An obesity paradox in preterm birth: A case control study
Krystal Hunter1,2,3, Michael Ehrlich3, Jocelyn Mitchell-Williams4,5
1Department of Medicine, Cooper Medical School of Rowan University, Camden, New Jersey, United States of America.
Insights
Maternal pre-pregnancy body mass index (BMI) impacts preterm birth (PTB) differently based on socioeconomic status. Lower socioeconomic status women show an obesity paradox, with a curvilinear relationship between BMI and PTB risk.
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.
Abstract:
The March of Dimes Global action report indicated that preterm birth (PTB) rates are increasing in most countries. It is the most important cause of neonatal deaths and the second leading cause of death in children under age 5. Literature reporting the relationship between maternal pre-pregnancy body mass index (BMI) and PTB has previously yielded inconsistent conclusions. Our objective is to fill in the knowledge gap by evaluating the interaction of socio-economic status (SES) and BMI and its relationship to the rate of PTB. This is a case control study using the Natality Data of the National Vital Statistics System from the years 2020-2022. BMI was a significant factor in PTB for lower socioeconomic status (LSES) women. For every increase in BMI, there was a decrease in the probability of PTB (OR = 0.923, 95% CI 0.915-0.931, P < 0.001). Those who were LSES also had a curved relationship with PTB indicating that the as BMI increases, the odds of PTB decreases up until a BMI value, then the PTB rate increases. This relationship was not found in higher economic status women. Our study had two significant findings. We first found an obesity paradox in PTB for those mothers who are LSES. We also found that the relationship between BMI and PTB was not linear but curvilinear, bridging the gap in the conclusions of other studies. This study fills in the knowledge gap of BMI and PTB by adding the consideration of social class and by creating a polynomial BMI term.
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