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Birthweight and infant mortality: a longitudinal study of 5914 Brazilian children
Insights
Low birthweight significantly increases infant mortality risk, especially for respiratory infections. Socioeconomic status interacts with birthweight, amplifying mortality risks for wealthier infants, challenging existing reduction estimates.
Area of Science:
- Pediatrics
- Public Health
- Epidemiology
Background:
- Infant mortality remains a critical global health concern.
- Understanding factors influencing infant mortality is crucial for targeted interventions.
- Previous studies often rely on data from developed nations, potentially limiting applicability elsewhere.
Purpose of the Study:
- To investigate the association between birthweight, gestational age, socioeconomic status, and infant mortality in Southern Brazil.
- To determine the relative risks of mortality for specific causes linked to low birthweight.
- To explore the interaction between birthweight and socioeconomic status on infant mortality.
Main Methods:
- Population-based cohort study involving 5914 liveborn infants in Southern Brazil.
- Follow-up of 87.3% of infants for over 12 months.
- Ascertainment of infant deaths (n=215) through case note review and parental interviews.
Main Results:
- A strong inverse relationship was observed between birthweight and both neonatal and postneonatal mortality.
- Preterm infants with adequate weight for gestational age had twice the infant mortality rate (IMR) compared to small-for-dates infants.
- Low birthweight posed a higher relative risk for respiratory infection deaths than for diarrhea deaths, though estimates were imprecise due to small sample sizes.
- A significant interaction between birthweight and socioeconomic status was found: the mortality risk associated with low birthweight was substantially higher among infants from wealthier families.
Conclusions:
- Birthweight is a critical determinant of infant mortality, with significant implications for neonatal and postneonatal periods.
- Gestational age and birthweight interact to influence mortality risk, with preterm infants facing elevated risks.
- Socioeconomic status modifies the impact of low birthweight on mortality, suggesting that interventions must consider socioeconomic context.
- Existing estimates for infant mortality reduction based on birthweight improvements may be overestimated, particularly when extrapolated from developed country data.
Abstract:
In a population-based cohort study in Southern Brazil, 87.3% of 5914 liveborn infants were followed for over 12 months. The 215 infant deaths occurring in this cohort were studied in relation to birthweight, gestational age and socioeconomic status. Causes of death were ascertained through the review of case notes and interviews with the parents. As predicted, there was a strong inverse association between birthweight and neonatal and postneonatal mortality. Preterm infants with an adequate weight for their gestational age, despite being slightly heavier than small-for-dates, showed an IMR which was twice as large as the latter. The relative risk associated with low birthweight for deaths due to respiratory infections was over twice as large as that for diarrhoea deaths, but there were only 25 deaths in each category and the estimates are therefore not very precise. There was an interaction between birthweight and socioeconomic status, with the relative risk of mortality associated with low birthweight being much larger among rich than among poor infants. Estimates of the magnitude of the reduction in infant mortality which would accompany a given improvement in the birthweight distribution, which have been mostly based on data from developed countries, may prove to be overoptimistic.