Glycemic Patterns and Breastfeeding With Type 1 or Type 2 Diabetes

Abstract

Breastfeeding presents distinct physiological and practical challenges in individuals with type 1 or type 2 diabetes. This review examines the barriers to successful lactation in this population, evaluates evidence-based interventions to address these obstacles, provides clinical recommendations regarding medication and nutritional management, and delineates the impact of diabetes on lactation physiology.

Breastfeeding is universally recommended for its numerous health benefits to both mothers and infants. For women with diabetes, however, the postpartum period presents unique physiological and clinical challenges, particularly related to glycemic control and insulin dosing. Understanding glycemic patterns during lactation is essential to support safe and successful breastfeeding among women with diabetes.

Although initiation and continuation of lactation is more challenging with pregestational diabetes (i.e., diabetes present before pregnancy), it comes with significant physical and emotional rewards. Counseling and careful management is required to ensure successful breastfeeding and maintain glycemic goals.

Recent studies using continuous glucose monitoring (CGM) and insulin pump technology have provided valuable insights into the relationship between lactation and maternal glycemic patterns. This review explores these findings, with a focus on glucose dynamics during breastfeeding, insulin management, barriers to breastfeeding, medication safety, and future research directions for individuals with type 1 or type 2 diabetes.

Benefits of Breastfeeding

Breastfeeding is beneficial for both mothers and infants, leading to global recommendations for exclusive breastfeeding for up to the first 6 months, followed by continued breastfeeding with the addition of complementary foods for 2 years or longer (1). There are many benefits to breastfeeding. Childhood obesity is reduced in those who breastfeed, independent of maternal BMI and diabetes type (2). Breast milk contains immunoglobulins that reduce the risk of acquiring childhood infections. Importantly, breastfeeding minimizes neonatal hypoglycemia (3). The act of feeding bonds the mother-infant dyad with a positive impact on infant neurodevelopment, heightened cognitive performance, reduced markers of physiological stress, and secure attachment. Mothers benefit emotionally and demonstrate objective evidence of stress reduction, with higher-quality sleep patterns, increased cardiac vagal tone, and reduced blood pressure and heart rate (4). Breastfeeding increases energy consumption by an average of 450 kcal/day in the first 6 months postpartum (5). Because of the high calorie demands of breastfeeding, there is increased maternal weight loss with higher likelihood to return to pre-pregnancy weight. Mothers who breastfeed also have a reduced risk of cardiovascular disease (6).

Barriers to Breastfeeding in Women With Diabetes

Despite the benefits of breastfeeding, women with diabetes are less likely to initiate or maintain breastfeeding compared with their peers without diabetes (7–9). Several physiological and systemic barriers that contribute to this discrepancy include the following.

• Delayed lactogenesis. Diabetes is associated with a delayed onset of copious milk production (i.e., lactogenesis II), especially in cases of poor glycemic control (10).

• Operative deliveries and neonatal intensive care unit (NICU) admissions. Increased rates of cesarean section and neonatal complications result in delayed mother-infant bonding and breastfeeding initiation (7,11).

• Fear of hypoglycemia. This remains a significant deterrent to breastfeeding initiation and continuation, particularly among insulin-treated individuals (8). Despite these barriers, research shows that fear of hypoglycemia is often disproportionate to actual risk, particularly when insulin doses are appropriately reduced postpartum. Use of CGM is also beneficial in reducing the risk of hypoglycemia through frequent assessment of glycemic levels and trends, which can show whether glucose is rising, stable, or falling. In a blinded CGM study (12), postpartum mothers who breastfed were compared with age- and BMI-matched control subjects who bottle-fed their infants. Nighttime hypoglycemia with CGM was low (4.6% in the first month, 3.1% in the second month, and 2.7% in the sixth month) in those who breastfed. These rates of hypoglycemia were lower than those who formula-fed, although differences did not reach statistical significance. Breastfeeding mothers spent more time at goal and had less hyperglycemia compared to those who bottle-fed.

