The goal of this study is to compare two different thresholds for initiation of medical treatment for GDM. Pregnant women diagnosed with GDM will be randomized to either start pharmacotherapy when they have reached at least 20% or at least 40% of capillary blood glucose (CBG) values above the target goal. The investigators hypothesize that a lower threshold of 20% elevated CBG levels, compared to 40%, will lead to lower rates of obstetric and medical complications.

Gestational diabetes mellitus (GDM) affects 5-8% of pregnant women, many of whom will require treatment beyond diet and exercise. Despite this high prevalence, there is no consensus regarding the glycemic threshold for conversion from diet to medical treatment for GDM. No randomized studies have been performed on how to define failure with diet and exercise and currently, the need to start insulin or oral hypoglycemic agents is at the provider's discretion. It is important to establish criterion of pharmacotherapy initiation for GDM in pregnancy as GDM under-treatment leads to increased rates of adverse obstetric outcomes associated with poor glycemic control including macrosomia, pre-eclampsia, cesarean delivery, shoulder dystocia, birth trauma, neonatal hypoglycemia and hyperbilirubinemia, childhood obesity and metabolic syndrome in the offspring. In contrast, overtreatment for women comes at increased cost due to overutilization of resources, increased expense, and adverse effects of the medications themselves.

The goal of this study is to compare two different thresholds for initiation of medical treatment for GDM. Pregnant women diagnosed with GDM (N=416) will be randomized to either start pharmacotherapy when they have reached at least 20% or at least 40% of capillary blood glucose (CBG) values above the target goal. The investigators hypothesize that a lower threshold of 20% elevated CBG levels, compared to 40%, will lead to lower rates of obstetric and medical complications.

Aim 1: Determine the effect of earlier insulin initiation (20% threshold) for GDM management on adverse neonatal and maternal outcomes associated with GDM.

Hypothesis 1.1: The composite adverse neonatal outcome associated with GDM (LGA, macrosomia, birth trauma, preterm birth, neonatal hypoglycemia, and hyperbilirubinemia) will be lower in earlier insulin initiation compared with the active control group.

Hypothesis 1.2: Preeclampsia and cesarean birth frequencies will be lower in earlier insulin initiation compared with the active control group.

Hypothesis 1.3: The composite neonatal and maternal outcomes will not differ between racial and ethnic groups within each study group.

Aim 2:Assess the safety of earlier insulin initiation in pregnant patients and their neonates.

Hypothesis 2.1: The SGA rate will be higher in earlier insulin initiation compared with the active control group; however, in both groups it will be lower than the national rate of 10%. Hypothesis 2.2: Maternal hypoglycemia and perinatal death will not differ between groups.

Aim 3:Determine the effect of earlier insulin initiation on patient-reported outcomes using standardized measures and qualitative interviews.

Hypothesis 3: Anxiety, depression, perceived stress and diabetes self-efficacy will be better in patients randomized to earlier insulin initiation compared with the active control group.

Inclusion Criteria:

• Viable singleton pregnancy
• Age >= 18 years old
• Diagnosed with gestational diabetes mellitus
• Able to communicate in English

Exclusion Criteria:

• Pre-gestational diabetes
• Significantly abnormal GDM testing, suggestive of the presence of pre-gestational diabetes, either with fasting values >=126 mg/dL or 2-hour post-prandial levels >=200 mg/dL
• Patients who check blood sugars on average less than 2 times per day after appropriate counseling
• Already started pharmacotherapy prior to referral to the study

Only women will be randomized as this is a pregnancy-focused study