Diabetes in Pregnancy

Summary

Diabetes in pregnancy includes gestational diabetes, developing in mid-pregnancy, and pregestational diabetes, present before conception. Both increase maternal risks (hypertension, cesarean delivery) and fetal risks (macrosomia, anomalies, neonatal hypoglycemia). Diagnosis is by glucose tolerance testing, and management involves diet, glucose monitoring, insulin if needed, and close fetal surveillance. GDM usually resolves postpartum but carries a high risk of recurrence and future type 2 diabetes

Definition

Diabetes in pregnancy refers to glucose intolerance identified during gestation and includes two major categories: gestational diabetes mellitus (GDM) and pregestational diabetes mellitus (type 1 or type 2 diabetes diagnosed before conception). GDM is defined as any degree of glucose intolerance with onset or first recognition during pregnancy, typically manifesting in the second or third trimester. Pregestational diabetes carries higher risks for both mother and fetus, particularly because hyperglycemia during early organogenesis predisposes to congenital malformations.

Epidemiology

GDM complicates approximately 4% of pregnancies, whereas pregestational diabetes is present in about 1%. GDM usually resolves postpartum but significantly increases the risk of developing type 2 diabetes later in life (∼50% within 10 years).

Pathophysiology

Pregnancy is a diabetogenic state characterized by altered insulin dynamics:

• First trimester: Increased insulin sensitivity → risk of hypoglycemia.

• Second and third trimesters: Placental hormones (human placental lactogen, progesterone, estrogen, cortisol, prolactin) induce progressive insulin resistance, leading to postprandial hyperglycemia.

• Women with limited pancreatic reserve cannot compensate, resulting in gestational diabetes.

• After delivery, insulin resistance declines and most cases of GDM resolve.

Risk Factors

• Maternal obesity (BMI > 30–35)

• Advanced maternal age (> 30–35 years)

• Family history of type 2 diabetes

• Previous GDM or impaired glucose tolerance

• Previous macrosomic infant (> 4.5 kg)

• Recurrent pregnancy loss or unexplained stillbirth

• Polycystic ovarian syndrome

• Certain ethnic groups (e.g., Asian, Middle Eastern, Hispanic)

Clinical Features

Most women are asymptomatic, and GDM is usually detected by screening. Warning signs may include polyhydramnios or large-for-gestational-age fetuses (>90th percentile). Pregestational diabetes may present with hypoglycemia, hyperglycemia, or complications of chronic diabetes (e.g., retinopathy, nephropathy).

Screening and Diagnosis

• Universal screening for GDM: at 24–28 weeks gestation.

• Early testing: 16 weeks in high-risk women (e.g., obesity, previous GDM) to rule out pregestational diabetes.

• Oral glucose tolerance test (OGTT):

• 50 g glucose load (screening, non-fasting): abnormal if ≥140 mg/dL at 1 hour.

• Diagnostic OGTT (75 g or 100 g, fasting): GDM diagnosed if ≥2 abnormal values: 

• Fasting ≥92–95 mg/dL

• 1 h ≥180 mg/dL  for 100 g

• 2 h ≥153–155 mg/dL  for 100 g

• 3 h ≥140 mg/dL for 100 g

Complications

Maternal

• Hypertensive disorders of pregnancy (preeclampsia, eclampsia)

• Polyhydramnios

• Preterm labor

• Postpartum hemorrhage

• Urinary tract infections

• Increased cesarean delivery rates

• Hypoglycemia or hyperglycemic crises

• Worsening of pre-existing diabetic complications (retinopathy, nephropathy, neuropathy)

• Long-term risk of type 2 diabetes

Fetal and Neonatal

Diabetic Embryopathy (more common in pregestational DM, first trimester):

• Early pregnancy loss, perinatal death

• Neural tube defects (anencephaly, spina bifida)

• Congenital heart disease (transposition of great vessels, VSD (most common), truncus arteriosus, coarctation of the aorta)

• Caudal regression syndrome (sacral agenesis), most specific.

• Renal, skeletal, gastrointestinal, and craniofacial anomalies

Diabetic Fetopathy (more common in GDM and pregestational DM in later pregnancy):

• Fetal macrosomia and organomegaly

• Neonatal hypoglycemia (due to persistent hyperinsulinemia)

• Polycythemia and hyperbilirubinemia

• Hypocalcemia, hypomagnesemia

• Respiratory distress syndrome, transient tachypnea, perinatal asphyxia

• Hypertrophic cardiomyopathy (due to fat and glycogen deposition in the myocardium)
  

Management

The goal is tight maternal euglycemia to prevent maternal and fetal complications.

• Lifestyle: Medical nutrition therapy, weight control, and regular physical activity.

• Glucose monitoring: Four times daily, with targets fasting <90 mg/dL and postprandial <120–140 mg/dL.

• Medication:

• Insulin is the preferred treatment if lifestyle measures fail.

• Metformin or glyburide may be considered when insulin is not feasible.

• Fetal monitoring: Serial ultrasounds at 28, 32, and 36 weeks for growth, amniotic fluid, and well-being; NST or biophysical profile after 32 weeks if risk factors are present.

• Delivery planning:

• Induction at 38–39 weeks if on treatment.

• Cesarean section recommended if estimated fetal weight > 4500 g in diabetic women.

• Blood glucose should be controlled intrapartum with IV insulin/dextrose infusion.

• Postpartum care: Stop pharmacologic therapy immediately after delivery, check glucose before discharge, and perform an OGTT 4–12 weeks postpartum; repeat screening every 1–3 years.
  

Prognosis

• Most cases of GDM resolve after delivery, but recurrence occurs in ~50% of subsequent pregnancies.

• Women with GDM have up to 50% risk of developing type 2 diabetes within 10 years.

• Offspring of diabetic mothers are at risk of obesity, metabolic syndrome, and type 2 diabetes later in life.