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Infant Mortality Rate (IMR) - Park's Textbook of Preventive and Social Medicine

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Definition

IMR = (Number of deaths of children < 1 year of age in a year / Number of live births in the same year) × 1000

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Importance of IMR

1. The most important indicator of health status of a community
2. An indicator of the level of living of people in general
3. A measure of effectiveness of MCH (Maternal & Child Health) services

• (a) Infant mortality is the largest single age-category of mortality
• (b) Deaths at this age are due to a peculiar set of conditions to which adults are less exposed or vulnerable
• (c) Infant mortality is affected quickly and directly by specific health programmes and may change more rapidly than the general death rate

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International Comparisons

• Developed countries: ~4 per 1000 live births
• Least developed countries: ~46 per 1000 live births
• South Asian average: 35 per 1000 live births

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IMR in India

• Kerala has the lowest IMR (7/1000) with the highest female literacy (91.98%) and lowest birth rate
• Madhya Pradesh has the highest IMR (48/1000) with lower female literacy and highest birth rate
• India's current IMR = 32 per 1000 live births (2018)

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Mortality Pattern

• Deaths in 0-1 year account for 10.5% of total deaths in India
• About 71.7% of infant deaths occur within the first month (neonatal period)
• Of neonatal deaths, 54.6% occur in the first week of birth
• Risk is greatest in the first 24-48 hours after birth

• In developed countries: male death rates are higher than female
• In India: after age 1 month (post-neonatal period), female deaths are higher than male - attributed to social factors unfavourable to females in India
• Neonatal death rate is higher for males; post-neonatal death rate is higher for females

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Medical Causes of Infant Mortality (Table 26 - Park's)

• Low birth weight: 57%
• Respiratory infections: 17%
• Congenital malformations: 5%
• Diarrhoeal diseases: 4%
• Birth injury: 3%
• Cord infection: 2%
• Unclassified: 18%

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Factors Affecting Infant Mortality

1. Biological Factors

• Babies < 2.5 kg (LBW) and > 4 kg are at special risk
• Virtually all infants weighing < 1000 g succumb
• Major cause of LBW = poor maternal nutrition

• IMR is greatest when mother is < 19 years or > 30 years
• Very young mothers tend to be poorer and less educated

• Highest mortality: first born and 5th or later children
• Lowest mortality: second born
• Risk escalates after the 3rd birth
• Nutritional deficiency deaths are 3-4 times higher for 5th+ birth order

• IMR highest for infants born after interval of 1 year
• IMR lowest for infants born after interval of 4 years (Khanna Study, India)
• Risk is 2-4 times higher for babies born within 1 year of each other vs those born >2 years apart

• Greater risk due to higher frequency of LBW

• IMR increases with family size
• Diarrhoea, malnutrition, respiratory infections all increase with family size
• Duration of illness also longer in larger families

• High fertility and high infant mortality go together

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2. Economic Factors

• Socio-economic status is the most important variable - both directly and indirectly
• IMR is highest in slums and lowest in richer localities
• Quality of health care and child's environment are closely linked to socio-economic status

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3. Cultural and Social Factors

• Depriving baby of colostrum (first milk)
• Frequent purgation
• Branding the skin
• Application of cowdung to the cut end of umbilical cord
• Faulty feeding practices and early weaning

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Preventive and Social Measures to Reduce IMR

1. Prenatal nutrition - Supplementation of mother's diet; even 500 kcal + 10 g protein extra in last 4 weeks raises birth weight by ~300 g (ICDS programme)
2. Prevention of infection - Immunization (Universal Immunization Programme, 1985); protection against 9 vaccine-preventable diseases
3. Breast-feeding - Most effective measure; safeguard against GI and respiratory infections and PEM
4. Growth monitoring - Low-cost technology to reduce infant mortality
5. Family planning - Limiting family size and spacing births; reduces risk substantially
6. Sanitation - Safe water, proper housing, basic hygiene; risk of dying closely related to the environment
7. Provision of primary health care - Prenatal care to detect high-risk mothers; special care baby units for babies < 2000 g; proper referral services
8. Socio-economic development - Female literacy, nutritional standards, safe water, sanitation, housing, agriculture, industry
9. Education - Especially female education; Tamil Nadu example: mid-day meal programme + improved health care for women reduced IMR from 90 (1984) to 57 (1991) per 1000 live births

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Congenital Malformations - In Detail

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Definitions

• Some are obvious at birth - e.g., cleft palate
• Some become obvious in early life - e.g., congenital dislocation of hip (may escape detection until walking commences)
• Some appear later in life - e.g., patent ductus arteriosus (may be missed until school age)
• Some are inborn errors of metabolism - e.g., PKU, Tay-Sachs disease, galactosaemia, mental retardation

