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Mortality rates ignore population segment
Letters
Volume 163 Number I, Part I
rate was 7.7% in the "septated" group versus 93% in the "nonseptated" group. Again we thank Drs. Meizner, Levy, and Cohen for their important contribution and accept their conclusion that karyotype determination should be recommended in every case of diagnosed cystic hygromaboth the high-risk (septated) and the relatively low-risk (nonseptated) lesion. Moshe Bronshstein, MD, and Zeev Blumenfeld, MD Department of Obstetrics and Gynecology" A," Rambam Medical Center, Technion-Faculty of Medicine, Haifa, Israel 31096
Mortality rates ignore population segment To the Editors: An article by Resnick et at. (Resnick MB, Carter RL, Ariet M, et at. Effect of birth weight, race, and sex on survival of low-birth-weight infants in neonatal intensive care. AM J OBSTET GYNECOL 1989; 161: 184-7.) reports mortality rates among infants cared for in 10 neonatal intensive care units that constitute the State of Florida's Perinatal Intensive Care Program. These babies were born during a 7-year period. The data presented are very useful, but with one very important caveat. The authors failed to address those babies who were never transferred to the program. As a consequence, their mortality figures are applicable only to programs with referral patterns exactly like theirs. Saigal et at. I illustrate the error introduced when babies born in the community but never transferred to the program are ignored. A total of 66 (12%) of 521 babies with birth weights of 500 to 1000 gm died in community hospitals. None cared for only at community hospitals survived. If these 66 babies had been ignored, mortality rates for the group would have fallen
Table I. Mortality rates by birth weight and gestation Birth weight (gm) <501 501-600 601-700 701-800 801-900 901-1000 Gestational age (wk) <23 23 24 25 26 27 28
No.*
Survival (%)*
9 17 11 16 12 14
0.0 5.9 54.5 56.2 100.0 92.9
15 9 11 15 20 10 16
0.0 ILl 27.3 73.3 80.0 80.0 100.0
*Babies born in hospital July 1987 to December 1988; survival to discharge from hospital.
269
from 53% to 46%. For comparison, mortality figures for live born infants from an inborn population that is approximately 65% black and 80% insured by a third party (private insurance, health maintenance organization, or Medicaid) born during the period July 1987 to December 1988 is provided by birth weight and gestational age in Table I. Provision of data by gestational age is less exact than by birth weight, but is inherently more useful to the obstetrician, and perhaps is as accurate with modern obstetric practice as is prenatal estimate of weight. Although the point estimates of survival rates by birth weight are useful, the utility could be enhanced by the 95% confidence limits of survival rates. Variation by year or by hospital could be used to determine the variability in the estimate. The clinician could then more accurately convey the uncertainty of survival in these small infants. Kenneth L. Harkavy, MD Division of Neonatology, Columbia Hospital for Women Medical Center, 2425 L St. N.w., Washington, DC 20037
REFERENCE 1. Saigal S, Rosenbaum P, Hattersley B, Milner R. Decreased disability rate among 3-year-old survivors weighing 501 to 1000 grams at birth and born to residents of a geographically defined region from 1981 to 1984 compared with 1977 to 1980. J Pediatr 1989;114:839-46.
