In California, 83.5% of women begin prenatal care in the first trimester, benefiting the health of both mother and baby. Yet, prenatal care has little impact on birth defects—not surprising since most occur within a few weeks of conception, usually before a woman consults her health care provider or even knows she is pregnant.

Women who don't get prenatal care constitute .7% of the population and have a higher birth defects risk. This is probably because late/no prenatal care is associated with other health behaviors (such as smoking) and social/economic characteristics, which may increase risk.

PRETERM BIRTH AND LOW BIRTHWEIGHT

About 9% of California babies are born prematurely, facing numerous challenges as newborns and a high risk of death. Many public health and obstetric interventions have targeted common causes of preterm birth, such as infection and other pregnancy complications. Birth defects, however, are an often-overlooked contributor.

Birth defects are extremely common in children born prematurely—occurring in about 8% of infants born at less than 30 weeks gestation compared to about 2% among full-term births (37 or more weeks). No single condition accounts for the increase—some infants have only a single birth defect while others have multiple problems.

Birth defects are also more common among low birthweight babies (under 2500 grams or about 5 pounds). Those who are both premature and underweight have the highest risk.