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The combined effect of birth weight and length of gestation on mortality during the neonatal period was studied, using information obtained from birth and death certificates filed with the New York State Department of Health for births occurring during 1949, 1950, and 1951 in New York State, exclusive of New York City. The study covered 436,254 single live births over 20 weeks gestation for which data on both birth weight and length of gestation were available. Case fatality rates were determined by birth weight and gestation groups for the entire neonatal period and for 3 age intervals during the neonatal period. For the neonatal period as a whole a characteristic pattern is observed. Within each birth weight group 2500 gm. or less, longer gestation increases the chance of survival; within each gestation group 36 weeks or less, a higher birth weight has a similar effect. A typical example is the range in fatality rates for infants weighing 1001 to 1500 grams at birth. Within this birth weight group, the fatality rate ranges from 40 per cent in the gestation group of 36 weeks or over to 75 per cent in the 24 to 27 weeks gestation group. When fatality rates are computed for 3 successive age periods within the neonatal period, the combined effect of birth weight and gestation produces a characteristic pattern of fatality which is found to be most clearly defined during the first day after birth. However, a similar pattern of fatality is found to exist as well in the age periods from 1 through 6 days and for the remainder of the neonatal period.
Schlesinger et al. (Wed,) studied this question.