Reproduction, health and mortality in Gambian women Rebecca Sear London School of Economics Ruth...
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Transcript of Reproduction, health and mortality in Gambian women Rebecca Sear London School of Economics Ruth...
Reproduction, health and mortality in Gambian women
Rebecca Sear
London School of Economics
Ruth Mace, University College London
Relationships between reproduction, health and mortality
1. Reproduction requires minimum body condition – predicts body condition will be positively correlated with successful reproduction
2. But reproduction costly – predicts reproduction should cause reduction in body condition and ultimately increase mortality rates
– maternal depletion– costs of reproduction
Study site
The Gambia
Data
• Collected from 4 rural villages since 1950
• Demographic, anthropometric and genealogical data
• Until 1975 both fertility & mortality were high
– TFR ~ 7, 5q0 ~ 0.43
• After 1975 mortality dropped, but fertility remained high
Summary of anthropometry
Non-pregnant adult women (n~11,600 measurements):
Mean Min Max
Weight (kg) 51.48 24.09 99.34
Height (cm) 157.71 122.55 178.43
BMI 20.67 12.37 39.74
Hb (g/dl) 11.8 2.0 17.1
Age (yrs) 39.61 21 90
Evidence for costs of reproduction?
• Is reproductive effort correlated with mortality rate for women?
• Samples:
– reproductive-aged women, 15-49 years (~1000)
– post-reproductive women, 50+ years (~400)
Measures of reproductive effort
• Giving birth
• Parity
• Timing of reproduction – age at first birth – age at last birth
• Intensity of reproductive effort– pace of reproduction– twins– boys
Mortality: reproductive-aged women• Discrete-time event-history
analysis • Analysing effects of:
– giving birth– parity– timing: age at first birth– intensity:
• sex of most recent birth• twins
• Controlling for birth cohort
Results of mortality model: 15-49 yrs
Variable Model 1
OR p
Age 1.06 <0.01
Birth year 2.09 <0.01
Parity 0.83 <0.01
Age first birth (ref 18-19): <18 >19
0.731.37
NSNS
Mother of twins 0.66 NS
NS:
• intensity of reproductive effort: whether most recent birth was twin or male
Mortality: post-reproductive women
• Discrete-time EHA
• Analysing effects of:– parity– timing:
• age at first birth
• age at last birth
– intensity:• pace
• twins
• sons
Mortality and parity
Age (years)
1009080706050
Pro
port
ion li
ving
1.0
.8
.6
.4
.2
0.0
Births
8+
4-7
1-3
Median age at death (yrs)
80
76
69
Mortality and age at last birth
Age (years)
1009080706050
Pro
port
ion
surv
ivin
g1.0
.8
.6
.4
.2
0.0
40+
<40
Median age at death (yrs)
77
72
Results of mortality model: 50+ yrsVariable Model 1
OR pAge 1.12 <0.01Parity 0.97 NSNulliparous 1.46 NSAge first birth (ref 18-19): <18 >19
1.151.47
NS0.057
Age last birth (ref 30-39): <30 >39
1.120.42
NS<0.01
Mother of twins 3.55 <0.01
NS:
• sex composition
Conclusions
• Evidence for costs of reproduction inconclusive
• Mortality:
– Giving birth clearly a risk factor
– But other evidence suggests negative relationship between reproduction and mortality
– EXCEPT twin mothers have higher post-reproductive mortality
Selection effects?
• Potential explanation for negative relationship between reproduction and mortality:– only healthy women can reach high parities, start
reproducing early and stop reproducing late
– less healthy women start later, stop earlier and have fewer births
• Solutions?– control for health in mortality analysis
– use repeated measures anthropometric data
Controlling for health: 15-49 yrs
Variable Model 1 Model 2
OR p OR p
Age 1.06 <0.01 1.11 <0.01
Birth year 2.09 <0.01 2.67 <0.01
Parity 0.83 <0.01 0.74 <0.01
Age first birth (ref 18-19): <18 >19
0.731.37
NSNS
0.961.57
NSNS
Mother of twins
BMI before first birth
0.66 NS 0.98
0.90
NS
NS
Controlling for health: 50+ yrsVariable Model 1 Model 2
OR p OR pAge 1.12 <0.01 1.20 <0.01Parity 0.97 NS 0.94 NSNulliparous 1.46 NS 1.20 NSAge first birth (ref 18-19): <18 >19
1.151.47
NS0.057
1.231.46
NS0.070
Age last birth (ref 30-39): <30 >39
1.120.42
NS<0.01
1.120.46
NS<0.01
Mother of twins
Height
3.55 <0.01 2.99
0.99
<0.01
NS
Selection effects?
• Potential explanation for negative relationship between reproduction and mortality:– only healthy women can reach high parities, start
reproducing early and stop reproducing late
– less healthy women start later, stop earlier and have fewer births
• Solutions?– control for health in mortality analysis
– use repeated measures anthropometric data
Conclusions
• Controlling for health does not affect relationship between reproduction and mortality:
– inadequate measures of health?
– protective effects of reproduction?