What are the recommendations for a morbidly obese patient with a twin pregnancy and selective fetal growth restriction (sFGR) requiring delivery by 35 weeks regarding the use of low-dose aspirin (acetylsalicylic acid)?

Low-Dose Aspirin in Morbidly Obese Twin Pregnancy with sFGR Requiring Delivery by 35 Weeks

For a morbidly obese patient with twin pregnancy and selective fetal growth restriction requiring delivery by 35 weeks, low-dose aspirin at 100-150 mg daily should have been initiated between 12-16 weeks of gestation and continued until delivery, though starting now (if not already on it) still provides some benefit for maternal preeclampsia prevention despite the advanced gestational age. 1

Current Management at This Gestational Age

If Aspirin Not Yet Started:

• Initiate aspirin 100-150 mg daily immediately, even though the optimal window (<16 weeks) has passed 1, 2
• The higher dose (100-150 mg) is specifically indicated given:
  • Morbid obesity (BMI >40) reduces aspirin effectiveness and requires dose adjustment 3, 1
  • Twin pregnancy may show aspirin non-responsiveness at standard 81 mg dosing, with 67% showing inadequate platelet inhibition 4
  • Multiple high-risk factors present (obesity, twins, sFGR) 1

Aspirin Continuation Until Delivery:

• Continue aspirin daily until delivery at 35 weeks 1, 5
• Do not stop at 36 weeks "just to be safe" - this removes protection during a high-risk period without evidence-based rationale 1
• Low-dose aspirin (75-150 mg) does not increase risks of placental abruption, postpartum hemorrhage, or fetal intracranial bleeding 1, 2

Delivery Planning Considerations

Timing of Aspirin Discontinuation for Cesarean Section:

If cesarean delivery with spinal anesthesia is planned at 35 weeks:

• Discontinue aspirin 7-10 days before the scheduled procedure to allow adequate platelet recovery 5
• Verify platelet count >75 × 10⁹/L immediately before spinal anesthesia 5
• Check coagulation studies given the preeclampsia risk in this clinical scenario 5

Corticosteroids for Fetal Lung Maturity:

• Administer corticosteroids up to 35 weeks 6 days per UK guidelines, though most international guidelines recommend up to 34 weeks 3
• This patient qualifies given planned delivery at 35 weeks 3

Magnesium Sulfate for Neuroprotection:

• Not indicated at 35 weeks - guidelines recommend magnesium sulfate only for delivery <30-33 weeks depending on jurisdiction 3

Evidence-Based Rationale

Why Higher Dose Aspirin Matters in This Patient:

Morbid obesity significantly impairs aspirin efficacy through multiple mechanisms 3:

• Increased aspirin clearance and altered pharmacokinetics in pregnancy
• Higher platelet regeneration rates limiting time-dependent aspirin effects
• Obese women (especially BMI >40) demonstrate higher thromboxane B2 levels and lower rates of complete platelet inhibition 3

Twin pregnancies show aspirin resistance at standard dosing 4:

• 67% of twin pregnancy patients showed normal platelet function (non-response) on 80 mg aspirin versus expected 29% in singletons 4
• Both cases of preeclampsia in the aspirin group had inadequate platelet inhibition 4
• Birth weight differences favored higher dosing though not statistically significant in small pilot study 4

Evidence supports 100-150 mg dosing 1, 2:

• Meta-analyses demonstrate dose-dependent effects with greater reduction in preeclampsia, severe preeclampsia, and FGR at ≥100 mg daily (RR 0.33; 95% CI 0.19-0.57) 1
• International guidelines (FIGO, European) recommend 150 mg for high-risk populations 1
• Standard 81 mg aspirin shows no benefit in chronic hypertension subgroups 3, 1

Twin Pregnancy-Specific Evidence:

Aspirin demonstrates benefit in twin pregnancies 6:

• Significant reduction in preeclampsia (RR 0.48; 95% CI 0.24-0.95) with 100 mg daily 6
• Reduced preterm birth <34 weeks (RR 0.50; 95% CI 0.29-0.86) 6
• Possible reduction in SGA babies (RR 0.74; 95% CI 0.55-1.00) 6
• No increased postpartum hemorrhage risk (RR 0.89; 95% CI 0.35-2.26) 6

Critical Pitfalls to Avoid

Do not use standard 81 mg dosing in this patient - the combination of morbid obesity and twin pregnancy makes this dose inadequate 3, 1, 4

Do not stop aspirin at 36 weeks without specific indication - preeclampsia risk persists through delivery and early postpartum period 1

Do not confuse low-dose aspirin warnings with high-dose aspirin - FDA warnings about third trimester aspirin refer to doses >100 mg for anti-inflammatory purposes, not prophylactic low doses 1, 7

For planned cesarean with spinal anesthesia, coordinate timing carefully - aspirin must be stopped 7-10 days before procedure, but this must be balanced against thrombotic risk during the discontinuation period 5

Verify platelet function before neuraxial anesthesia - particularly important given preeclampsia risk and potential for thrombocytopenia in this clinical scenario 5

Mode of Delivery Considerations

Cesarean section is recommended for severe early-onset FGR 3:

• Guidelines recommend CS for very preterm FGR or severe umbilical artery Doppler abnormalities 3
• Individualize based on Doppler parameters, but CS should be strongly considered at <34-35 weeks with FGR 3
• Continuous fetal monitoring mandatory if attempting labor 3

The combination of twin pregnancy, sFGR, morbid obesity, and delivery at 35 weeks strongly favors planned cesarean delivery 3