Prenatal care and pregnancy outcome in an HMO and general population: a multivariate cohort analysis.

Abstract

The use of prenatal care and pregnancy outcome was studied in 4148 deliveries among members of a well-established health maintenance organization (HMO) and 19,116 births among the 1973-1974 White birth cohort in the Portland, Oregon [USA] area. Mothers in the HMO were almost 1 yr older on the average, slightly better educated and less frequently unmarried, but had virtually identical past pregnancy histories when compared with the general population cohort. HMO members began prenatal care 1 mo. later and had 3 fewer visits than the general population (P < 0.01); 78% of the general population and only 64% of HMO members began prenatal care in the 1st trimester (P < 0.01). With maternal risk held constant, low birthweight, neonatal mortality and infant mortality were 1.5-5 times greater with late, less frequent prenatal care than with early, frequent care. Multivariate analysis demonstrated a positive relationship between prenatal care and birthweight. Although this relationship was independent of risk factors recorded on birth certificates, it is not necessarily a causal relationship. Unadjusted prematurity, neonatal and infant mortality rates did not differ between the HMO and general populations. Multivariate analyses indicated that, independent of all maternal risk factors, HMO membership was associated with an increase of 30 g in the predicted birthweight (P < 0.01), but had no effect on mortality. In Portland, pregnancy outcome for HMO members is apparently comparable to that of general population.