# Presentation: 726447

## Obesity and Extreme Obesity: New Insights into the Black-White Disparity in Neonatal Mortality

- Hamisu M. Salihu, MD, PhD
- Department of Epidemiology and Biostatistics
- &
- Department of Obstetrics and Gynecology
- University of South Florida

## Co-Authors:

- Amina P. Alio, PhD
- Council on African American Affairs, Washington, DC
- Roneé E. Wilson, MPH
- Department of Epidemiology and Biostatistics, University of South Florida
- Russell S. Kirby, PhD
- Department of Maternal and Child Health, University of Alabama at Birmingham, Birmingham, AL
- Greg R. Alexander, ScD
- Department of Pediatrics, University of South Florida

## Introduction

- During the past two decades, the prevalence of obesity has been rising continuously in the United States, especially among women1
- Between 1986 to 2000 the prevalence of obesity, defined as body mass index (BMI) ≥30, doubled, while that of morbid or extreme obesity quadrupled2

## Introduction

- As a result of the increases in BMI and the strong association between obesity and years of life lost3, some authors have predicted that the steady increase in life expectancy that marked the 20th century may halt in the 21st century4
-  Absent in the ongoing debate on the impact of obesity on longevity is any discussion of the effect of maternal obesity on survival chances of the offspring

## Introduction

- Information on the association between obesity and neonatal survival is scant
- Risk estimates in the published literature are derived from highly homogenous populations
- May not have practical application in the racially/ethnically diverse populace of the United States

## Objectives

- To determine the impact of maternal obesity on neonatal survival
- To examine gradations of obesity as well as obesity-related black-white disparity in neonatal survival

## Materials and Methods

- Missouri maternally linked cohort data files were used covering the period from 1978 through 1997
- Singleton live births within the gestational age range of 20-44 weeks were selected
- Body mass index [weight (in kilograms) divided by height (in metres2)] was used to define maternal pre-pregnancy weight groups

## Materials and Methods

- Women were assigned to the following BMI-based categories:
- Normal (18.5-24.9)
- Class I obesity (30.0-34.9)
- Class II obesity (35.0-39.9)
- Class III (morbid/extreme obesity) (≥40)
- Underweight mothers were excluded

## Materials and Methods

- Differences between obese and non-obese mothers in socio-demographic features were examined using the following characteristics:
- Race (categorized as black or white)
- Maternal age (categorized as < 35 or ≥35 years)
- Marital status (married or unmarried)
- Educational status (<12 or ≥12 years)
- Cigarette smoking during pregnancy (yes or no)
- Adequacy of prenatal care (adequate or inadequate)
- assessed using the revised graduated index algorithm
- based on the trimester prenatal care began, number of visits, and the gestational age of the infant at birth

## Materials and Methods

- Documentation of certain morbidities on United States birth certificates did not become official until 1989
- Thus, comparison of the following complications was restricted to the period 1989 through 1997:
- Anemia
- Insulin-dependent diabetes mellitus
- Other types of diabetes mellitus
- Chronic hypertension
- Pre-eclampsia
- Eclampsia
- Abruptio placenta
- Placenta previa

## Materials and Methods

- The outcome of interest was neonatal mortality
- defined as death occurring from the day of birth (day 0) to 27 days after birth (day 27)
- further subdivided into:
- early neonatal mortality (from day 0 to day 6)
- late neonatal mortality (from day 7 to day 27)

## Statistical Analysis

- Neonatal mortality rates were computed by dividing the number of neonatal deaths by total live births and multiplying by 1000
- Chi-square test was used to determine differences in socio-demographic characteristics and maternal pregnancy complications between obese and non-obese mothers
- Chi-square for trend was applied to assess a dose-response relationship between severity of maternal obesity and neonatal mortality

## Statistical Analysis

- Cox Proportional Hazards Regression models were used to generate risk estimates after confirming the non-violation of the proportionality assumption
- Adjusted hazards ratios were derived by loading all variables considered to be potential confounders into the model
- The Robust Sandwich estimator was used to adjust for intracluster correlation because the dataset contained successive pregnancies5

## Statistical Analysis

- All tests of hypothesis were two-tailed with a type 1 error rate fixed at 5%
- SAS version 9.1 (SAS Institute, Cary, NC) was used to perform all analyses
- Study was approved by the Office of the Institutional Review Board at the University of South Florida.

