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California Environmental Health Tracking Program

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Last Edited: 9/30/2010

Prematurity and Growth Retardation

Prematurity and growth retardation are commonly used measures of maternal and infant health.  Prematurity occurs when a baby is born too early.  Growth retardation occurs when a fetus grows insufficiently while in the womb.  Both conditions are preventable to varying degrees, and both conditions have been found to be influenced by environmental hazards.


What are prematurity and growth retardation?

Prematurity is when an infant is born early.  Preterm birth rate is a measure of prematurity.  Infants are considered preterm when they are born before completing 37 weeks (about 8.5 months) of pregnancy.

Growth retardation is when an infant fails to grow sufficiently during pregnancy.  This measurement is slightly more complicated than that for prematurity.  Infants are considered to have low birthweight if they weigh less than 2,500 grams (about 5.5 pounds) at birth.  Most low birthweight infants are small because they were born preterm and did not have enough time to finish growing before birth.  Therefore, infants classified as “preterm” and infants classified as “low birthweight” are often the same newborns.  Frequently, however, we wish to consider infants with low birthweight born at full term, which is sometimes called “small-for-gestational age”. 

One way to look at growth retardation is to count the number of full term infants that have low birthweights in spite of being full term.  This means that the baby had enough time in utero, but was still small when born.  An infant that weighs less than 2,500 grams but has completed 37 or more weeks of pregnancy is considered to have term low birthweight. 


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What are the health consequences of prematurity and growth retardation?

Infants that are born preterm or with a low birthweight are at higher risk of dying in the first year of life and of having developmental problems throughout life.1-6 Overall, approximately one-third of all infant deaths in the US are associated with prematurity.7


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What causes prematurity and growth retardation?

Many factors can influence prematurity and fetal growth.  Numerically, most of the infants born with low birthweight are ones that are delivered preterm. Established factors related to prematurity and growth retardation include:

  • Maternal smoking
  • Nutritional status
  • Medical care
  • Levels of stress and/or social support

Scientists are now learning that exposure to pollution during pregnancy can also have an effect on prematurity and growth impairment.8-23 Preterm birth may occur spontaneously or may be medically induced in the situation of impending fetal or maternal compromise.  Rates of preterm birth are therefore partly influenced by obstetrical practice patterns, although fetal and maternal distress and spontaneous preterm birth may have common sources. 24, 25


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