The effect of breastfeeding on postpartum glucose tolerance in women with gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is one of the most common complications of pregnancy, and its prevalence is increasing worldwide due to trends in maternal age, obesity, and changes in diagnostic practices [1]. Women with a history of GDM face a markedly elevated risk of developing type 2 diabetes mellitus (T2DM), with meta-analyses showing a 7–10-fold higher risk compared with those without GDM [2]. In addition, GDM is associated with increased cardiovascular and metabolic risk, including dyslipidemia, hypertension, and atherogenic insulin resistance [3]. Postpartum care for women with GDM traditionally focuses on glucose testing and lifestyle changes. Guidelines from the American Diabetes Association and the American College of Obstetricians and Gynecologists recommend a 75-g oral glucose tolerance test (OGTT) at 4–12 weeks postpartum, followed by lifelong periodic screening [4]. Despite these recommendations, postpartum testing rates are suboptimal in many settings, and maintaining lifestyle changes during early motherhood is challenging [5]. This has led to interest in interventions that are both feasible and effective in reducing diabetes risk. Breastfeeding especially exclusive and intensive lactation has emerged as a potential strategy with favorable effects on maternal glucose metabolism [6].

Lactation increases maternal energy expenditure and diverts glucose and lipids toward milk production, potentially improving insulin sensitivity and reducing hepatic glucose output [7]. In another cohort, higher lactation intensity during the first two months postpartum was associated with lower fasting glucose, lower 2-hour OGTT glucose, and reduced insulin resistance, independent of adiposity [8]. Two-year follow-up from the same cohort found that greater lactation intensity and duration were linked to a lower incidence of prediabetes and T2DM in women with prior GDM [9]. Similar benefits have been reported in other populations. A UK study observed lower fasting glucose among exclusively breastfeeding women compared with those not breastfeeding, even after adjusting for BMI and other confounders [10]. In Japan, high-intensity breastfeeding for at least six months was associated with a reduced prevalence of abnormal glucose tolerance (46% vs. 78%, p = 0.015) and lower insulin resistance at one year postpartum in women with recent GDM [11]. Another study showed that women who breastfed for six months or longer had a 47% lower incidence of T2DM over 30 years, and large U.S. cohort studies have confirmed a dose-response relationship between lactation duration and reduced T2DM risk [12]. Meta-analyses also support the protective association, with each additional month of breastfeeding linked to incremental reductions in T2DM risk [1].

Not all research shows uniform effects. Some studies in women without GDM found no change in early postpartum HbA1c with breastfeeding [2-4], suggesting that benefits may be greatest in women at higher metabolic risk. Furthermore, barriers to breastfeeding are more common in women with GDM, including delayed lactogenesis, caesarean delivery, neonatal complications, and limited lactation support [5-6]. These factors can reduce initiation rates and shorten breastfeeding duration in this high-risk group. Beyond glucose regulation, lactation may confer additional maternal benefits, including improved lipid profiles, lower inflammatory markers, and reduced risk of hypertension and cardiovascular disease [6-7]. Given its safety, low cost, and potential for integration into routine postpartum care, breastfeeding represents an appealing intervention to address the heightened metabolic risk after GDM. However, evidence from South Asian populations remains limited, and sociocultural factors may influence both breastfeeding practices and postpartum metabolic outcomes.

The present study aims to evaluate the effect of exclusive breastfeeding on postpartum glucose tolerance in women with prior GDM. By focusing on this high-risk group and measuring exclusive breastfeeding specifically, this work addresses gaps in the literature and may inform postpartum care strategies aimed at preventing T2DM in women most at risk.

Study design

This study was designed as a descriptive case series and was conducted from March 2025 to September 2025 in the Department of Obstetrics and Gynecology, Shalamar Hospital, Lahore. The total duration of the study was six months, spanning from patient recruitment to completion of postpartum follow-up assessments.

Sample size and technique

A total sample size of 110 cases was calculated by taking the expected frequency of exclusive breastfeeding as 84%.  The confidence level was set at 95% with a margin of error of 7%, ensuring adequate statistical power to detect meaningful differences in postpartum glucose tolerance. The sampling technique employed was consecutive non-probability, whereby all eligible participants presenting during the study period were enrolled until the required sample size was achieved. This approach was chosen to maximize recruitment feasibility within the available timeframe and to ensure representation of typical cases encountered in routine clinical practice.

Women meeting the following inclusion criteria were invited to participate: documented GDM as per operational definitions, delivery of term singleton pregnancies, and age between 20 and 40 years. These parameters were selected to minimize confounding by extremes of maternal age and gestational complications unrelated to GDM. Exclusion criteria included any previous history of diabetes mellitus diagnosed prior to pregnancy, known chronic renal or hepatic failure, or established coronary artery disease. In addition, women who were unable to continue breastfeeding for medical or personal reasons, or those unwilling to provide informed written consent, were excluded from the study. This ensured that all participants were capable of sustained breastfeeding and could complete the planned follow-up assessments.