## 

RESULTS

- RESULTS

## Results

- Prevalence of Obesity = 9.5%
- 12.8% and 8.9 % among black and white mothers respectively; p <0.01
- Class I obesity - 82,603 or 5.9%
- Class II obesity - 33,074 or 2.3%
- Class III obesity - 17,699 or 1.3%

## Results

- Black preponderance regardless of obesity subclass:
- Class I (7.5% versus 5.6%; p <0.01)
- Class II (3.2% versus 2.2%; p <0.01)
- Class III (2.1% versus 1.1%; p <0.01)

## Comparison of obese and non-obese mothers by selected socio-demographic characteristics, Missouri, 1978-1997

|  | Obese 
(N=133,376)
             % | Non-Obese (N=1,272,322)
              % | P-value |
| --- | --- | --- | --- |
| Maternal Age
    ≥ 35 years  | 
10.0 | 
6.4 | 
<0.01 |
| Parity 
     Multiparous | 
67.0 | 
57.2 | 
<0.01 |
| Race 
      Black
      White | 
20.7
79.3 | 
14.8
85.2 | 
<0.01 |
| Education
       ≥ 12 years  | 
80.9 | 
79.2 | 
<0.01 |
| Married 
       Yes | 
73.1 | 
75.9 | 
<0.01 |
| Smoking 
       Yes | 
22.3 | 
26.2 | 
<0.01 |
| Adequate Prenatal Care
        Yes | 
43.4 | 
39.6 | 
<0.01 |

## Prevalence of common obstetric complications among obese and non-obese women, Missouri, 1989-1997

|  | Obese (N=80,044) % | Non-Obese (N= 545,491) % | p-value |
| --- | --- | --- | --- |
| Anemia
     Yes | 
899 (1.1) | 
7513 (1.4) | 
<0.01 |
| Insulin-dependent diabetes 
      Yes | 
1308 (1.6) | 
2068 (0.4) | 
<0.01 |
| Other forms of diabetes 
      Yes | 
3773 (4.7) | 
7906 (1.5) | 
<0.01 |
| Chronic hypertension 
      Yes  | 
2402 (3.0) | 
2607 (0.5) | 
<0.01 |
| Pre-eclampsia
      Yes | 
6728 (8.4) | 
18,721 (3.4) | 
<0.01 |
| Eclampsia
      Yes | 
151 (0.2) | 
489 (0.1) | 
<0.01 |
| Placental abruption
      Yes | 
494 (0.6) | 
4171 (0.8) | 
<0.01 |
| Placental previa
      Yes | 
264 (0.3) | 
2113 (0.4) | 
<0.01 |

## Rates of neonatal, early, and late neonatal death by obesity subclass

## Risk of neonatal, early and late neonatal death among obese mothers by obesity subclass

| Adjusted hazard ratio (95% Confidence Interval) |  |  |  |
| --- | --- | --- | --- |
|  | *Neonatal | *Early neonatal | Late neonatal |
| Normal weight
(BMI =18.5 – 24.9) | 1.0 | 1.0 | 1.0 |
| Overall obesity | 1.2 (1.1-1.2) | 1.2 (1.1-1.3) | 1.1 (0.9-1.3) |
| Class I obesity
(BMI =30 – 34.9) | 1.1 (1.0-1.2) | 1.1 (1.0-1.2)  | 0.9 (0.8-1.2) |
| Class II obesity
(BMI =35 – 39.9) | 1.2 (1.1-1.4) | 1.2 (1.1-1.4) | 1.3 (1.0-1.8) |
| Class III obesity
(BMI ≥40) | 1.3 (1.1-1.5) | 1.3 (1.1-1.5) | 1.3 (0.9-1.9) |

- *P value for trend < 0.01
- Note: Adjusted hazard ratios were obtained after controlling for the effects of maternal race, age, educational achievement,
- marital status, smoking habits during pregnancy, adequacy of prenatal care received, fetal gender and year of birth.

## Black-White disparity risk for neonatal, early and late neonatal mortality associated with obesity [normal weight white mothers (18.5-24.9) are the referent category]

|  | Neonatal |  | Early |  | Late |  |
| --- | --- | --- | --- | --- | --- | --- |
| Adjusted hazard ratio (95% Confidence Interval) |  |  |  |  |  |  |
|  | *Black | White | *Black | White | *Black | White |
| Overall Obesity | 
1.8 
(1.6-2.0) | 
1.0 
(0.9-1.1) | 
1.8 
(1.6-2.0) | 
1.0 
(0.9-1.1) | 
1.6 
(1.2-2.1) | 
0.9 
(0.8-1.2) |
| Class I | 
1.6 
(1.3-1.8) | 
0.9 
(0.8-1.1) | 
1.6 
(1.3-1.9) | 
1.0 
(0.9-1.1) | 
1.5 
(1.0-2.1) | 
0.8 
(0.6-1.0) |
| Class II | 
1.9 
(1.5-2.4) | 
1.1 
(0.9-1.3) | 
2.0 
(1.5-2.5) | 
1.1 
(0.9-1.3) | 
1.6 
(1.0-2.8) | 
1.2 
(0.9-1.8) |
| Class III | 
2.0 
(1.4-2.4) | 
1.1 
(0.9-1.4) | 
1.9 
(1.4-2.5) | 
1.1 
(0.8-1.4) | 
1.9 
(1.0-3.4) | 
1.1 
(0.7-1.9) |