Reply To the Editors: We appreciate the opportunity to respond to the three points raised by Dr. Harkavy in his Letter to the Editors. In our sample of > 16,000 neonates who received neonatal intensive care unit care in Florida's 10 Regional Perinatal Intensive Care Centers, we found no significant differences between survival of inborn neonates and that of neonates transferred from other hospitals. Data from the State of Florida indicate that the vast majority of high-risk infants in the 10 catchment areas were transferred to one of our centers for neonatal intensive care unit care. If the severity of illness in the transferred group differed from that of the inborn group, the survival rates should have been different. They were not. Whereas gestational age is widely used by obstetricians as an indicator of prematurity, it is quite inexact for infants of extremely low birth weight « 1000 gm). It is hoped that research with ultrasonography in the coming decade will provide a more accurate method to evaluate the degree of prematurity. When we analyzed our data by both race and sex, the 95% confidence level was a maximum of ± 2% for neonates with birth weights of > 1000 gm, ± 4% for those who weighed 600 to 100 gm, and ± 6% for those who weighed <600 gm. A table listing the SE for mortality in each of the 20 birth weight categories by race
Volume 163 Number I, Part I
rate was 7.7% in the "septated" group versus 93% in the "nonseptated" group. Again we thank Drs. Meizner, Levy, and Cohen for their important contribution and accept their conclusion that karyotype determination should be recommended in every case of diagnosed cystic hygromaboth the high-risk (septated) and the relatively low-risk (nonseptated) lesion. Moshe Bronshstein, MD, and Zeev Blumenfeld, MD Department of Obstetrics and Gynecology" A," Rambam Medical Center, Technion-Faculty of Medicine, Haifa, Israel 31096
Mortality rates ignore population segment To the Editors: An article by Resnick et at. (Resnick MB, Carter RL, Ariet M, et at. Effect of birth weight, race, and sex on survival of low-birth-weight infants in neonatal intensive care. AM J OBSTET GYNECOL 1989; 161: 184-7.) reports mortality rates among infants cared for in 10 neonatal intensive care units that constitute the State of Florida's Perinatal Intensive Care Program. These babies were born during a 7-year period. The data presented are very useful, but with one very important caveat. The authors failed to address those babies who were never transferred to the program. As a consequence, their mortality figures are applicable only to programs with referral patterns exactly like theirs. Saigal et at. I illustrate the error introduced when babies born in the community but never transferred to the program are ignored. A total of 66 (12%) of 521 babies with birth weights of 500 to 1000 gm died in community hospitals. None cared for only at community hospitals survived. If these 66 babies had been ignored, mortality rates for the group would have fallen
Table I. Mortality rates by birth weight and gestation Birth weight (gm) <501 501-600 601-700 701-800 801-900 901-1000 Gestational age (wk) <23 23 24 25 26 27 28
No.*
Survival (%)*
9 17 11 16 12 14
0.0 5.9 54.5 56.2 100.0 92.9
15 9 11 15 20 10 16
0.0 ILl 27.3 73.3 80.0 80.0 100.0
*Babies born in hospital July 1987 to December 1988; survival to discharge from hospital.
269
from 53% to 46%. For comparison, mortality figures for live born infants from an inborn population that is approximately 65% black and 80% insured by a third party (private insurance, health maintenance organization, or Medicaid) born during the period July 1987 to December 1988 is provided by birth weight and gestational age in Table I. Provision of data by gestational age is less exact than by birth weight, but is inherently more useful to the obstetrician, and perhaps is as accurate with modern obstetric practice as is prenatal estimate of weight. Although the point estimates of survival rates by birth weight are useful, the utility could be enhanced by the 95% confidence limits of survival rates. Variation by year or by hospital could be used to determine the variability in the estimate. The clinician could then more accurately convey the uncertainty of survival in these small infants. Kenneth L. Harkavy, MD Division of Neonatology, Columbia Hospital for Women Medical Center, 2425 L St. N.w., Washington, DC 20037
REFERENCE 1. Saigal S, Rosenbaum P, Hattersley B, Milner R. Decreased disability rate among 3-year-old survivors weighing 501 to 1000 grams at birth and born to residents of a geographically defined region from 1981 to 1984 compared with 1977 to 1980. J Pediatr 1989;114:839-46.
Reply To the Editors: We appreciate the opportunity to respond to the three points raised by Dr. Harkavy in his Letter to the Editors. In our sample of > 16,000 neonates who received neonatal intensive care unit care in Florida's 10 Regional Perinatal Intensive Care Centers, we found no significant differences between survival of inborn neonates and that of neonates transferred from other hospitals. Data from the State of Florida indicate that the vast majority of high-risk infants in the 10 catchment areas were transferred to one of our centers for neonatal intensive care unit care. If the severity of illness in the transferred group differed from that of the inborn group, the survival rates should have been different. They were not. Whereas gestational age is widely used by obstetricians as an indicator of prematurity, it is quite inexact for infants of extremely low birth weight « 1000 gm). It is hoped that research with ultrasonography in the coming decade will provide a more accurate method to evaluate the degree of prematurity. When we analyzed our data by both race and sex, the 95% confidence level was a maximum of ± 2% for neonates with birth weights of > 1000 gm, ± 4% for those who weighed 600 to 100 gm, and ± 6% for those who weighed <600 gm. A table listing the SE for mortality in each of the 20 birth weight categories by race