PRETERM BIRTHS

This indicator reports the percentage of total annual births which are preterm. Preterm birth is defined as the delivery of an infant at less than 37 weeks of gestation, the period of time between conception and birth. Late preterm births (occurring between 34 to 36 weeks of gestation) moderate preterm births (occurring between 32 to 33 weeks of gestation) and very preterm births (occurring less than 32 weeks of gestation) are subsets of preterm births. Since 2014, preterm births have been calculated by establishing the gestational age based on the obstetric estimate. For years 2013 and earlier, the gestational age was calculated in the month prenatal care began by recording the date of the last normal menses. This change may lead to a slight discontinuity in prenatal care results between years 2013 and 2014.

Preterm birth is an important public health issue requiring sustained focus on its causes, consequences and prevention strategies.1 Several factors – economic, personal, medical and behavioral – may increase the likelihood that a woman has preterm labor and delivers early.2 Compared to infants born at term, preterm infants are more likely to suffer lifelong neurologic, cognitive and behavioral problems.3,4 Preterm births and low birth weight are often, but not always, associated. The preterm birth rate increased slightly from 2016, to 9.9% in 2017, as did the rate of low birthweight (8.3% in 2017).5

Preterm births cost the U.S. health care system more than $26 billion each year.6

• Preterm births accounted for 7.5% of the 38,173 births to Orange County residents in 2017. This percentage is a decrease of 6.3% from 2016 and a decrease of 21% from 2008 (9.5%). By comparison, the rate for the United States was higher at 9.9% as was the rate for California (8.7%).

• Disparities persist with preterm births among Black infants at 10.0%, followed by Hispanic (8.4%), Asian (6.6%) and White (6.5%) infants. The percentages decreased for all races and ethnicities, compared to 2008.

• Out of all preterm births, the percentage of preterm births was lowest among women less than 15 years old (0.1%) and highest among women 30 to 34 years old (31.8%).

• Women 40 years and older have the highest percentage of late preterm births (7.9%).7

Note: Percent calculated from number of births with known obstetric estimate gestational age less than 37 weeks for 2014. Rates prior to 2014 were calculated from last menstrual cycle dates. Source: Orange County Health Care Agency; March of Dimes Report Card

Note: Percent calculated from number of births with known obstetric estimate gestational age less than 37 weeks for 2014. Rates prior to 2014 were calculated from last menstrual cycle dates. Source:

Note: *Percentages based on less than five preterm births (17-36 weeks) are unstable and therefore should be interpreted with caution. Source: Orange County Health Care Agency, Family Health Division