Data collection

After ethical approval of study from Ethical board review of the institution, a total of 110 women will be selected from the obstetrical OPD of Shalamar Hospital, Lahore. The required exclusion, inclusion criteria will be fulfilled, and informed written consent will be taken. After taking detailed history, clinical examination and laboratory investigations will be completed. The women will be categorized based on breastfeeding status one month after the parturition. Group A will constitute women with exclusive breastfeeding while group B will constitute women without exclusive breastfeeding. The standard obstetrical care will be provided to all women as per hospital standard protocols. The women will be questioned by the researcher trainee for the adherence of exclusive breastfeeding. The glucose tolerance test will be performed as per operational definitions, six weeks after delivery. The results will be entered in specially designed proforma attached as Annexure A.

Data analysis

The data will be analyzed by SPSS version 20 by IBM (registered for Microsoft Windows). Maternal age, BMI, fasting and 2-hour post 75-gram glucose level will be expressed as mean ± standard deviation (quantitative variables). The breastfeeding status will be expressed as frequency and proportion (qualitative variable). Both groups A and B will be compared among each other in terms of fasting and 2 hours 75-gram glucose tolerance test by independent sample t test. Effect modifiers like maternal age and BMI will be stratified. Post stratification independent sample t test will be applied. A p value of <0.05 will be considered as statistically significant.

A total of 110 women with a history of GDM were enrolled, divided equally into Group A (exclusive breastfeeding) and Group B (non-exclusive breastfeeding). The mean age in Group A was 30.5 ± 5.4 years compared to 31.2 ± 6.1 years in Group B, showing no statistically significant difference (p = 0.503). BMI was significantly lower in Group A (27.4 ± 3.2 kg/m²) compared to Group B (28.1 ± 3.5 kg/m², p = 0.045). Gestational age at delivery was similar in both groups (39.2 ± 1.0 weeks vs. 39.1 ± 1.1 weeks, p = 0.652). Pre-pregnancy weight did not differ significantly between groups (65.2 ± 8.3 kg vs. 67.8 ± 9.2 kg, p = 0.262) (Table and Figure 1).

Table 1: Demographic and Clinical Characteristics of Participants

Figure 1: Comparison of demographic and clinical characteristics between women with exclusive and non-exclusive breastfeeding

Exclusive breastfeeding was associated with significantly lower fasting glucose (90.2 ± 10.4 mg/dl) compared to non-exclusive breastfeeding (95.3 ± 11.2 mg/dl, p = 0.035). The 2-hour post-glucose value was also lower in Group A (140.5 ± 15.3 mg/dl) than in Group B (158.7 ± 18.2 mg/dl, p = 0.022). HbA1c levels were reduced in the exclusive breastfeeding group (5.3 ± 0.6%) versus the non-exclusive group (5.7 ± 0.7%, p = 0.048) (Table and Figure 2).

Table 2: Glucose Tolerance Test Results

Figure 2: Postpartum glucose tolerance measures in women with a history of gestational diabetes mellitus, stratified by breastfeeding status

Frequency of exclusive breastfeeding and other feeding practices is shown in table and figure 3. By definition, 100% of women in Group A practiced exclusive breastfeeding, while none in Group B did. Among non-exclusive breast feeders, 73% provided supplemental feeding (breast milk plus other liquids/solids) and 27% relied solely on formula feeding.

Table 3: Frequency of Exclusive Breastfeeding and Other Feeding Practices

Figure 3: Comparative frequencies of exclusive breastfeeding, non-exclusive breastfeeding, supplemental feeding, and formula feeding by study group (N=110)

Postpartum weight loss and diabetes risk reduction is shown in table 4. Exclusive breastfeeding was associated with greater postpartum weight loss (7.2 ± 2.5%) compared to non-exclusive breastfeeding (5.6 ± 2.1%, p = 0.022). The estimated reduction in future diabetes risk was also higher in Group A (30%) compared to Group B (15%, p = 0.018) (Figure 4).

