Another look at returns to birthweight

Area of Science:

• Perinatal epidemiology
• Developmental pediatrics
• Health economics

Background:

• Birthweight is a key indicator of infant health, but its causal effects are debated.
• Existing research often uses twin or sibling studies, which may not fully account for confounding factors.
• Variation in birthweight in developed nations is largely driven by gestational age, not solely intrauterine growth.

Purpose of the Study:

• To investigate the causal impact of birthweight on infant mortality and long-term health and educational outcomes.
• To address limitations of previous sibling and twin study designs.
• To utilize a novel instrumental variable approach for exogenous variation in gestation length.

Main Methods:

• Employed an instrumental variable (IV) strategy using the diagnosis of placenta previa.
• Placenta previa provides exogenous variation in gestational length, a primary driver of birthweight.
• Departed from traditional twin fixed-effects estimators to mitigate confounding.

Main Results:

• Increased birthweight demonstrates protective effects against infant mortality and health capital loss, including cerebral palsy.
• In contrast to sibling and twin studies, no significant evidence was found for long-run effects on non-health outcomes like test scores.
• The short-run impacts of birthweight on health outcomes have notably diminished over recent decades.

Conclusions:

• Birthweight remains a critical factor for immediate infant survival and health.
• The long-term influence of birthweight on cognitive and educational outcomes appears less pronounced than previously suggested by some studies.
• Public health interventions focusing on birthweight may have diminishing returns for long-term non-health outcomes over time.