What is the most common fetal anomaly in obese pregnant women?

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From the Guidelines

Neural tube defects are the most common fetal anomaly in obese pregnant women. Maternal obesity significantly increases the risk of neural tube defects, with studies showing that obese women have approximately double the risk compared to women of normal weight 1. This increased risk occurs because obesity can interfere with folate metabolism and absorption, which is crucial for proper neural tube development during early pregnancy. Additionally, obesity creates a pro-inflammatory state and metabolic alterations that may adversely affect embryonic development. The neural tube forms very early in pregnancy (by 28 days after conception), often before many women know they're pregnant. Some key points to consider include:

  • Neural tube defects occur in approximately 1 to 2 per 1000 births in the United States 1
  • Anencephaly and spina bifida are the most common types of neural tube defects, occurring with about equal frequency 1
  • Obesity is a significant risk factor for neural tube defects, and weight management before pregnancy can help reduce this risk
  • Folic acid supplementation is crucial in reducing the risk of neural tube defects, and obese women may require a higher dose (4-5 mg daily) compared to women of normal weight 1 To reduce the risk of neural tube defects, obese women planning pregnancy should take a higher dose of folic acid supplementation (4-5 mg daily) and consider weight management before pregnancy. It is essential to note that the neural tube forms very early in pregnancy, often before many women know they're pregnant, highlighting the importance of preconception planning and care.

From the Research

Fetal Anomalies in Obese Pregnant Women

  • The most common fetal anomalies in obese pregnant women include neural tube defects, cardiac anomalies, and orofacial clefts 2.
  • Studies have shown that obese women are at a higher risk of having an infant with neural tube defects, such as spina bifida, compared to women of normal weight 3, 4.
  • Other birth defects that have been associated with maternal obesity include heart defects, omphalocele, and multiple anomalies 4, 5.
  • The risk of neural tube defects, including anencephaly and spina bifida, is higher in obese women, with odds ratios ranging from 1.4 to 3.5 3, 4, 5.
  • Cardiac defects, such as d-transposition of great arteries and tetralogy of Fallot, have also been linked to maternal obesity, although the evidence is not as strong 5.

Specific Fetal Anomalies

  • Neural tube defects:
    • Spina bifida: obese women are at a higher risk of having an infant with spina bifida, with an odds ratio of 2.6 3.
    • Anencephaly: obese women are at a higher risk of having an infant with anencephaly, with an odds ratio of 1.6 5.
  • Cardiac anomalies:
    • Heart defects: obese women are at a higher risk of having an infant with heart defects, with an odds ratio of 2.0 4.
  • Other birth defects:
    • Omphalocele: obese women are at a higher risk of having an infant with omphalocele, with an odds ratio of 3.3 4.
    • Multiple anomalies: obese women are at a higher risk of having an infant with multiple anomalies, with an odds ratio of 2.0 4.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

3
Research

Are obese women at higher risk for producing malformed offspring?

American journal of obstetrics and gynecology, 1994

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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