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., accounting 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 infections, respiratory problems, and developmental delays (1, 4, 5). These risks drop significantly as gestational age increases (5). 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 (1, 5).

While many babies born preterm have low birthweight, this is not always the case. Some infants are born prematurely at normal weight; others are born full-term at low weight. Infants with a low birthweight (less than 5.5 lbs) have increased risks for numerous chronic health and developmental problems (1). Babies with a very low birthweight (less than 3.3 lbs) face even greater risks of adverse health outcomes (6).

Decades of research have shown large inequities in birth outcomes by race/ethnicity—even after controlling for socioeconomic status—with rates of preterm birth, low birthweight, and infant mortality consistently higher among African American/black populations when compared with other groups (1, 2, 7). Additional factors linked to preterm birth and low birthweight include smoking or substance use, delayed or inadequate prenatal care, short interpregnancy intervals, and experiences of violence, racism, or stress (1, 2, 3, 4). Mothers who live in rural areas or areas with environmental hazards, become pregnant as teenagers or older women, are underweight or overweight during pregnancy, or have existing physical or mental health problems also are at increased risk (1, 2, 3, 4).

The share of infants born at low birthweight in 2022 was the highest on record since 1995 (the first year for which data are available), statewide and nationally. In California, the more than 31,000 infants born weighing less than 2,500 grams (around 5.5 pounds) accounted for 7.3% of all births that year, up from 6.1% in 1995. More than 4,500 of these babies were born at very low birthweight (or 1,500 grams, approximately 3.3lbs)—1.1% of all births, similar to percentages going back to 1995.

Low birthweight is not experienced evenly across local areas and demographic groups. In 2022, the share of infants born at very low birthweight to Butte County mothers (0.6%) was more than twice the rate for mothers in Sonoma County (1.4%). Statewide and nationally, mothers ages 45 and older consistently deliver a higher percentage of low birthweight babies when compared with younger mothers.

Rates of low birthweight are disproportionately high among African American/black populations. In California and the U.S., across years with data, the share of infants born at low birthweight to African American/black mothers is typically around double that for babies born to white mothers—e.g., 12.2% vs. 5.7% for California in 2017.

The percentage of infants born preterm—prior to 37 weeks of gestation, based on obstetric estimates—to California mothers in 2022 was 9.1%, lower than both the national average of 10.4% and the U.S. Department of Health and Human Services’ Healthy People 2030 target of 9.4%. California has met this target since 2008 (the first year for which data are available), while the U.S. rate has remained higher than 9.5% over this period.

Low birthweight and preterm birth are leading causes of infant mortality and major contributors to long-term health conditions (1, 2, 3). In the U.S., reducing maternal and newborn deaths and disabilities has been a public health priority for decades, backed by substantial spending, yet the nation generally fares worse than other wealthy countries (1). It also faces stark, long-standing inequities by race/ethnicity and socioeconomic status, particularly among African American/black populations, who experience disproportionately high rates of negative childbirth outcomes (1, 4). California fares better than the nation as a whole on rates of preterm birth and low birthweight, but has much more work to do in developing innovative solutions and addressing persistent disparities (1, 5, 6).

Risk factors for low birthweight and preterm birth are multi-dimensional, interconnected, and influenced by the environment, institutions, and social practices (1, 5, 7). Policies focused on physical, mental, and behavioral health education, prevention, and treatment can reduce some risk factors by helping women reach good health before pregnancy, avoid smoking and substance use while pregnant, and forgo elective deliveries before 39 weeks of gestation (1, 2, 3). Social issues and inequities underlying this broad network of factors can be targeted through strategies addressing structural determinants of health and systemic barriers to quality health care (1, 4, 5, 7).

Policy, system, and practice options that could influence preterm births and low birthweight include:

• Adopting a comprehensive approach to health in which contraception counseling, reproductive planning (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 are integrated into routine care (1, 3, 4)
• Ensuring that everyone of reproductive age has access to timely, affordable, high-quality preconception care (which provides an opportunity to identify and address key health risks before pregnancy) and prenatal care, including group prenatal care, which provides social support that may be especially helpful for some mothers (1, 2, 4, 5)
• Prioritizing patient-centered, community-informed, and culturally-responsive health settings and services—through increased workforce diversity, training on biases in the health care system, and expanded medical education on social determinants of health—particularly in rural areas and in African American/black and American Indian/Alaska Native communities (4, 5, 7, 8)
• Advancing strategies to reduce smoking among pregnant women, and ensuring that effective tobacco cessation services are available and reimbursed by insurance (1, 2, 5)
• Reducing elective preterm deliveries, along with pregnancies at higher risk for preterm delivery, such as multiples (twins, triplets, etc.) conceived with assisted reproductive therapies (1, 3)
• Promoting cross-sector efforts to address the root causes of disparities in birth outcomes by targeting structural racism, economic and educational inequities, environmental exposures, and other social determinants of health (1, 3, 4, 7, 9)
• Supporting evidence-based, tailored strategies to increase public awareness about reproductive planning, preconception health, and pregnancy risks associated with maternal age, unhealthy weight, substance use, and other physical and mental health issues (1, 2, 3, 4)