- *P for trend < 0.01; N = number of deaths
- Note: Adjusted hazard ratios were obtained after controlling for the effects of maternal age, educational achievement, marital status, smoking habits during pregnancy, adequacy of prenatal care received, fetal gender and year of birth.

## Summary

- We found an association between maternal obesity and neonatal mortality
- The positive association restricted only to obese black mothers. White obese mothers did not show an association
- The higher the gradation of obesity the more pronounced the black-white risk differential for neonatal mortality
- Early rather than late neonatal death appears to be the major contributor to the preponderance of neonatal deaths among obese black mothers

## Discussion

- A potential explanation for the black-white disparity is differences in access to care
- However, after adjusting for the adequacy of prenatal care received, the disparity still persisted
- indicating that the obesity-associated black-white disparity in neonatal mortality is independent of access to prenatal care
- Nonetheless, access to care cannot be dismissed as a factor, because the adequacy of prenatal care index does not take into account the quality of care received

## Discussion

- Results showed a higher frequency of diabetes, chronic hypertension and pre-eclampsia among obese women for those years for which data were officially available in the United States
- Contribution of these complications to adverse outcomes on the infant as reported in the literature remains unclear
- However, our findings did not indicate that diabetes and hypertensive disorders might partially explain the association between maternal BMI and adverse pregnancy outcomes

## Limitations

- Long period of follow-up which spanned almost 20 years
- Different infant cohorts were aggregated and analyzed together
- Exposure to varying obstetric practices across the period of study, thus the findings might have been impacted by this cohort effect
- However, by controlling for year of birth in computing adjusted hazard estimates the influence of this potential source of bias on our results was minimized considerably
- Inability to separate black and white non-Hispanics from Hispanics because of the non-differentiation of ethnicity across this categorization in many of the records

## Strengths

- Population-wide study
- Therefore, the results are minimally affected by selection biases (e.g., referrals, etc), a source of concern in data derived from individual health facilities
- The findings are reasonably generalizable
- This work adds new data to a domain that is still poorly understood and under-researched

## Public Health Implications

- The findings of this study have considerable implications in defining areas of intervention to reduce the persistent black-white disparity in neonatal and infant mortality in the United States
- Since obesity is a modifiable condition, targeting obese black women to reduce weight in the pre-conceptional period could be a useful and reasonable primary prevention strategy to curtail the excess neonatal mortality risks in blacks

## 

THANKS

- THANKS

## References

- Sturm R. Increases in clinically severe obesity in the United States, 1986-2000. Arch Intern Med 2003;163:2146-2148
- Ferraro KF, Thorpe RJ, Jr, Wilkinson JA. The life course of severe obesity: does childhood overweight matter? J Gerontol B Psychol Sci Soc Sci. 2003;58:S110-S119
- Fontaine KR, Redden DT, Wang C, Westfall AO, Allison DB. Years of life lost due to obesity. JAMA 2003;289:187-193
- Olshansky SJ, Passaro DJ, Hershow RC et al. A potential decline in life expectancy in the United States in the 21st century. N Engl J Med 2005;352:1138-1145
- 5.	Lin DY, Wei LJ. The robust inference for the Cox proportional hazards model. J Am Stat Assoc 1989;84:1074-1078

## Acknowledgements

- This work was supported through a Young Clinical Scientist Award to Dr. Hamisu Salihu by the Flight Attendant Medical Research Institute (FAMRI). The funding agency did not play any role in any aspect of the study. The rest of the authors have no financial or conflict of interest disclosures to make. We thank the Missouri Department of Health and Senior Services for providing the data files used in this study.

## Contact Information

- Hamisu Salihu, MD, PhD
- COPH
- 13201 Bruce B. Downs Blvd., MDC 56
- Tampa, Florida 33612-3805
- Tel: (205) 910-8720 / Fax: (813) 974-4719
- E-mail: hamisu.salihu@gmail.com