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Preterm infants of normal birth weight (born before 37 completed weeks of gestation and weighing more than 2,250 g) experience a neonatal mortality risk almost four times higher than do term infants in the same weight range. In an analysis of the effect of hospital level of birth on neonatal mortality, such preterm normal weight infants were found to experience higher mortality if born outside of a Level 3 (tertiary care) center. For all singleton infants in this weight-gestation category born in New York City maternity services during a 3-year period (N = 23,257), the relative mortality risk for Level 1 births (compared with Level 3) was 1.72 (P less than .01) and for Level 2 births 1.47 (P less than .05). The excess mortality at Level 1 and Level 2 units was almost entirely due to a more than twofold higher death rate in black infants born in these units. Several potentially confounding socioeconomic, demographic, and biologic variables entered into a logistic regression model could not account for the higher mortality rates for black infants born in Level 1 and Level 2 units. Among black infants born at Level 1 units, deaths in preterm normal birth weight infants were less likely to occur in a receiving tertiary care center than were either deaths in low birth weight infants or deaths in term normal weight infants, suggesting that the need for special care of preterm normal birth weight infants is underestimated in some hospitals without newborn intensive care units.

In a single year in New York City, we identified 1413 neonates who were transferred for medical care from their hospitals of birth; 83% of transferred infants were sent from Level 1 hospitals (no special facilities for sick infants) to Level 3 hospitals (newborn intensive care units). Level 2 hospitals (those with an intermediate level of care) participated little in the transfer process as either senders or receivers. Infants weighing more than 2250 g were rarely transferred. Among low-birth-weight infants born at Level 1 hospitals, the major determinants of transfer were birth weight, gestational age, and Apgar score. Peak transfer rates were for infants weighing 1000-1750 g (84% transferred), those with gestational ages of 28-31 weeks (79% transferred), and those with Apgar scores of 4-6 (68% transferred). Infants with values either above or below these modes were transferred less frequently. Transfer from Level 2 hospitals was also significantly related to birth weight and Apgar score. Socioeconomic indicators such as race, maternal education, ward/private status, and financial coverage for the delivery had no effect on transfer rates. Transferred low-birth-weight infants were a highly selected sample of low-birth-weight infants. Infants transferred from Level 1 hospitals were those in better condition (higher Apgar scores) when weighing less than 1750 g, and those in worse condition (lower Apgar scores) when weighing more than 1750 g.

In an analysis of all singleton births and neonatal deaths with known birth weights and gestational ages in New York City maternity services during a three-year period (1976 to 1978), intensive care services at the hospital of birth were found to influence mortality only in preterm (less than 37 weeks' gestation) or low-birth-weight infants (less than 2251 g). By contrast, for infants who were born at term and of normal birth weight, mortality rates did not differ by level of perinatal care available at the hospital of birth. On the average, preterm and low-birth-weight infants were at a 24% higher risk of death if birth occurred outside of a level 3 center, regardless of whether birth occurred at a level 1 or level 2 hospital. Preterm and low-birth-weight infants, though constituting only 12% of births, accounted for 70% of neonatal deaths in New York City. The remaining infants, ie, those born at term and of normal birth weight, who experienced no measurable mortality advantage when born in a level 3 hospital, accounted for 88% of all births.

To maintain a stable over-all prevalence of handicap, the rate of handicap among survivors must decline in parallel to the decline in mortality among live births. The 24 per cent decline in mortality among low-birthweight infants in New York City between 1962 and 1976 requires a 35 to 39 per cent decline in the rate of neurological impairment among low-birthweight survivors simply to avoid the production of an increased number of handicapped children in the population as a whole. Such evidence as we have suggests that the declining morbidity may not be keeping pace with the recent declines in mortality: thus, although more healthy survivors will result from newborn intensive care, a modest increase in the prevalence of handicap may also ensue.

In New York City, newborn units classified as level 1 (no intensive care) frequently transfer low-birth-weight infants to units classified as level 3 (complete intensive care), but level 2 units (those with intermediate levels of care) transfer rarely. As deaths occurring in the first hours of life are unlikely to be affected by infant transport services, early (first four hours), late (four hours to 28 days), and overall neonatal death rates were separately examined at each of the three levels of care for singleton live-births weighing 501 to 2,250 g. As previously reported, overall neonatal mortality (adjusted for birth weight, gestational age, sex, and race) for births at level 1 units (163.0/1,000) and level 2 units (168.1/1,000) was similar, and rates for births at level 3 (128.0/1,000) were significantly lower. Mortality up to four hours, and from four hours to 28 days, however, differed between level 1 and level 2 units. Among early deaths, the mortality for level 1 births was 68.0/1,000, significantly higher than both the rate for level 2 births (46.0/1,000) and for level 3 births (40.6/1,000). Between four hours and 28 days, mortality relative to level 3 improved for level 1 births, but worsened for level 2 births. For infants with birth weight less than 1,251 g, for whom transport rates from level 1 units are highest, mortality in level 1 births was higher than in level 2 births only until 18 hours of life; thereafter, level 2 mortality was higher.(ABSTRACT TRUNCATED AT 250 WORDS)