• Breast milk volume. Both hypoglycemia and hyperglycemia lead to lower breast milk volume, with decreases if up to 50% particularly seen with hypoglycemia (13). Breastfeeding duration is shorter in people with type 1 diabetes or type 2 diabetes compared with the general population, although 90% of breastfeeding cessation the result of perceived poor milk supply (11).

Exclusive breastfeeding after hospital discharge occurs less often in those treated with insulin. Differences have not been identified based on delivery mode or whether infants require NICU admission (9). However, other studies have demonstrated that mother-infant separation is a barrier to breastfeeding in cohorts with and without diabetes. Strategies that promote breastfeeding even when the newborn is in the NICU include rooming-in suites, which are available in some hospitals, accommodating visitation hours in the NICU, access to private feeding and pumping rooms, and access to lactation counselors.

Glycemic Patterns During Breastfeeding

Glycemic Response to Suckling

In individuals without diabetes, infant suckling does not affect maternal glucose levels; however, the same is not true in individuals with type 1 diabetes. Oxytocin, a hormone released during lactation, mediates the milk ejection reflex. Oxytocin receptors are also expressed in insulin-sensitive tissues, including adipocytes and skeletal and cardiac muscle. Infant suckling stimulates maternal release of oxytocin from the pituitary gland and may play a key role in glycemia by enhancing glucose uptake into skeletal and cardiac muscle, thereby contributing to the observed decrease in glucose levels during or after breastfeeding episodes. However, oxytocin also stimulates glucagon secretion, which raises blood glucose levels (14,15). In people with type 1 diabetes, there is progressive loss of glucagon secretion over time, which may make oxytocin’s role in enhanced glucose uptake more pronounced, causing more hypoglycemia.

Prolactin is another pituitary hormone important in lactation and necessary for milk secretion from mammary alveoli. Prolactin also acts directly on pancreatic β-cells, increasing insulin release in people who do not have type 1 diabetes. Prolactin suppresses lipogenesis in adipose tissue and decreases GLUT4 receptor expression, which reduces glucose uptake. These actions have conflicting effects that simultaneously cause increased insulin release and insulin resistance (16).

Postpartum Glycemic Trends

Multiple studies suggest that, although breastfeeding can modestly reduce maternal blood glucose levels, the risk of significant hypoglycemia is generally low, particularly with appropriate insulin dose adjustments.

GLUT1 is the critical glucose transporter and plays a key role in passive transport of glucose to the mammary glands. Once in the mammary cells, the glucose is used to synthesize lactose. In individuals without diabetes, the free glucose concentration in breast milk is constant regardless of breast store time. In those with type 1 diabetes, breast milk has a higher and more variable free glucose content, although the absolute difference is low, and lactose content is comparable.

In a secondary analysis of the CLIMB (Closed-Loop Insulin in Mothers With Type 1 Diabetes and Baby Feeding Practices) randomized controlled trial (RCT), Donovan et al. (17) used CGM to assess glucose levels within 3 hours of breastfeeding in postpartum women using a hybrid closed-loop automated insulin delivery (AID) system. Among 18 participants, 93% of breastfeeding episodes did not result in glucose values dropping to <70 mg/dL, and only two of 12 women experienced hypoglycemia in the immediate post-feed period (17). Nighttime episodes showed a slightly higher risk, with low glucose events recorded during 2.9% of feeds with an AID system and 8.8% of those with open-loop therapy. Nighttime blood glucose levels were 14 mg/dL lower on average in those with open-loop insulin pump systems compared with those managed with a closed-loop AID system in the first 12 weeks postpartum. Daytime feeds, by contrast, were not associated with significant mean glucose decreases. These results underscore the relative safety of AID during lactation but highlight the need for vigilance during nocturnal feeds.

Ringholm et al. (12) conducted a blinded CGM study over the first 6 months postpartum in 33 women with type 1 diabetes. At 1, 2, and 6 months, average insulin doses were 18, 14, and 14% lower than pre-pregnancy levels, respectively. Nighttime hypoglycemia was uncommon (4.6% in month 1, 3.1% in month 2, and 2.7% in month 6), and breastfeeding mothers had better time-in-range CGM metrics and less hyperglycemia than matched control subjects.

