of 10 mmol/L or higher, or a two-hour value between 8.5 and 11 mmol/L. Anemia was graded by hemoglobin concentration, with mild anemia defined as 100 to below 110 g/L, moderate as 70 to below 100 g/L, and severe as below 70 g/L. Preterm birth was defined as delivery before 37 weeks of gestation. Additional outcomes, including premature rupture of membranes, chorioamnionitis, preeclampsia, macrosomia, low birth weight, and neonatal respiratory distress syndrome, were classified according to ACOG and WHO criteria.

Of the 700 women, 571 experienced at least one adverse pregnancy outcome, while 129 had no gestational complications or abnormal delivery outcomes. Baseline characteristics—including age, pre-pregnancy BMI, education, household income, parity, family history of diabetes, and prior adverse pregnancy history—were statistically indistinguishable between the two groups, which strengthened the case that any differences in mineral levels were not simply reflections of demographic imbalance. When the researchers compared serum mineral concentrations between women who developed GDM and those who did not, all three minerals showed significant differences, with the GDM group exhibiting lower magnesium and calcium and higher phosphorus.

To quantify these associations, the team converted mineral values into increments of 0.1 mmol/L and applied multivariable logistic regression, adjusting for age, preconceptional BMI, family history of diabetes, adverse pregnancy history, and parity. Each 0.1 mmol/L increase in serum magnesium was associated with an 28 percent reduction in GDM odds (adjusted odds ratio 0.718, 95% CI 0.576–0.896, p = 0.003), while the same increment in calcium was linked to a 52 percent reduction (OR 0.484, 95% CI 0.400–0.585, p < 0.001). Phosphorus moved in the opposite direction: each 0.1 mmol/L rise in serum phosphorus increased the odds of GDM by roughly 15 percent (OR 1.145, 95% CI 1.016–1.290, p = 0.027). Calcium also showed a protective association with anemia (OR 0.729, 95% CI 0.618–0.860, p < 0.001) and with preterm birth (OR 0.687, 95% CI 0.501–0.927, p = 0.014), whereas phosphorus was positively associated with preterm birth risk (OR 1.403, 95% CI 1.118–1.762, p = 0.004).

Receiver operating characteristic (ROC) analysis added a predictive dimension to the findings. Among the three minerals individually, calcium showed the strongest discriminative ability for GDM, with an area under the curve (AUC) of 0.684 (95% CI 0.639–0.730, p < 0.001); at a cut-off of 2.025 mmol/L it achieved a sensitivity of 65.4 percent and a specificity of 68.9 percent. Magnesium yielded an AUC of 0.588, with a cut-off of 0.725 mmol/L giving 64.9 percent sensitivity and 52.9 percent specificity, while phosphorus was the weakest single predictor at an AUC of 0.559. When the three minerals were combined into a single logistic regression model, the AUC rose to 0.733 (95% CI 0.691–0.775, p < 0.001), with an optimal probability cut-off of 0.301 delivering 66.8 percent sensitivity and 72.9 percent specificity. The combined model, the authors note, provides superior clinical risk stratification compared with any single mineral measurement.

The biological mechanisms underlying these associations are plausible but not yet proven. Magnesium and calcium are thought to reduce insulin resistance and promote insulin sensitivity, thereby supporting stable glycemic control. Prior research has shown that magnesium supplementation during pregnancy can lower fasting blood glucose in women with GDM and upregulate the gene expression of glucose transporter 1, improving glucose and lipid metabolism. Combined calcium and vitamin D supplementation has likewise been shown to reduce fasting glucose and serum insulin in GDM patients. On the other side of the ledger, elevated phosphate may disrupt glucose homeostasis through the FGF-23/Klotho signaling pathway, a hormonal axis that regulates phosphate and vitamin D balance, and excess phosphorus has been shown to promote reactive oxygen species production, driving pancreatic beta-cell apoptosis and reduced insulin secretion. High phosphorus may also activate the NLRP3 inflammasome, a molecular complex implicated in the initiation of labor, which could explain the observed link to preterm birth.

The authors are careful to frame their conclusions as observational correlations rather than causal claims. The retrospective design carries inherent limitations: standardized records of antenatal mineral, vitamin D, and combined nutritional supplements were not systematically archived, potentially introducing confounding bias; only total serum calcium was measured without albumin correction, so physiological gestational hypoalbuminemia may have lowered total calcium readings independent of biologically active ionized calcium; mineral levels were tested only once, at 24 to 28 weeks, and therefore cannot capture the dynamic changes of mineral metabolism across the full course of pregnancy; and, as an observational study, the work cannot establish definitive causal relationships, although the simultaneous timing of blood collection and GDM screening reduced the risk of reverse causation. The team explicitly states that randomized controlled trials are essential before any supplementation recommendations can be drawn, and that larger prospective studies are needed to verify the findings. Still, the results point toward a practical possibility: that a modest panel of mineral measurements, already part of routine prenatal bloodwork in many settings, could help clinicians identify women at elevated risk of gestational diabetes earlier in pregnancy and tailor nutritional guidance accordingly.

Subject of Research: Association of second-trimester serum magnesium, phosphorus, and calcium levels with gestational diabetes mellitus and adverse pregnancy outcomes

Article Title: The correlation between serum magnesium, phosphorus, and calcium levels during pregnancy and the risk of gestational diabetes mellitus as well as adverse pregnancy outcomes

Article References: Su, A., Zhang, J., Fan, X., Song, W., Li, M., Yu, T., & Zhang, J. (2026). The correlation between serum magnesium, phosphorus, and calcium levels during pregnancy and the risk of gestational diabetes mellitus as well as adverse pregnancy outcomes. Frontiers in Clinical Diabetes and Healthcare, 7, Article 1939424. https://doi.org/10.3389/fcdhc.2026.1939424

Image Credits: AI Generated

DOI: 10.3389/fcdhc.2026.1939424

Keywords: gestational diabetes mellitus, magnesium, phosphorus, calcium, pregnancy outcomes, preterm birth, anemia, mineral metabolism, insulin resistance, retrospective cohort study, maternal nutrition, ROC analysis