• Major defects - may require surgical intervention (e.g., cleft palate, cardiac defects)
• Minor defects - no functional implications (e.g., skin tags in front of the ear)

• Congenital malformation = structural defects present at birth
• Congenital anomaly = broader term including all biochemical, structural, and functional disorders present at birth

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Incidence

• Congenital anomalies affect approximately 1 in 33 infants
• Result in approximately 3.2 million birth defect-related disabilities every year globally
• An estimated 270,000 newborns die during the first 28 days of life every year from congenital anomalies
• Most common serious congenital disorders: heart defects, neural tube defects, and Down syndrome

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Causes / Aetiology

Frequency of Causes (Robbins Pathology - Table 4.5)

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1. Genetic Factors

• Chromosome either missing or in excess
• Examples:
  • Down's syndrome (Trisomy 21)
  • Klinefelter's syndrome (47, XXY)
  • Turner's syndrome (45, X)
• Most chromosomal disorders arise during gametogenesis and hence are not familial

• Characterized by Mendelian inheritance patterns (autosomal dominant, autosomal recessive, X-linked)
• May affect structural proteins, enzymes, or developmental regulators

• Examples: PKU (phenylketonuria), Tay-Sachs disease, galactosaemia

• Interaction of environmental influences with two or more genes of small effect
• Includes relatively common malformations such as cleft lip and palate and neural tube defects
• Periconceptional folic acid dramatically reduces neural tube defect incidence - demonstrating environmental contribution

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2. Environmental Factors (Teratogens)

(a) Intra-uterine Infections (TORCH + others)

(b) Drugs and Chemicals

(c) Physical Agents

(d) Maternal Diseases

• Diabetes mellitus - Despite advances in antenatal care, diabetic mothers still have higher rates of malformations (cardiac defects, caudal regression syndrome)
• Cardiac failure
• Phenylketonuria (untreated maternal PKU) - causes malformations in offspring

(e) Dietary Factors

• Folic acid deficiency - Neural tube defects; periconceptional folate reduces NTD incidence by up to 70%

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Pathogenesis - Critical Timing Principle

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Risk Factors

• Overall risk of Down's syndrome = 1:800
• Risk for age 40-45 = 1:67

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Common Congenital Malformations

Neural Tube Defects (NTDs)

• Most common CNS malformations
• Two mechanisms:
  1. Failure of neural tube closure (anencephaly, myelomeningocele)
  2. Primary bony defects from abnormal axial mesoderm development (encephalocele, meningocele, spina bifida)
• Folate deficiency in first trimester increases risk
• Folate supplementation in women of childbearing age reduces NTD incidence by up to 70%
• Serum alpha-fetoprotein (AFP) is elevated in NTDs - used for maternal screening

• Spina bifida occulta - Asymptomatic bony defect only
• Spina bifida - Flat, disorganized spinal cord segment with overlying meningeal outpouching
• Myelomeningocele - Extension of CNS tissue through vertebral defect (lumbosacral commonest); causes motor/sensory deficits in lower limbs, bowel and bladder problems
• Anencephaly - Anterior NTD; absence of forebrain and top of skull - incompatible with life
• Encephalocele - Diverticulum of malformed CNS tissue through cranial defect (occipital commonest)

Down's Syndrome (Trisomy 21)

• Most common chromosomal malformation
• Risk sharply increases with maternal age
• Features: intellectual disability, characteristic facies, congenital heart defects

Congenital Heart Defects

• Most common serious congenital anomaly overall
• Causes include chromosomal disorders, single-gene defects, maternal diabetes, rubella, alcohol

Cleft Lip and Palate

• Multifactorial inheritance
• May also be caused by valproic acid, SSRIs, ondansetron, amphetamines, opioids, isotretinoin

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Prenatal Diagnosis

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Prevention of Congenital Malformations

• Advanced maternal age (risk of Down's syndrome)
• Consanguineous marriages

• Drugs: thalidomide, steroid hormones, folate antagonists, anti-convulsants
• Infective agents: rubella (immunization is now routine), CMV, HSV, varicella zoster, Toxoplasma gondii
• Physical agents: X-rays, irradiation, alcohol, pesticides
• Rubella immunization is now routine in many countries
• Folic acid supplementation periconceptionally (reduces NTDs by up to 70%)
• Avoid unnecessary drugs during pregnancy

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SPM Perspective - Congenital Malformations as Reproductive Failure

Sterility → Abortion → Stillbirth → Premature birth → Neonatal death → Congenital malformation → Normal birth
(unfavourable) ←————————————————————————————→ (favourable)

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