Kidsdata.org offers the following measures of low birthweight and preterm birth:

• The number and percentage of infants born at low birthweight (weighing less than 2,500 grams or approximately 5 lbs, 8 oz) overall, by mother's age, and by mother's race/ethnicity
• The number and percentage of infants born at very low birthweight (weighing less than 1,500 grams or approximately 3 lbs, 5 oz)
• The number and percentage of infants born preterm (before 37 weeks of gestation), calculated either by last menstrual period (LMP) or obstetric estimate (OE)

Preterm birth and low birthweight are among the leading causes of infant death in the U.S., and they account for billions of dollars spent annually on health care and other services (1, 2, 3). Babies born prematurely (before 37 completed weeks of gestation) face increased risks of wide-ranging health complications and long-term disabilities, including but not limited to developmental delays, cerebral palsy, heart disease, and respiratory, vision, and hearing problems (4, 5). These risks drop significantly as gestational age increases. Health care professionals recommend waiting until 39 to 40 weeks of gestation for delivery, if possible, as critical infant growth and development occur in the final weeks of pregnancy (4, 5).

While many preterm babies are born too small, this is not always the case. For example, some infants are born prematurely but at a normal weight, and some are born full-term but at a low weight (1). Infants with a low birthweight (less than 5.5 lbs) have increased risks of numerous chronic health and developmental problems (2). Babies with a very low birthweight (less than 3.3 lbs) face even greater risks of adverse health outcomes (2).

Decades of research have shown large inequities in birth outcomes by race/ethnicity, even after controlling for income, with rates of preterm birth, low birthweight, and infant mortality consistently higher for the African American/black population than other groups (6). Many other factors also increase the risk of premature birth and low birthweight, such as low socioeconomic status, inadequate prenatal care, short intervals between pregnancies, maternal smoking or substance use issues, and women who: have had previous pregnancy complications; are carrying more than one baby; have certain uterine or cervical abnormalities; are age 40+ or under age 17; or have other health or mental health problems (2, 4, 7, 8, 9).

The percentage of California infants born at low birthweight rose steadily from 6.1% in 1999 to 6.9% in 2005 and has remained fairly stable through 2016. Statewide, the number of infants born at very low birthweight was 5,445 in 2016 and accounted for 1.1% of all births, similar to percentages going back to 1995.

In 2016 and previous years, low birthweight varied across local areas and demographic groups. Among counties with data in 2016, percentages ranged from 5.2% to 7.9% for infants born at low birthweight and from 0.6% to 2% for infants born at very low birthweight. Statewide, women ages 45 and older consistently have the highest percentage of low birthweight babies (18.2% in 2016) when compared with younger mothers, as do African American/black women (11.6% in 2016) in comparison with other racial/ethnic groups.

Based on obstetric estimates (OE) estimates of gestational age, 8.6% of California infants were born preterm in 2016, down from 9.1% in 2008. Across counties with data, percentages of infants born preterm birth ranged from 6.2% to 10.6% in 2016.

Reducing preterm births and low birthweight have been public health priorities for decades, as they are leading causes of infant mortality and major contributors to long-term disabilities (1). While California fares better than the nation as a whole on rates of babies born prematurely or at low weight, more work is needed, particularly in addressing inequities by race/ethnicity, income, and geography (2, 3, 8).

Some risk factors for low birthweight and preterm birth can be influenced by public and institutional policy focused on education, prevention, and treatment. Risk factors can be reduced through many different strategies, such as ensuring that women are in good health before pregnancy, avoid smoking and substance use while pregnant, and forgo elective deliveries before 39 weeks of gestation, along with broader strategies that address social determinants of health and systemic barriers to health care (4, 5, 6).

Policy and program options that could influence preterm births and low birthweight include:

• Supporting strategies to ensure that all women (and men) of reproductive age have access to continuous, affordable, comprehensive, culturally-sensitive health care before conception, during pregnancy, and after childbirth; as good health before conception can improve birth outcomes, ongoing health care provides an opportunity to identify and address key health risks before pregnancy, such as heart disease and unhealthy weight (1, 4, 5)
• As part of a comprehensive approach to women's health, integrating the following into routine care: reproductive planning and contraception counseling (including promotion of pregnancy intervals of at least 18 months), nutrition education, and screening and referrals for mental health, substance abuse, and social service needs (4, 6)
• Expanding access to timely, high-quality prenatal care, including group prenatal care, which can provide useful social support for pregnant women (4, 6)
• Continuing strategies to reduce smoking among pregnant women, and ensuring that effective tobacco cessation services are available and reimbursed by insurance (4, 6)
• Promoting efforts to reduce elective deliveries before 39 weeks of pregnancy, as important infant development occurs in the final weeks of gestation (4, 6)
• Reducing multiple births (twins, triplets, etc.) conceived with assisted reproductive technology (ART), as these births are more likely to be premature (6)
• Promoting use of evidence-based treatment to reduce specific risks of preterm birth, such as progesterone therapy for certain women and use of low-dose aspirin to prevent preeclampsia for women at risk (6, 7)
• Continuing research to further understand and address factors that contribute to preterm birth and low birthweight, including factors behind racial/ethnic disparities (4, 6, 8)
• Supporting effective strategies to increase public awareness about ways to promote healthy pregnancies; such efforts should be tailored to specific audiences and address topics such as reproductive planning, preconception health, folic acid supplementation, healthy weight, substance use, mental health, and other issues (4, 5, 6)