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?