An infant is considered premature if born before the 37th week of pregnancy. Prematurity – being born too early – is the leading cause of death in the first month of life. Being born premature (pre-term) is also a serious health risk for a baby.
Birth weight is the first weight of the newborn measured immediately after birth.
- Low birth weight = less than 5.5 lbs, or 2500 grams.
- Very low birth weight = less than 3.3 lbs, or 1500 grams.
An infant of low birth weight may have been born too small, too early, or both. These conditions often have separate causes, and specific factors may be related to one of these conditions but not the other. For this reason, low birth weight in the Tracking data includes only infants who are born full-term. In the case of very low birth weight infants, however, Tracking includes both pre-term and full-term infants.
- Infant mortality is a death that occurs before 1 year of age.
- Perinatal mortality is death after the 28th week of pregnancy, but before the 7th day of age.
- Neonatal mortality is death of an infant younger than 28 days.
- Postneonatal mortality is death of an infant who is at least 28 days old, but younger than 1 year.
In general terms, the fertility rate relates to the birth rate among women of child-bearing age.
For Tracking, the total fertility rate (TFR) is calculated. The total fertility rate is defined as the sum of the age-specific birth rates of women in five-year age groups multiplied by five. This rate estimates the number of children a cohort of 1,000 women would bear if they all went through their childbearing years having the same age-specific birth rates in effect for a particular time. The age group of women used in Tracking for this calculation is 15 through 44 years.
The sex ratio at birth is the ratio of male to female births. The expected sex ratio at birth (male to female) is 1.05.