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Mortality rate Crude Death Rate (CDR) Infant Mortality Rate (IMR) Maternal Mortality Ratio (MMR) Neonatal Mortality Rate (NMR) Perinatal Mortality Rate (PMR) Under-5 Mortality Rate Explain each with example

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Mortality Rates and Ratios - Complete Guide

(Source: Park's Textbook of Preventive and Social Medicine)

1. Crude Death Rate (CDR)

Definition: The number of deaths (from all causes) per 1000 estimated mid-year population in one year, in a given place.
Formula:
CDR = (Number of deaths during the year / Mid-year population) × 1000
Example: If a city has a mid-year population of 500,000 and records 3,500 deaths in a year:
CDR = (3,500 / 500,000) × 1000 = 7 per 1000
Key points:
  • The simplest measure of mortality
  • Considered a fair indicator of the comparative health of a population
  • Major limitation: Lacks comparability between communities with different age, sex, or racial compositions. A younger population (like most developing countries) will show a low CDR even if its age-specific death rates are high - this is misleading
  • Should always be examined first, followed by age-specific death rates

2. Infant Mortality Rate (IMR)

Definition: "The ratio of infant deaths registered in a given year to the total number of live births registered in the same year; expressed as a rate per 1000 live births."
Formula:
IMR = (Deaths of children < 1 year of age in a year / Live births in the same year) × 1000
Example: If there are 200,000 live births in a state and 4,000 infants die before completing 1 year of age:
IMR = (4,000 / 200,000) × 1000 = 20 per 1000 live births
Key points:
  • Universally regarded as the most important single indicator of community health status and level of living
  • Also reflects effectiveness of MCH (Maternal and Child Health) services
  • Given special importance because: (a) it is the largest single age-category of mortality; (b) infant deaths arise from a peculiar set of diseases/conditions; (c) IMR changes rapidly in response to specific health programmes
  • India's IMR was 88 (1990) and declined to 32 (2018); Japan's is as low as 2 per 1000

3. Maternal Mortality Ratio (MMR)

Definition (WHO): "The death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of duration and site of pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from unintentional or incidental causes."
Formula:
MMR = (Total female deaths due to complications of pregnancy/childbirth/within 42 days of delivery / Total live births in the same area and year) × 100,000
(Note: expressed per 100,000 live births)
Example: If a country has 500,000 live births in a year and 250 maternal deaths:
MMR = (250 / 500,000) × 100,000 = 50 per 100,000 live births
Types of maternal deaths:
  • Direct obstetric deaths: From obstetric complications (e.g., haemorrhage, hypertensive disorders, anaesthesia complications)
  • Indirect obstetric deaths: From pre-existing disease aggravated by pregnancy (e.g., cardiac or renal disease made worse by pregnancy)
  • Late maternal death: Death from direct/indirect obstetric causes after 42 days but within 1 year of termination of pregnancy
Key points:
  • MMR is a fine measure of the quality of maternity services
  • India's National Population Policy 2000 target: reduce MMR to below 100 per 100,000 live births
  • Note: It is technically a ratio (not a rate), because the denominator (live births) does not represent the population truly "at risk" of maternal death

4. Neonatal Mortality Rate (NMR)

Definition: The number of neonatal deaths (deaths occurring from birth up to 28 completed days of life) per 1000 live births in the same year.
Formula:
NMR = (Deaths of children under 28 days of age in a year / Total live births in the same year) × 1000
Example: If there are 100,000 live births in a district and 1,200 neonatal deaths in that year:
NMR = (1,200 / 100,000) × 1000 = 12 per 1000 live births
Key points:
  • The neonatal period (0-28 days) is the most vulnerable time for child survival
  • NMR reflects the intensity of endogenous factors (e.g., low birth weight, birth injuries, congenital anomalies)
  • Causes: Prematurity + congenital anomalies = ~60% of deaths; birth asphyxia = ~25% (mainly first week); infections (diarrhoea, tetanus) dominate in the late neonatal period
  • Intrapartum complications, low birth weight, and preterm birth account for 60% of neonatal deaths

5. Perinatal Mortality Rate (PMR)

Definition: Perinatal mortality includes both late foetal deaths (stillbirths) and early neonatal deaths. The perinatal period runs from the 28th week of gestation to the 7th day after birth.
Formula (WHO - for countries with established vital records):
PMR = (Late foetal deaths [≥28 weeks gestation] + Early neonatal deaths [first week of life]) / (Live births + Late foetal deaths [≥28 weeks]) × 1000
Formula (WHO - for developing countries with less complete records):
PMR = (Late foetal deaths [≥28 weeks] + Postnatal deaths [first week]) / Live births × 1000
ICD-10 Criteria for inclusion:
  • Birth weight ≥ 1000 g (equivalent to ≥28 weeks gestation)
  • If birth weight unavailable: gestation ≥ 28 weeks
  • If both unavailable: crown-to-heel length ≥ 35 cm
Example: In a hospital with 10,000 deliveries in a year: 80 stillbirths (≥28 weeks) + 60 early neonatal deaths = 140 perinatal deaths:
PMR = (140 / [10,000 + 80]) × 1000 = 13.9 per 1000
Key point: PMR is a sensitive indicator of the quality of obstetric and neonatal care. International comparisons are complicated by differences in definitions between the WHO formula and that of industrialised nations.

6. Under-5 Mortality Rate (U5MR)

Definition (UNICEF): "The annual number of deaths of children aged under 5 years, expressed as a rate per 1000 live births." More specifically, it measures the probability of dying between birth and exactly 5 years of age.
Formula:
U5MR = (Deaths of children < 5 years of age in a given year / Live births in the same year) × 1000
Example: If a country records 2,000,000 live births and 60,000 deaths in children under 5:
U5MR = (60,000 / 2,000,000) × 1000 = 30 per 1000 live births
Key points:
  • UNICEF considers it the best single indicator of social development and well-being - more informative than GNP per capita, because it reflects income, nutrition, healthcare, and basic education
  • Global progress: U5MR fell from 93 per 1000 (1990) to 39 per 1000 (2018) - a 58% reduction
  • Sub-Saharan Africa has the highest U5MR: 78 per 1000 (2018)
  • High-income countries: 1 in 185 children dies before age 5; Sub-Saharan Africa: 1 in 13

Quick Comparison Summary

IndicatorNumeratorDenominatorMultiplier
CDRAll deaths in a yearMid-year population× 1000
IMRDeaths < 1 yearLive births× 1000
MMRMaternal deaths (pregnancy/42 days post)Live births× 100,000
NMRDeaths < 28 daysLive births× 1000
PMRStillbirths (≥28 wks) + Early neonatal deaths (≤7 days)Live births (+ stillbirths, in some formulae)× 1000
U5MRDeaths < 5 yearsLive births× 1000
  • Park's Textbook of Preventive and Social Medicine, pp. 656-666 (MCH indicators and mortality rates)
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