Maternal age‑stratified associations between Group B Streptococcus colonization and prenatal glucose metabolism and hemoglobin levels in pregnancy: a retrospective case‑control study

Abstract

Objective Group B Streptococcus (GBS) colonization during pregnancy is associated with adverse outcomes. The associations between GBS colonization status and clinical parameters measured at different antenatal time points, and whether these differ by maternal age, remain unclear. This study aimed to explore age-stratified associations between GBS colonization and clinical parameters.Methods A retrospective case-control study was conducted at a single center. Cases were GBS-positive women (n = 110), and controls were GBS-negative women (n = 155) selected from the same cohort and matched on key characteristics. Participants were stratified by maternal age (<35 [GBS-positive: n = 90; GBS-negative: n = 96] vs. ≥35 years [GBS-positive: n = 20; GBS-negative: n = 59]). GBS colonization was determined by standard culture of vaginal and perianal swabs at 35–37 weeks. Oral glucose tolerance test (OGTT) was performed at 24–28 weeks. Hemoglobin (Hb) levels and other biomarkers were compared between cases and controls within each age group.Results Among women aged < 35 years, GBS colonization was not associated with second-trimester OGTT results but was associated with lower third-trimester hemoglobin levels (116.98 ± 9.89 g/L vs. 120.49 ± 10.19 g/L in controls, p < 0.05) and a statistically significant but clinically negligible earlier gestational age at delivery (39.11 ± 1.05 vs. 39.41 ± 0.98 weeks, p = 0.04). In women aged ≥ 35 years, GBS colonization was associated with significantly higher fasting and 2-hour OGTT glucose levels (p < 0.05) and a higher second-trimester neutrophil percentage (76.27% ± 5.43% vs. 73.90% ± 4.08%, p = 0.04) compared to controls. The 1-hour OGTT value showed a non-significant trend (p = 0.06). No significant differences were observed in birth weight, infant sex, or mode of delivery.Conclusions This exploratory study suggests that maternal age may modify the associations between late-pregnancy GBS colonization status and clinical parameters measured earlier in gestation. The observed patterns highlight the potential importance of considering maternal age when evaluating prenatal laboratory findings in GBS-colonized women and generate hypotheses for future research. However, given the study’s retrospective design and the small sample size in subgroups, these findings should be interpreted with caution as hypothesis-generating rather than as evidence to guide clinical practice.