Are cardiac anomalies or neural tube defects more common in fetuses of obese women?

Cardiac Anomalies Are More Common Than Neural Tube Defects in Fetuses of Obese Women

Cardiac anomalies occur more frequently than neural tube defects in fetuses of obese women, with cardiac defects showing a stronger association with increasing maternal BMI.

Evidence for Increased Risk of Birth Defects in Obese Women

Maternal obesity is associated with an increased risk of various congenital anomalies, with both cardiac defects and neural tube defects being significantly more common compared to women of normal weight. According to current guidelines, rates of congenital anomalies are increased in obese women, particularly involving:

• Cardiovascular anomalies
• Neural tube defects
• Cleft lip or palate
• Anorectal atresia
• Hydrocephaly
• Limb reduction anomalies 1

Comparative Risk: Cardiac vs. Neural Tube Defects

Cardiac Defects

• Obese women (BMI ≥30) have approximately 30% increased risk of cardiovascular anomalies in their offspring (OR: 1.30; 95% CI: 1.12-1.51) 2
• The risk increases with obesity severity:
  • For women with BMI 30-39.9: OR of 1.11 (95% CI: 1.04,1.20)
  • For morbidly obese women (BMI ≥40): OR of 1.33 (95% CI: 1.15,1.54) 3
• Specific cardiac defects with increased risk include:
  • Atrial septal defects
  • Ventricular septal defects
  • Hypoplastic left heart syndrome
  • Aortic stenosis
  • Pulmonic stenosis
  • Tetralogy of Fallot 3
• Prevalence rate ratios for aortic arch defects and transposition of great arteries are doubled in offspring of mothers with severe obesity 4

Neural Tube Defects

• Obese women have an increased risk of neural tube defects with an OR of 1.87 (95% CI: 1.62-2.15) 2
• Specifically for spina bifida, the OR is 2.24 (95% CI: 1.86-2.69) 2
• One study found obese women were 3.5 times more likely to have an infant with spina bifida (95% CI: 1.2-10.3) 5

Frequency Comparison

While the odds ratios for neural tube defects appear higher than for cardiac defects, cardiac defects are overall more common in the general population. The baseline prevalence of congenital heart defects is approximately 0.5-1% of all births 1, whereas neural tube defects occur in approximately 0.1% of births.

In the largest population-based study included in the evidence, among 2,050,491 live births, 28,628 (1.40%) children had at least one congenital heart defect 4, making cardiac defects substantially more common than neural tube defects even in the general population.

Clinical Implications for Obese Pregnant Women

1. Increased Folic Acid Supplementation:

   • Women with BMI >35 kg/m² should take higher doses of folic acid (4-5 mg daily) starting three months before conception and continuing until 12 weeks postconception 1
   • This is specifically to reduce neural tube defect risk

2. Modified Ultrasound Timing:

   • Anatomic survey in obese women should be performed at 20-22 weeks (about 2 weeks later than for normal weight women)
   • If incomplete, follow-up ultrasound should be considered in 2-4 weeks 1

3. Fetal Echocardiography:

   • Fetal echocardiography should be considered for obese pregnant women due to the increased risk of cardiac anomalies 1
   • The risk of cardiac anomalies is increased 9-fold in monochorionic diamniotic twins and up to 14-fold in cases of twin-twin transfusion syndrome 1

Practical Approach for Clinicians

1. Preconception Counseling:

   • Advise weight reduction before pregnancy when possible
   • Prescribe higher dose folic acid (4-5 mg daily) for women with BMI >35 kg/m²
   • Discuss increased risks of both cardiac and neural tube defects

2. Prenatal Screening:

   • Schedule detailed anatomic ultrasound at 20-22 weeks
   • Consider transvaginal approach if visualization is suboptimal
   • Schedule fetal echocardiography to specifically evaluate for cardiac defects
   • Consider follow-up ultrasound if initial study is incomplete

3. Risk Communication:

   • Explain that while the relative risk increase is significant, the absolute risk remains low
   • Emphasize that cardiac defects are more common overall than neural tube defects in obese women

Conclusion

While maternal obesity increases the risk of both cardiac and neural tube defects, cardiac anomalies occur more frequently in absolute numbers due to their higher baseline prevalence. The evidence demonstrates that cardiac defects show a clear dose-response relationship with increasing maternal BMI, with specific cardiac defects being particularly associated with maternal obesity.