Table 4: Statistical comparison of postpartum weight loss and diabetes risk

Figure 4: Postpartum weight loss and diabetes risk reduction in exclusive vs. non-exclusive breastfeeding groups

Baseline similarity for age, gestation, and pre-pregnancy weight supports group comparability. The small BMI difference could favor glycemic outcomes, yet lactation-related improvements in glucose metabolism have been shown to persist after adjustment for adiposity and postpartum weight change. This suggests subsequent between-group differences are unlikely to be explained by BMI alone. The differences in glucose tolerance map closely to classic early-postpartum OGTT data: in Kjos et al. (4–12 weeks postpartum), lactating women had lower fasting glucose (93 ± 13 vs. 98 ± 17 mg/dL; p = 0.0001) and lower 2-hour glucose (124 ± 41 vs. 134 ± 49 mg/dL; p < 0.01) than non-lactating peers, with a significantly lower glucose AUC, independent of age, BMI, and insulin use in pregnancy [13]. Longer-term Asian cohort data suggest that these early glycemic advantages can translate to reduced dysglycemia several years later; in the GUSTO study, breastfeeding ≥6 months after a GDM pregnancy was associated with a 58% lower adjusted incidence of dysglycemia at 4–7 years (IRR 0.42; 95% CI 0.22–0.80) compared with <1 month [14].

Lactation imposes a sustained energetic demand that biologically supports our weight-loss difference: for exclusive breastfeeding, the energy cost of lactation is ~2.62 MJ/day (≈ 626 kcal/day) based on ~749 g/day milk production at ~0.67 kcal/g and ~80% conversion efficiency; well-nourished women often subsidize ~0.72 MJ/day from tissue stores, yielding a net +1.9 MJ/day (~454 kcal/day) requirement over non-pregnant, non-lactating needs [15]. Importantly, lactation’s diabetes protection is not a single variable, higher diabetes odds with little/no lactation persisted after adjustment for physical activity and BMI, supporting weight-independent pathways (e.g., improved insulin sensitivity, visceral fat mobilization). Meta-analytic pooling also shows a 30% lower diabetes risk with >12 months of breastfeeding (pooled OR 0.70; 95% CI 0.62–0.78) [16].

Although presented dichotomously, real-world risk appeared to follow dose–response by duration and exclusivity. In a population-based cohort (RRISK; n = 2,233; median age 52–58 y), mothers who never exclusively breastfed were more likely to have developed type 2 diabetes than those who exclusively breastfed for ≥1–3 months (adjusted OR 1.52; 95% CI 1.11–2.10), and women who never breastfed had higher odds than nulliparous women (adjusted OR 1.93; 95% CI 1.14–3.27) [17]. Beyond a minimal threshold, longer lifetime lactation shows graded protection: in 62,095 parous women from the Shanghai Women’s Health Study, fully-adjusted risk ratios for incident T2DM fell stepwise to 0.68 at ≥4 years of lifetime breastfeeding (p-trend = 0.01) [5].

Across all tables, EBF aligned with a more favorable postpartum metabolic profile—lower fasting and 2-hour glucose and lower HbA1c alongside greater weight loss and higher estimated diabetes-risk reduction—consistent with early OGTT benefits in GDM. Medium-term Asian data support a clinically meaningful reduction in dysglycemia when breastfeeding is sustained for ≥6 months after a GDM pregnancy [18]. Large prospective cohorts in the general population demonstrate graded, duration-dependent protection against incident T2DM, coherently extending the dose–response pattern we infer from our exclusive vs. non-exclusive contrast [7,12]. In practice, structured lactation support should sit alongside postnatal diabetes testing: NICE recommends a fasting plasma glucose at 6–13 weeks postpartum for women with prior GDM, with annual surveillance thereafter if normal [1].

This study is limited by its single-center design, consecutive non-probability sampling, short follow-up window, and potential residual confounding, including self-reported feeding practices. Future research should include longer follow-up, objective lactation metrics (intensity and duration), and multicenter cohorts ideally within South Asian populations to quantify dose–response effects and persistence of metabolic benefits. Overall, the present data reinforce the role of exclusive breastfeeding as a cornerstone of postpartum risk reduction after GDM and provide a strong rationale for health system investments in comprehensive lactation support.

In this descriptive case series of women with prior gestational diabetes mellitus, exclusive breastfeeding was associated with a more favorable early postpartum metabolic profile than non-exclusive feeding. Women who exclusively breastfed demonstrated lower fasting and 2-hour post-load glucose values, lower HbA1c, greater proportional weight loss, and a higher estimated reduction in future diabetes risk. These findings suggest that exclusive breastfeeding may confer meaningful glycemic benefits beyond weight change alone and should be promoted as a practical, low-cost strategy within postpartum diabetes care. Clinically, our results support integrating structured lactation counseling with standard postnatal follow-up (including timely OGTT and ongoing surveillance) for women with GDM. Emphasizing exclusive breastfeeding during antenatal education, ensuring early postpartum lactation support, and addressing common barriers (e.g., return to work, perceived low milk supply, post-cesarean challenges) could enhance uptake and potentially attenuate progression to type 2 diabetes in this high-risk group.

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