Women's prepregnancy underweight as a risk factor for preterm birth: a retrospective study

Area of Science:

• Obstetrics and Gynecology
• Maternal-Fetal Medicine
• Public Health

Background:

• Maternal underweight is a potential risk factor for adverse pregnancy outcomes.
• Understanding the relationship between the severity of maternal underweight and preterm birth (PTB) is crucial for targeted interventions.

Purpose of the Study:

• To examine how different levels of maternal underweight affect the risk of PTB.
• To determine if the association between maternal underweight and PTB varies by gestational age.

Main Methods:

• A retrospective cohort study analyzed over 950,000 California births from 2007-2010.
• Mothers were categorized by prepregnancy Body Mass Index (BMI): normal, mild (<17.00-18.49 kg/m²), moderate (16.00-16.99 kg/m²), or severe (<16.00 kg/m²).
• Adjusted multivariable Poisson regression estimated the relative risk of PTB.

Main Results:

• Approximately 7.6% of women were underweight.
• A dose-response relationship was observed: PTB rates increased with underweight severity (mild: 7.8%, moderate: 9.0%, severe: 10.2%).
• Risk-adjusted relative risks for PTB were significantly elevated for all underweight categories (mild: 1.22, moderate: 1.41, severe: 1.61).

Conclusions:

• Increasing maternal underweight severity is significantly associated with a higher risk-adjusted risk of preterm birth.
• This association was consistent across spontaneous and medically indicated PTB and across different preterm gestational age groups.