Quantifying the adequacy of prenatal care: a comparison of indices.

In spite of the widespread use of prenatal care utilization indices in the scientific literature, little attention has been given to the extent to which these indices are comparable. This investigation contrasts the way five indices classified cases into categories of prenatal care use. From the 1989-1991 South Carolina Public Use data files, single live births to resident mothers were selected for analysis (N = 169,082). Five prenatal care indices were compared: (a) the modified Institute of Medicine (Kessner) index, (b) a variation of the IOM index using the full American College of Obstetrics and Gynecology visit recommendation, (c) an index derived from the recommendations of the U.S. Public Health Service Expert Panel on Prenatal Care, (d) the GINDEX, and (e) the APNCU index. The proportion of cases assigned to prenatal care utilization categories by each index varied markedly, ranging from 33.6% to 58.1% for adequate care, 9.2% to 20.3% for inadequate care, and 7.4% to 22.6% for intensive utilization. The selection of a prenatal care utilization index for research and policy development purposes requires a careful consideration of the intent, criteria for defining adequacy, and coding assumptions of each index. As these indices are conceptually distinct in their measurement approach, they are likely to yield different patterns of prenatal care use in a population and cannot be used interchangeably. Recommendations for their use are provided.