Title: Obesity and Extreme Obesity: New Insights into the Black-White Disparity in Neonatal Mortality
1Obesity 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
2Co-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
3Introduction
- 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
4Introduction
- 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
5Introduction
- 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
6Objectives
- 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
7Materials 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 -
8Materials 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
9Materials 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 lt 35 or 35 years)
- Marital status (married or unmarried)
- Educational status (lt12 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
10Materials 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
11Materials 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)
12Statistical 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
13Statistical 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
14Statistical 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.
15 16Results
- Prevalence of Obesity 9.5
- 12.8 and 8.9 among black and white mothers
respectively p lt0.01 - Class I obesity - 82,603 or 5.9
- Class II obesity - 33,074 or 2.3
- Class III obesity - 17,699 or 1.3
17Results
- Black preponderance regardless of obesity
subclass - Class I (7.5 versus 5.6 p lt0.01)
- Class II (3.2 versus 2.2 p lt0.01)
- Class III (2.1 versus 1.1 p lt0.01)
18Comparison of obese and non-obese mothers by
selected socio-demographic characteristics,
Missouri, 1978-1997
Obese (N133,376) Non-Obese (N1,272,322) P-value
Maternal Age 35 years 10.0 6.4 lt0.01
Parity Multiparous 67.0 57.2 lt0.01
Race Black White 20.7 79.3 14.8 85.2 lt0.01
Education 12 years 80.9 79.2 lt0.01
Married Yes 73.1 75.9 lt0.01
Smoking Yes 22.3 26.2 lt0.01
Adequate Prenatal Care Yes 43.4 39.6 lt0.01
19Prevalence of common obstetric complications
among obese and non-obese women, Missouri,
1989-1997
Obese (N80,044) Non-Obese (N 545,491) p-value
Anemia Yes 899 (1.1) 7513 (1.4) lt0.01
Insulin-dependent diabetes Yes 1308 (1.6) 2068 (0.4) lt0.01
Other forms of diabetes Yes 3773 (4.7) 7906 (1.5) lt0.01
Chronic hypertension Yes 2402 (3.0) 2607 (0.5) lt0.01
Pre-eclampsia Yes 6728 (8.4) 18,721 (3.4) lt0.01
Eclampsia Yes 151 (0.2) 489 (0.1) lt0.01
Placental abruption Yes 494 (0.6) 4171 (0.8) lt0.01
Placental previa Yes 264 (0.3) 2113 (0.4) lt0.01
20Rates of neonatal, early, and late neonatal death
by obesity subclass
21Risk of neonatal, early and late neonatal death
among obese mothers by obesity subclass
Adjusted hazard ratio (95 Confidence Interval) Adjusted hazard ratio (95 Confidence Interval) Adjusted hazard ratio (95 Confidence Interval) 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 lt 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.
22Black-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 Neonatal Early Early Late Late
Adjusted hazard ratio (95 Confidence Interval) Adjusted hazard ratio (95 Confidence Interval) Adjusted hazard ratio (95 Confidence Interval) Adjusted hazard ratio (95 Confidence Interval) Adjusted hazard ratio (95 Confidence Interval) Adjusted hazard ratio (95 Confidence Interval) 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 lt 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.
23Summary
- 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
24Discussion
- 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
25Discussion
- 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
26Limitations
- 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
27Strengths
- 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
28Public 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
29 30References
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20031632146-2148 - Ferraro KF, Thorpe RJ, Jr, Wilkinson JA. The life
course of severe obesity does childhood
overweight matter? J Gerontol B Psychol Sci Soc
Sci. 200358S110-S119 - Fontaine KR, Redden DT, Wang C, Westfall AO,
Allison DB. Years of life lost due to obesity.
JAMA 2003289187-193 - 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
20053521138-1145 - 5. Lin DY, Wei LJ. The robust inference for the
Cox proportional hazards model. J Am Stat Assoc
1989841074-1078
31Acknowledgements
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.
32Contact 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_at_gmail.com