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Preventing Low Birthweight (1985) / Chapter Skim
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1. The Significance of Low Birthweight
Pages 21-45

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From page 21...
... , and mortality. In 1930, the Finnish pediatrician, Yllpo, advocated 2,500 -trams as the birthweinht below which infants were at high risk of adverse neonatal outcome, presumably on the basis of inadequate fetal growth.3 This recommendation was formally adopted by the World Health Organization (WHO)
From page 22...
... ~ ° While these gestational age/b~rthwe~ght classif ications proved useful in delineating subpopulations of low birthweight infants with different etiologies and prognoses, they posed some of the same ambiguities as birthweight al one: · Birthweight is a continuous variable and the limit at 2,500 grams does not represent a biologic category, but a singl e point on a continuous curve. The infant born at 2,499 grams does not differ significantly from one born at 2,501 grams on the basis of birthweight alone.
From page 23...
... .~3 l. As with Me 2,500-gram ~ imit, designation of very low birthweight infants as those weighing 1,SOO grams or less reflected convention rather than biologic or iter ia.
From page 24...
... .22 Postneonatal deaths are considered a reflection of environmental factors, particularly infections resulting in diarrhea or respiratory illness.22 2 3 In developing countries, where infant mortality rates remain high, low birthweight accounts for less than half (20 to 40 percent) of postneonatal deaths.2 4
From page 25...
... 59: 624-632, 1982 . Over the first half of the century, infant mortality rates In the United States declined from 100 per 1,000 live births to about 50 per 1,000.25 Most of this decrease occurred among postneonatal deaths, so the majority of observers attribute this decline to changes In the environment, including a reduction in infectious diseases and improved nuts ition.2 2 2 3 2 5 The contr iblltion of shifts in birthweight distribution is unknown, but probably was not significant.
From page 26...
... The two major alternatives in this effort were the prevention of low birthweight in infants and the development of techniques to increase the survivability of low birthweight neonates. The former, which appeared to be more desirable, included efforts to develop early risk assessment programs32 33 and services for high-risk mothers, including those from socioeconom~cally disadvantaged segments of society.3 4 3 5 met ~ ~ ~ - __~ I1le =~:~Vll~l Cal- AL loci ~1-V~: r increasing the survival of low birthweight infants, induced clinicians to develop new management strategies, such as neonatal intensive care units.
From page 27...
... Compared with normal birthweight infants, low birthweight infants are almost 40 times more likely to die in the neonatal per iod; for very low birthweight infants, the relative r isk* of a neonatal death is almost 200 times greater.~9 Not only are low birthweight infants at increased relative r isle of neonatal mortality, but the attributable risk or proportion of all neonatal deaths occurring among low birthweight infants also is high *
From page 28...
... \ 200 Lit * Deaths under 28 days per 1000 live births t Deaths 28 days-11 months per 1000 survivors of neonatal period 100 80 60 40 30 20 10 8 6 4 3 2 \ Neonatal Mortality*
From page 29...
... Thus, in industr Waltzed populations, the proportion of very low birthweight infants is a ma jor predictor of neonatal mortality.4 2 Even controlling for other factors known to affect the risk of neonatal mortality, low birthweight remains the major determinant of neonatal deaths 3 Postneonatal Mortality The relationship between postneonatal mortality and birthweight is not as sharp as that for neonatal mortality; however, low birthweight infants are 5 times more likely than normal birthweight infants to die later in the first year and account for 20 percent of all postneonatal deaths.~9 44 For very low birthweight infants, the relative risk of postneonatal death is 20 times that of normal birthweight infants, and these infants account for between 25 and 30 percent of postneonatal deaths.45 AS suggested by previous reports,23 25 the effect of bi rthweight on postneonatal mortality is modified by socioeconomic factor s. 4 3 Effect of Gestational Age and Other Risk Factors Within birthweight groups, the r isk of mortality is not uniform and var yes with gestational age.
From page 30...
... 9 s ° This finding indicates that the proportion of low birthweight infants ~ argely accounts for the adverse neonatal mortality experiences of these subgroups. Differences in birthweight do not eliminate the increased risk of neonatal death associated with advanced maternal age and prior history of fetal loss.~9 These factors are associated with a combination of increased risk of low birthweight and increased obstetrical vulnerability.
From page 31...
... 12 · Decreases in neonatal mortality for geographically def ined areas have followed the introduction of per inatal intensive care unitS.s`-s6 · Low birthweight infants born in hospitals with intensive care facilities have a higher survival rate than infants born in hospitals without such units,s 7- 5 9 even after controlling for other risk factors known to affect survival.59 This enhanced survival rate persists even in comparisons involving infants transported to regional perinatal care centers shortly after birth.60 6 ~ · Decreases in neonatal mortality in geographically defined regions have been shown to accompany an increase in the proportion of low birthweight and very low birthweight births occurring in tertiary centers. 4 ~ Thus, the current decline In neonatal mortality can be attributed largely to increased survival of high-risk infants.
