Explaining the 2001-02 infant mortality increase: data from the linked birth/infant death data set

Area of Science:

• Public Health
• Demography
• Neonatal Research

Background:

• The U.S. infant mortality rate (IMR) saw its first increase in over 40 years, rising from 6.8 to 7.0 deaths per 1,000 live births between 2001 and 2002.
• Increases in IMR were observed for very low birthweight, preterm, and very preterm infants.

Purpose of the Study:

• To analyze the contributing factors to the increase in U.S. infant mortality between 2001 and 2002.
• To investigate the role of changes in birthweight distribution, specifically the rise in births weighing less than 750 grams.

Main Methods:

• Analysis of U.S. birth and death records from 2001-2002.
• Examination of birthweight distribution shifts and their impact on overall infant mortality.
• Evaluation of hypotheses related to reporting changes, risk profiles, and medical management.

Main Results:

• The primary driver of the increased IMR was a shift in birthweight distribution, with a notable rise in infants born weighing less than 750 grams.
• Increased births of infants under 750 grams occurred across non-Hispanic white, non-Hispanic black, and Hispanic women, and among mothers aged 20-34.
• While multiple births contributed, the majority of the increase in very low birthweight infants occurred among singletons.

Conclusions:

• The increase in infant mortality is significantly linked to a rise in births of extremely low birthweight infants (<750g).
• Factors contributing to the increase in <750g births include demographic shifts and potentially changes in medical practices, though further research is needed.
• The complex interplay of factors necessitates more detailed studies to fully understand and address the 2001-2002 infant mortality increase.