Although lactation-associated hypoglycemia is rare overall, more hypoglycemic episodes occur at night. Daytime breastfeeding has not been demonstrated to result in significant reductions in glucose (17). Monitoring via CGM versus intermittent checks with a blood glucose meter will reflect more accurate trends and better enable identification of glycemic patterns.

Postpartum Insulin Management

Postpartum insulin requirements typically decline as a result of decreased insulin resistance after placental delivery. Several studies have recommended reducing insulin doses to 60–70% of pre-pregnancy levels in the early postpartum period (18,19). A1C is not a reliable indicator of glycemic control postpartum because there is a physiological decrease in A1C with advancing gestation and, additionally, blood loss during delivery can cause falsely low A1C values (20).

In a study by Nørgaard et al. (21), women using insulin pumps maintained stable glycemic control across 6 months postpartum with insulin basal rates ∼14% lower than in the pre-pregnancy period and insulin-to-carbohydrate ratios 10% higher. AID systems, particularly those with features that will suspend insulin delivery ahead of predicted low blood glucose levels, have proven effective in reducing nocturnal hypoglycemia during lactation (17).

Other studies confirm minimal risk of severe hypoglycemia and suggest that proper carbohydrate intake, carbohydrate counting, and the use of predictive low-glucose suspend features on insulin pumps can mitigate risks. Achong et al. (22) observed that, although carbohydrate intake was higher in breastfeeding mothers, insulin requirements remained similar, and the incidence of hypoglycemia was low and comparable to that of those using formula feeding.

In addition to lowering insulin doses to 60–70% of pre-pregnancy doses, heightened monitoring and vigilance are recommended in the first postpartum month because most insulin dosing adjustments are made at that time. After that point, most individuals have stable insulin requirements (21).

Hypoglycemia resulting from breastfeeding is rare when the starting blood glucose level is at least 72 mg/dL (17). Hypoglycemic episodes can be reduced by holding feeding until blood glucose is in the recommended range. Using pre-pumped milk as a backup can be an effective strategy when blood glucose is low.

Pharmacological Considerations During Lactation

Most medications enter breast milk through passive diffusion from serum, with few medications actively transported into the breast milk. Concentrations of medications in breast milk are dependent on maternal serum drug concentrations, the size of the molecule, lipophilic qualities, and diffusion characteristics. Medications with poor oral absorption, low lipid solubility, high protein binding, and a short half-life are safest.

The amount of medication in infant serum is dependent on breast milk medication concentration, volume consumed, and infant gastrointestinal absorption. In the early postpartum period, the large spaces between mammary alveolar cells make it easier for medication to pass into the milk. However, this effect is reduced because of the small amount of colostrum consumed. Infant health and maturity are key considerations because more premature or sicker infants can have more deleterious effects from smaller concentrations of medications compared with older, healthier infants (23). Many diabetes medications can be used safely during breastfeeding.

Insulin

Exogenous insulin is the primary medication used by people with type 1 diabetes and is commonly used also for type 2 diabetes. Breastfeeding is compatible with insulin therapy in mothers with diabetes because exogenous insulin, including biosynthetic analogs, is excreted into breast milk and is not harmful to infants, even in preterm populations (24,25). Insulin is a physiological component of human milk and may play a role in neonatal intestinal maturation and immune modulation, potentially reducing the risk of type 1 diabetes in offspring (26). Concentrations of insulin in breast milk are higher in mothers with diabetes than in those without diabetes, with concentrations higher than maternal fasting serum concentrations in people with type 1 diabetes.

Exogenous insulin is not transferred into breast milk in its biologically active form. Moreover, because of its peptide-based structure, insulin undergoes enzymatic degradation within the infant gastrointestinal tract, rendering it inactive. Concentrations of insulin in breast milk decline beginning 3–7 days postpartum. Additionally, there are lower C-peptide levels identified in breast milk compared with serum, suggesting active transport of insulin since its levels in breast milk are as high as or higher than in serum (27,28).

