The purpose of this study is to learn about how breast milk from mothers with insulin-resistance may be different. Investigators are specifically studying insulin concentrations in breast milk. Investigators are also studying how insulin in breast milk might affect a baby's intestines and pancreas.

Inclusion Criteria:

• Mothers ≥ 19 years of age

• Mothers intending to Exclusively Breastfeed for at least 5months

• Mothers comfortable with feeding their infants expressed breast milk from a bottle at 2-weeks postpartum

• Trial of labor (no scheduled C-sections)

• Singleton birth

• Healthy Infants

• "Normal Weight" will be defined as pre-pregnant BMI between 18.5-23.9 kg/m2 and passing the 28 week oral glucose tolerance test.

• "Insulin Resistance" will be defined as meeting any of the following:

  • pre-pregnant BMI ≥ 28 and failed the 28 week oral glucose screening test
  • pre-pregnant BMI ≥ 28 and diagnosis of either A1 ("diet controlled") or A2 ("insulin-requiring") gestational diabetes during pregnancy, but insulin therapy discontinued after birth.
  • pre-pregnant BMI ≥ 28 and diagnosed with type 2 diabetes during pregnancy
  • pre-pregnant BMI ≥ 30, and unmediated.

Exclusion Criteria:

• Scheduled C-sections or emergency C-sections with no labor (natural or induced)
• Maternal insulin therapy after birth
• Significant maternal health concern including type 1 diabetes, renal, kidney, thyroid, or cardiovascular disease, pre-eclampsia, or other disease.
• Delivery before 37 weeks
• Infant birth weight <2500g
• Infant medical or genetic indications that would impact normal feeding behavior, insulin signaling or growth patterns
• Infant supplementation with infant formula (glucose gel or donor milk is acceptable)

The inclusion criteria were selected to include only healthy infants of uncomplicated pregnancy (with the exception of gestational diabetes) and normal birth weight. The criteria for insulin resistance were strategically defined to capture the insulin-resistant population which represents a large proportion of the population that are at risk for diabetes but have not yet developed the disease. Insulin therapy is an exclusion criteria because it passes through the breast milk and we are unable to distinguish endogenous maternal insulin from exogenous therapeutic insulin in breast milk samples. These criteria will minimize the risks and increase the safety of subjects.