Perinatal mortality has several components which may have distinct epidemiologic features. In an investigation of the total singleton birth population of New York City in 1976-1978 (n = 320,726), the authors divided perinatal mortality into four components: late fetal deaths that occurred before labor (late antepartum fetal deaths), fetal deaths during labor (intrapartum fetal deaths), neonatal deaths, and perinatal deaths attributed to congenital anomalies, and they assessed the relation of each of these to maternal age and parity, controlling for relevant confounding factors. In analyses which controlled for prior fetal loss, type of service (public vs. private), race, marital status, and mother's educational attainment in a multiple logistic regression model, the authors found that: 1) increasing maternal age was strongly associated with antepartum fetal deaths but not with intrapartum fetal deaths, while older maternal age was also associated with perinatal deaths attributed to congenital anomalies; 2) high parity bore a strong relationship to intrapartum fetal deaths, but none to antepartum fetal deaths, neonatal deaths, or congenital anomaly deaths; and 3) for neonatal death, there was a statistically significant (p less than 0.001) interaction between parity and age such that mothers over 34 years old having their first birth were at especially high risk.

This study examines the utility of birth weight-specific neonatal mortality rates in removing the confounding effects, in comparisons of mortality in low birth weight infants, of several factors that influence crude neonatal mortality. For this purpose, the effects of social, demographic, and biological attributes of mothers on the mortality of their low birth weight babies were examined in the total population of infants weighing 501-2000 gm born in New York City in 1976, 1977, and the first 11 months of 1978 (N = 10,187). The results confirm previous observations that race, sex, and gestational age-for-weight all exert significant influences on mortality even within narrow (250 gm) birth weight bands. However, mothers' education, number of prenatal visits and whether delivery was on private or ward service, all variables which substantially affect crude neonatal mortality, had no overall effect on weight-specific mortality in the weight range under consideration. Two other socioeconomic indicators, whether delivery was financed by Medicaid, and the marital status of the mother, did significantly affect weight-specific mortality, but their effects were abolished when gestation, race, and sex were entered into the analysis. Although neither maternal age nor parity had any significant individual effects on low birth weight mortality, a linear trend towards lower mortality in older mothers was discovered, and certain age-parity combinations experienced significantly elevated or reduced mortality. In general, weight-specific mortality in low birth weight infants is little influenced by the socioeconomic circumstances of their mothers, particularly when race, sex, and gestation are taken into account. Weight-specific neonatal mortality can therefore be a useful tool in the analysis of the effectiveness of perinatal medical care given to low birth weight infants.

We examined the neonatal mortality rates of low-birth-weight infants (501 to 2250 g) born between 1976 and 1978 in three kinds of hospitals in New York City: those with newborn-intensive-care units (Level 3), those with capabilities for the care of most premature infants (Level 2), and those without any special facilities for premature newborns (Level 1). Among 13,560 singleton low-birth-weight infants, the adjusted neonatal mortality rate for Level 3 hospitals was 128.5 per thousand live births - significantly lower (P less than 0.001) than the rates for both level 2 (168.1) and Level 1 units (163.0). The association of level of care with mortality could not be accounted for by differences between groups in social or demographic status, in prenatal care, or in medical complication of pregnancy. We infer that birth at a Level 3 center lowers neonatal mortality in low-birth-weight infants. However, only 34 per cent of the patients in this study were born in such units.

The effect of level of perinatal care on rates of intrapartum fetal death was studied in births of infants weighing greater than 1000 gm in New York City in 1976 to 1978. With potential confounding by birth weight, gestational age, and several other variables controlled, intrapartum fetal death rates decreased as intensiveness of care increased. Compared with births in Level 3 maternity units (perinatal intensive care), births in Level 1 units (community hospitals) had a 61% excess risk of intrapartum fetal death (p less than 0.01) and births in Level 2 units (intermediate level of care) had a 35% excess risk (p = 0.06). The effect of hospital level on intrapartum fetal death rates could not be attributed to differences in the classification of fetal deaths during labor across hospital levels, since no compensatory differences in late antepartum fetal death rates were found. Our findings in a total population are compatible with several studies carried out in single hospitals that have reported declines in intrapartum fetal death rates, especially in births more closely attended during labor. Fetal deaths that occur in labor, as contrasted with fetal deaths occurring before labor, constitute a perinatal outcome that is especially sensitive to level of obstetric care.