Metformin

Metformin is an oral biguanide that reduces hepatic glucose production, facilitating disposal of glucose in peripheral tissues. Metformin also increases insulin-stimulated glucose uptake in skeletal muscle and adipocytes, resulting in insulin sensitization. Metformin is considered safe to use during lactation. It exhibits low lipid solubility, is excreted relatively quickly (with a mean half-life of 4–5 hours), and shows minimal transfer into breast milk (29–31). Multiple pharmacokinetic studies have reported a relative infant dose well below the 10% threshold of concern (32), with no adverse effects on infant growth or development (33).

Sulfonylureas

Sulfonylureas trigger insulin secretion by acting on an ATP-dependent potassium channel that stimulates depolarization of pancreatic β-cells. Second-generation sulfonylureas such as glyburide and glipizide have low or undetectable concentrations in breast milk. Several studies, including single-dose and repeated-use designs, have shown minimal infant exposure with no hypoglycemia reported (34,35). Nonetheless, infants should be monitored closely when mothers use these medications during breastfeeding given the known potential for hypoglycemia in individuals directly taking these medications.

Other Agents

Thiazolidinediones (TZDs), glucagon-like peptide 1 (GLP-1) receptor agonists, sodium–glucose cotransporter 2 (SGLT2) inhibitors, and dipeptidyl peptidase 4 inhibitors are either insufficiently studied or pose theoretical risks (e.g., kidney injury through dilation of the renal pelvis and tubules in neonates has been seen with SGLT2 inhibitor use) and should generally be avoided or used with extreme caution (35,36). Although many of these medications have favorable properties for lactation (e.g., TZDs are almost fully protein bound [37], and GLP-1 receptor agonists are very large molecules [38] that do not readily transfer into breastmilk), there is a paucity of literature available to support their use.

GLP-1 receptor agonists are of particular interest given a rapid increase in their use outside of the obstetric context, for management of both diabetes and obesity. However, GLP-1 receptor agonists often induce weight loss through neural pathway regulation, which can reduce hunger and food cravings, and delayed gastric emptying, which leads to earlier satiety. This weight loss could theoretically reduce lactation capabilities since the mother may not be able to meet the increased nutritional needs required for breastfeeding (39). Ongoing research is evaluating the safety of these agents during lactation.

Less frequently used antidiabetic medications include α-glucosidase inhibitors, a bile acid–binding resin called colesevelam, and meglitinides. α-Glucosidase inhibitors such as acarbose prevent glucose absorption from the gastrointestinal tract. There are no reports of their use during lactation, so alternative medication is usually recommended, although there is likely minimal transfer into breastmilk given their low bioavailability, large molecular size, and water solubility (40). Colesevelam concurrently treats hypercholesterolemia. It is not absorbed after oral administration and would thus be a consideration for use during lactation. However, there are scant published data to support its safety. Meglitinides stimulate pancreatic release of insulin. They are highly protein bound and thus have poor transfer into breastmilk. However, alternative medication is recommended given their potential to cause hypoglycemia in lactating mothers, and there are few data to support their safety (41).

Nutritional Recommendations

Nutrition counseling and dietary management are crucial components of diabetes care. The goals of adequate nutrition are to balance intake of necessary macro- and micronutrients, regulate glucose without causing hypoglycemia, and promote appropriate weight loss to achieve at least the pre-pregnancy weight or other weight goals. Consultation with a registered dietitian nutritionist (RDN) is strongly recommended. RDNs can provide education, help to create individualized meal plans, and increase individuals’ confidence in their ability to manage their weight.

Breastfeeding increases maternal energy expenditure by ∼450–650 kcal/day. Breastfeeding mothers are advised to consume a minimum of 1,800 kcal/day. Tailored caloric intake can be calculated using the Dietary Reference Intakes Calculator (42). A minimum daily carbohydrate intake of 210 g is recommended to support milk production and minimize hypoglycemia risk (43).

