An obesity paradox in preterm birth: A case control study.

Area of Science:

• Obstetrics and Gynecology
• Public Health
• Epidemiology

Background:

• Preterm birth (PTB) is a leading cause of neonatal mortality, with increasing global rates.
• Existing research on maternal pre-pregnancy body mass index (BMI) and PTB yields inconsistent findings.
• The influence of socioeconomic status (SES) on the BMI-PTB relationship requires further investigation.

Purpose of the Study:

• To investigate the interaction between maternal pre-pregnancy BMI and socioeconomic status (SES) in relation to preterm birth (PTB) rates.
• To address knowledge gaps concerning the complex relationship between BMI, SES, and PTB.
• To evaluate the impact of social class on the association between maternal BMI and PTB.

Main Methods:

• A case-control study design was employed.
• Utilized Natality Data from the National Vital Statistics System (2020-2022).
• Analyzed the relationship between maternal pre-pregnancy BMI, SES, and PTB, incorporating a polynomial BMI term.

Main Results:

• Maternal BMI was a significant factor in PTB for women of lower socioeconomic status (LSES).
• An 'obesity paradox' was observed in LSES women, where increased BMI initially decreased PTB odds (OR=0.923, P<0.001) before rising.
• The BMI-PTB relationship was curvilinear for LSES women, unlike the non-significant association found in higher SES women.

Conclusions:

• The study identified an obesity paradox in preterm birth for lower socioeconomic status mothers.
• The relationship between maternal BMI and preterm birth is curvilinear, not linear, particularly for LSES women.
• Incorporating SES and a polynomial BMI term provides a more nuanced understanding of PTB risk factors.