From page 32...
... As compared with normal birthweight infants, low birthweight infants are twice as likely to have a nontrivial anomaly, and very low birthweight infants are 3 times as likely to have one.7 ~ Among the low birthweight infants, the risk of an anomaly is h igher for those who are small for gestational age than for those whose birthweight is more consistent with the duration of gestation. ~ 0 4 6 Congenital anomalies and neurodevelopmental handicaps are not mutually exclusive occurrences.
From page 33...
... ~ 9 Respiratory Tract Conditions Low birthweight also is a r isk factor for the development of lower respiratory tract conditions . 7 2 Abnormal chest x-rays and pulmonary function and repeated lower respiratory tract infections often have been reported in low birthweight infants who had hyal~ne membrane disease or respiratory distress syndrome as newborns.7 3 - 7 ~ They also may occur in low birthweight infants who were asymptomatic in the neonatal per lad .
From page 34...
... The length of hospital stay in the neonatal period for infants who survive to the first year of life averages 3.5 days for normal birthweight infants, but is much longer for smaller infants: 7 days for those between 2 ,001 and 2, 50 0 grams at bir th; 24 days for those between 1, SO ~ grams and 2 ,000 grams; 57 days for those less than 1,500 grams; 4 5 and 89 days for those less than 1,000 grams.9 ~ The length of stay for nonsurviving infants tends to be much less, although not proportionally less e~ensive.9t 92 Wide variations both in length of stay and direct medical costs per day occur within birthweight groups, depending on the need for ventilation, the presence of congenital anomalies, the need for surgery, and other factors. 9 3 The cost-effectiveness of neonatal intensive care has been questioned.
From page 35...
... Family Function Finally, the birth of a h~gh-risk infant may have major implications for family function. Early attempts to manage low birthweight infants produced an incidental observation of an apparent decrease in attachment between the mother and the surviving low birthweight infant.98 Much recent work suggests that the bonds between mothers and critically ill infants may be disrupted so extensively that inappropriate parenting behaviors emerge.99 ~°° In the extreme, this is seen as overprotectiveness ~ ° ~ ~ o 2 or physical abuse,~° 3 ~ O ~ although the data on the latter may be questioned on methodological grounds.90 More subtle indications of this disruption include altered perceptions and attitudes toward the low birthweight infant, which could have adverse consequences for the chides future development.
From page 36...
... of birthweightrelated conditions to morbidity is quite small. Low birthweight infants are only 1.6 times more likely to have a congenital anomaly, with or without developmental delay, than a normal birthweight infant; they account for 6 percent of infants with these conditions -- about their representation in the population.~9 For very low birthweight infants, the relative risk is only 3.3 times that of normal birthweight infants.~9 For more severe conditions, the relative and attributable risks are smaller.~9 In particular, the proportion of very low birthweight survivors with serious illnesses diminishes rapidly after the first year,8i so the effect of low birthweight infants on morbidity ~ ater in the preschool period is likely to be small.
From page 37...
... 12 Interpretation of these reviews must be cautious, however, because the proportion of children with adverse outcomes has varied significantly among the studies and because selection factors affecting referral to intensive care units might alter the results. More recent data based on clinical series 6 ~ ~ ~ and populationbased morbidity surveys ~ 9 indicate that the increased survival of low birthweight infants has not been associated with an increase in the number with handicaps.
From page 38...
... Although the neonatal mortality rate in the United States has dropped significantly over the past 15 years, this change has not been associated with a comparable decrease in the incidence of low-we~ght births . Instead, the decline has resulted from the increased survival of low birthweight infants, due largely to more specialized, hospital-based management through neonatal intensive care.
From page 39...
... 21. Roops BL, Morgan LJ, and Battaglia FC: Neonatal mortality risk in relation to birth weight and gestational age: Update.
From page 40...
... II . Risk factors reassessed.
From page 41...
... 82:916-920, 1973. Horwood SP, Boyle ME, Torrance GW, and Sinclair JC: Mortality and morbidity of 500- to 1499-gram birthweight infants live-born to residents of a defined geographic region before and after neonatal intensive care.
From page 42...
... and Susser M: Newborn intensive care and neonatal mortality in low-birthweight infants.
From page 43...
... 76e Bryan MH, Hardie MJ, Reilly BJ, and Swyer PR: Pulmonary function studies during the first year of life in infants recovering from the respiratory distress syndrome. Pediatr ics 52 :169-178, 1973.
From page 44...
... 9 5: 755-761, 1979. Phibbs CFS, Williams RL, and Phibbs RH: Newborn risk factors and the costs of neonatal intensive care.
From page 45...
... McCormick MC, Star field BE, and Crawley B: Changes in morbidity associated with decreases in neonatal mortality.


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