The lifetime risk of maternal mortality: concept and measurement
John Wilmoth
Volume 87, Number 4, April 2009, 256-262
Table 1. Illustrative calculation of three measures of the lifetime risk of maternal mortality, LR1, LR2 and LR3, based on age-specific maternal mortality data from Bangladesh for 1998–2001
| Age range(years) | Exposure timea | Maternal deathsb | MMRatec (per 1000) | Live births | Fertility rated | MMRatioe (per 100 000) | Life-table exposure timef | LRMM |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Other causes of death ignoredg |
Other causes of death considered |
|||||||||||||||
| From birthh |
From age 15 yearsi |
|||||||||||||||
| LR1 | LR2 | LR3 | ||||||||||||||
| 15–19 | 90 099 | 20.501 | 0.228 | 12 068 | 0.134 | 169.9 | 4.545 | 0.0011 | 0.0010 | 0.0011 | ||||||
| 20–24 | 67 389 | 29.559 | 0.439 | 12 494 | 0.185 | 236.6 | 4.518 | 0.0022 | 0.0020 | 0.0022 | ||||||
| 25–29 | 57 605 | 30.820 | 0.535 | 8 600 | 0.149 | 358.4 | 4.485 | 0.0027 | 0.0024 | 0.0026 | ||||||
| 30–34 | 48 931 | 24.399 | 0.499 | 4 727 | 0.097 | 516.2 | 4.443 | 0.0025 | 0.0022 | 0.0024 | ||||||
| 35–39 | 40 110 | 10.490 | 0.262 | 2 130 | 0.053 | 492.5 | 4.393 | 0.0013 | 0.0011 | 0.0013 | ||||||
| 40–44 | 31 989 | 12.367 | 0.387 | 636 | 0.020 | 1945.9 | 4.337 | 0.0019 | 0.0017 | 0.0019 | ||||||
| 45–49 | 21 880 | 3.256 | 0.149 | 134 | 0.006 | 2435.4 | 4.252 | 0.0007 | 0.0006 | 0.0007 | ||||||
| Totalj | 358 007 | 131.392 | 0.367 | 40 788 | 3.222 | 322.2 | 30.972 | 0.0125 | 0.0111 | 0.0122 | ||||||
LRMM, lifetime risk of maternal mortality; MMRate, maternal mortality rate; MMRatio, maternal mortality ratio.
a Exposure time is the total number of woman-years lived by the survey population during the observation period.
b The numbers of maternal deaths are fractional because they were estimated from survey data using sample weights.
c MMRate = maternal deaths ÷ exposure time.
d Except for the total row, fertility rate = live births ÷ exposure time.
e MMRatio = maternal deaths ÷ live births.
f The life-table exposure time is the number of woman-years lived per female live birth derived from a life table constructed using survey data.
g Except for the total row, elements of the column labelled LR1 = 5 × MMRate = 5 × fertility rate × MMRatio, showing that equivalent measures of lifetime risk can be derived using age-specific values of either the MMRate or the MMRatio.
h Except for the total row, elements of the column labelled LR2 = MMRate × life-table exposure time = fertility rate × MMRatio × life-table exposure time.
i All elements of the column labelled LR3 equal the corresponding element of the column labelled LR2 divided by 0.9115, where 0.9115 is the probability that a female will survive from birth to age 15 years.
j Values in the total row are the sums of their respective column values except for the MMRate, fertility rate and MMRatio. The MMRate for ages 15–49 years combined equals total maternal deaths divided by total exposure time; similarly, the MMRatio for ages 15–49 years combined equals total maternal deaths divided by total live births. Finally, the sum of fertility rates by 5-year age groups is multiplied by 5 to represent the total fertility rate (TFR) or the hypothetical average number of births per woman according to the age-specific birth rates observed in the survey population, under the assumption that death does not occur before menopause.All data are from the Bangladesh Maternal Health Services and Maternal Mortality Survey of 2001.7 Data in the columns labelled Exposure time to MMRatio were taken or derived from table 3.2 of that report. The life-table exposure time and the probability that a female will survive to age 15 years (see note i) were derived by computing a female life-table using all-cause death rates as shown in table 3.8 of that report.