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


1
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

2
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

3
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

4
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

5
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

6
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

7
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

8
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

9
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 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

10
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

11
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)

12
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

13
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

14
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.

15
  • RESULTS

16
Results
  • 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

17
Results
  • 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)

18
Comparison 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
19
Prevalence 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
20
Rates of neonatal, early, and late neonatal death
by obesity subclass
21
Risk 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.
22
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 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.
23
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

24
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

25
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

26
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

27
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

28
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

29
  • THANKS

30
References
  • Sturm R. Increases in clinically severe obesity
    in the United States, 1986-2000. Arch Intern Med
    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

31
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.
32
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_at_gmail.com
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