Lactation ketoacidosis can occur in people without diabetes when a low-carbohydrate diet is followed because of depletion of hepatic glycogen stores. To meet energy demands, hepatic gluconeogenesis is stimulated and free fatty acids are mobilized from adipocytes, ultimately with creation of ketones to provide an energy substrate. No cases have been published of lactation ketoacidosis in people with type 1 diabetes; however, ketogenic diets are not recommended during lactation given the theoretical risk (44).

Particularly during nocturnal breastfeeding, planned carbohydrate intake (10–20 g) may help maintain glycemic stability. However, it is unclear how necessary carbohydrate intake is before breastfeeding. In the secondary analysis of the CLIMB RCT by Donovan et al. (17), 95% of nocturnal breastfeeding sessions were not accompanied by carbohydrate intake, yet rates of hypoglycemia were low. Some women may benefit from structured dietary counseling postpartum to align nutritional goals with insulin management strategies.

Interventions to Support Breastfeeding in People With Diabetes

Targeted lactation counseling has been shown to increase breastfeeding initiation and duration among women with type 1 diabetes. Interventions that integrate diabetes education with lactation support, including antenatal classes, individualized insulin adjustment plans, and early postpartum follow-up, may improve outcomes.

Factors associated with higher breastfeeding success include multiparity, participation in prenatal education, and early postpartum follow-up, especially with providers experienced in both diabetes and lactation management (9). Prenatal care through family medicine or midwifery teams has also been correlated with higher breastfeeding rates (9). This care may be considered as a complement to management by a perinatologist and endocrinologist.

People with type 2 diabetes have lower rates of long-term breastfeeding compared with those with type 1 diabetes (45). In resource-poor settings, directing more attention and support to this group may assist in closing breastfeeding gaps.

Countries with more postpartum benefits have demonstrated improved breastfeeding rates. These include longer post-delivery hospital stays, access to lactation education and support, and longer parental leave. In Sweden, 80% of women take parental leave for >9 months, and workplaces have mandated breastfeeding breaks, which has been found to increase rates of exclusive breastfeeding until 6 months postpartum (46). Policies that allow work leave for partners can also increase breastfeeding success because partner support positively influences initiation and continuation of breastfeeding. Conversely, workplaces that impede access to breastfeeding, have inflexible work policies, and lack clean, private lactation rooms can negatively affect breastfeeding continuation (46).

Future Directions

Although insulin pump and CGM technologies have improved glycemic safety during lactation, no standard recommendations exist for insulin titration during breastfeeding. Future research should explore optimal dietary patterns and carbohydrate distribution during lactation and real-time insulin titration algorithms based on CGM.

For nonpregnant individuals, the American Diabetes Association recommends a goal glucose range of 70–180 mg/dL with a goal time in range of ≥70%, <4% of time below 70 mg/dL, and <1% of time below 54 mg/dL (47). The recommended goal glucose range during pregnancy is more restrictive, at 63–140 mg/dL (20). It is unclear whether these goals are appropriate for lactating mothers in the postpartum period. Further research is needed to determine appropriate goals and then find ways to help lactating mothers achieve them.

There are few data on the use of faster-acting insulin during pregnancy and lactation. An ongoing RCT called the CopenFast trial is assessing the use of ultra-rapid-acting insulin (Fiasp) versus rapid-acting insulin (aspart) during pregnancy and lactation (48).

People with diabetes may safely breastfeed their infants. Compassionate and thoughtful management of lactation requires early and frequent assessment of glucose levels and medication in people with diabetes. Providers and patients alike should receive more information and instruction about breastfeeding, particularly with pregestational diabetes, to ensure competent, nuanced postpartum care. Advocacy for increased postpartum health access and workplace support to parents is critical. In conclusion, individuals with diabetes should be supported and encouraged to breastfeed, with careful consideration given to the unique challenges they may encounter in managing their condition alongside the demands of newborn care.