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Average Duration of Pregnancy, by Number of Births (per Pregnancy) --- United States, 2005

Expecting more than one baby? Work with your health care provider to minimize the risk of premature birth.

Chart: Average Duration of Pregnancy at Birth, by Plurality, United States, 2005.

Gestation (duration) is the timeframe beginning with the first day of the last normal menstrual period and ending with the day of birth or day of termination of pregnancy. Normal gestation is considered to be between 37 and 41 weeks. Shorter gestation is associated with poorer birth outcomes, long-term morbidity, and higher infant mortality rates. The risk for shorter gestation is greater with multiple births than singleton births. In 2005, the mean gestational age for singletons was 38.7 weeks, compared with 35.2 weeks for twins, 31.9 weeks for triplets, 29.8 weeks for quadruplets, and 27.4 weeks for quintuplets and higher.

DATA SOURCE: National Vital Statistics System. 2005 natality file. Available at


Centers for Disease Control and Prevention. QuickStats: Mean Gestational Age, by Plurality --- United States, 2005. MMWR 2008;57:09(238).

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