At what gestational age is delivery recommended for patients with Gestational Diabetes Mellitus (GDM) type 1 (A1GDM) versus type 2 (A2GDM)?

Timing of Delivery for A1GDM versus A2GDM

For women with A1GDM (diet-controlled), delivery at 38 weeks' gestation is optimal to maximize quality-adjusted life years by balancing the risks of stillbirth against neonatal morbidities, while women with A2GDM (medication-controlled) should be delivered by 39 weeks' gestation. 1, 2

Delivery Timing Recommendations

A1GDM (Diet-Controlled GDM)

• Optimal timing for delivery is 38 weeks' gestation to balance the risk of stillbirth against neonatal complications 1
• Delivery at 38 weeks prevents more stillbirths compared to expectant management to 39 weeks 1
• There is no data supporting delivery before 38 weeks in the absence of maternal or fetal compromise 2
• Prolongation of pregnancy beyond 38 weeks increases the risk of fetal macrosomia without reducing cesarean rates 2

A2GDM (Medication-Controlled GDM)

• Delivery by 39 weeks' gestation is recommended due to increased risks associated with medication-dependent GDM 2
• Women with A2GDM have poorer pregnancy outcomes that more closely approximate pre-existing diabetes 3
• More intensive fetal surveillance is warranted when pregnancy continues beyond 39 weeks 2

Rationale for Timing Differences

• A1GDM has lower risk profile than A2GDM but still carries increased risks compared to normal pregnancies 2
• Decision analysis models show that induction at 38 weeks for A1GDM would prevent 48 stillbirths per 100,000 pregnancies compared to expectant management to 39 weeks 1
• Women with A2GDM have higher rates of:
  • Hypertensive disorders including pre-eclampsia 3
  • Macrosomia and large-for-gestational-age infants 3
  • Need for neonatal intensive care admission 3

Considerations for Mode of Delivery

• GDM alone is not an indication for cesarean delivery 2
• For both A1GDM and A2GDM, consider:
  • Estimated fetal weight (risk of macrosomia increases with advancing gestational age) 2, 4
  • Cervical favorability (unfavorable cervix in multiparous women induced before 39 weeks is associated with higher cesarean rates) 4
  • Parity (nulliparous women have higher cesarean rates regardless of timing) 4

Fetal Surveillance Recommendations

• Women with both A1GDM and A2GDM should be taught to monitor fetal movements during the last 8-10 weeks of pregnancy 2
• For A1GDM with good glycemic control and appropriate fetal growth:
  • Minimal additional surveillance beyond fetal movement monitoring may be needed 2
• For A2GDM:
  • More intensive fetal surveillance is warranted 2
  • Weekly antenatal testing is reasonable after 32 weeks 2

Important Caveats and Pitfalls

• Do not deliver before 38 weeks without evidence of maternal or fetal compromise, as this increases neonatal morbidity without clear benefit 2
• Be aware that cervical favorability significantly impacts cesarean delivery rates, especially in multiparous women induced before 39 weeks (17.4% vs 2.2% cesarean rate with unfavorable vs favorable cervix) 4
• Early GDM (diagnosed before 20 weeks) has worse outcomes despite treatment and may require more aggressive management 5
• Consider intensified fetal surveillance rather than immediate delivery when pregnancy continues beyond 40 weeks 2

Special Circumstances Requiring Earlier Delivery

• Maternal or fetal compromise including:
  • Poor glycemic control despite appropriate therapy 2
  • Hypertensive disorders 2
  • Abnormal fetal testing 2
  • Evidence of fetal growth restriction 2
  • Estimated fetal weight >4500g (increased risk of shoulder dystocia) 2