First-trimester hemoglobin, haptoglobin genotype, and risk of gestational diabetes mellitus in a retrospective study among Chinese pregnant women.

Background: This study aimed to assess whether the Haptoglobin (Hp) genotype influences the relationship between hemoglobin (Hb) levels and the development of gestational diabetes mellitus (GDM). Additionally, it sought to evaluate the interaction and joint association of Hb levels and Hp genotype with GDM risk.

Methods: This retrospective study involved 358 women with GDM and 1324 women with normal glucose tolerance (NGT). Peripheral blood leukocytes were collected from 360 individuals at 14-16 weeks' gestation for Hp genotyping. GDM was diagnosed between 24-28 weeks' gestation. Interactive moderating effect, joint analysis, and mediation analysis were performed to evaluate the crosslink of Hb levels and Hp genotype with GDM risk.

Results: Women who developed GDM had significantly higher Hb levels throughout pregnancy compared to those with NGT. Increase first-trimester Hb concentration was associated with a progressive rise in GDM incidence, glucose levels, glycosylated hemoglobin levels, Homeostasis Model Assessment for Insulin Resistance (HOMA-IR) values, cesarean delivery rates, and composite neonatal outcomes. Spline regression showed a significant linear association of GDM incidence with continuous first-trimester Hb level when the latter exceeded 122 g/L. Increased first-trimester Hb concentration was an independent risk factor for GDM development after adjusting for potential confounding factors in both the overall population and a matched case-control group. The Hp2-2 genotype was more prevalent among pregnant women with GDM when first-trimester Hb exceeded 122 g/L. Significant multiplicative and additive interactions were identified between Hb levels and Hp genotype for GDM risk, adjusted for age and pre-pregnancy BMI. The odds ratio (OR) for GDM development increased incrementally when stratified by Hb levels and Hp genotype. Moreover, first-trimester Hb level partially mediated the association between Hp genotype and GDM risk.

Conclusion: Increased first-trimester Hb levels were closely associated with the development of GDM and adverse pregnancy outcomes, with this association moderated by the Hp2-2 genotype.