摘要：Objectives . This study examined the relationship between timing of insurance coverage and prenatal care among low-income women. Methods . Timeliness of prenatal care initiation and adequacy of number of visits were studied among 5455 low-income participants in a larger cross-sectional statewide survey of postpartum women in California during 1994–1995. Results . Although only 2% of women remained uninsured throughout pregnancy, one fifth lacked coverage during the first trimester. Rates of untimely care were highest (≥64%) among women who were uninsured throughout their pregnancy or whose coverage began after the first trimester; rates were lowest (about 10%) among women who obtained coverage during the first trimester. Women who first obtained Medi-Cal coverage during pregnancy were at low risk of having too few visits. Conclusions . Timing of prenatal coverage should be considered in research on the relationship between coverage and care use among low-income women. Earlier studies that relied solely on principal payer information, without data on when coverage began, may have led to inaccurate inferences about lack of coverage as a barrier to prenatal care. During the 1980s, federal legislation was enacted to markedly expand eligibility for maternity care coverage under the Medicaid program. In 1986, the average Medicaid eligibility income threshold for maternity care was approximately 55% of the federal poverty level 1 ; by 1990, pregnant women with incomes up to 133% of the federal poverty level were eligible for Medicaid coverage in all states, and several states had raised the eligibility cutoff to 185% of the poverty level or higher. 1, 2 In many states, the eligibility expansions also addressed previous obstacles arising from features of the Medicaid system itself through efforts such as placing eligibility workers at prenatal care sites, streamlining application and certification procedures, and making Medicaid participation more attractive to obstetric providers. Policies expanding Medicaid eligibility for maternity care coverage were based on the premise that reducing the number of uninsured pregnant women would lead to improved access to prenatal care. However, several large studies that assessed the impact of expansions in public coverage did not reveal significant improvements in the use of prenatal care despite reductions in the proportions of uninsured pregnant women. 3– 5 In an earlier study using 1990 statewide California birth certificate data (within 2 years of major eligibility expansions in that state), we found elevated rates of untimely care among women with Medi-Cal (California's Medicaid program) as their primary prenatal care payer, even in comparison with uninsured women. 6 Findings from these studies have prompted widespread doubts about the extent to which lack of insurance coverage is a crucial barrier. However, all of the studies relied on secondary data sources that did not include information on the point during pregnancy at which a woman's coverage began. Birth certificate data in several states currently include information on the principal prenatal care payer, defined as the third-party payer that at the time of delivery is expected to have contributed most to a woman's prenatal care expenses, regardless of when the coverage began. Although lack of insurance coverage during the first trimester of pregnancy (as opposed to later coverage status) could logically be viewed as the relevant issue in assessing potential financial barriers to first-trimester initiation of prenatal care, only women who lack third-party coverage throughout their pregnancies are classified as “uninsured” according to principal prenatal payer information. We found 2 earlier studies that examined the relationship between timing of coverage during pregnancy and use of prenatal care. Linking records from birth certificates, hospital discharge abstracts, and Medicaid enrollment files in Washington State before the major expansions in Medicaid eligibility, Katz et al. 7 found that both women who enrolled in Medicaid after their first trimester of pregnancy and those who had Medicaid coverage before pregnancy were at elevated risk of inadequate prenatal care, whereas women who obtained Medicaid coverage during their first trimester were not. The authors controlled for age, marital status, and gravidity but lacked information on factors such as income, education, language, transportation, child care, and women's knowledge and attitudes that might have explained the observed relationships between timing of coverage and use of care. After adjusting for a number of systems and personal characteristics, Gazmararian et al. 8 found (without distinguishing trimester of enrollment) that low-income women who enrolled in a managed care plan in Tennessee during their pregnancy were more likely to initiate care after the first trimester than were women who enrolled before they became pregnant. The present study analyzed data from a statewide survey of access to maternity care conducted in California during 1994–1995, approximately 5 years after eligibility for Medicaid coverage of maternity care was expanded to include women with family incomes up to 200% of the federal poverty level. Our main objective was to describe the relationship between third-party coverage and the use of prenatal care after implementation of the major Medi-Cal eligibility expansions, taking into account both timing of coverage and other important factors that might have influenced women's use of prenatal care. We focused on women with family incomes at or below 200% of the federal poverty level, all of whom were thus eligible for Medi-Cal prenatal care coverage. Findings from an earlier study indicated that inadequate use of prenatal care is rare among women in higher income groups. 9
