Национальное исследование ближайшего исхода у новорожденных с экстремально низкой массой тела, родившихся в Финляндии в 1996-1997 гг

A National Short-Term Follow-Up Study of Extremely Low Birth Weight Infants Born in Finland in 1996-1997

Viena Tommiska, Kirsti Heinonen, Sami Ikonen, Pentti Kero, Marja-Leena Pokela, Martin Renlund, Martti Virtanen, and Vineta Fellman

From the Hospital for Children and Adolescents, University of Helsinki, Helsinki, Finland; Department of Pediatrics, University of Kuopio, Kuopio, Finland; Department of Pediatrics, University of Tampere, Tampere, Finland; Department of Pediatrics, University of Turku, Turku, Finland; Department of Pediatrics, University of Oulu, Oulu, Finland; the Department of Obstetrics and Gynecology; and the National Research and Development Center for Welfare and Health, Helsinki, Finland

Objectives. The aims of this prospective nationwide investigation were to establish the birth rate, mortality, and morbidity of extremely low birth weight (ELBW) infants in Finland in 1996-1997, and to analyze risk factors associated with poor outcome.

Participants and Methods. The study population included all stillborn and live-born ELBW infants (birth weight: <1000 g; gestational age: at least 22 gestational weeks [GWs]), born in Finland between January 1, 1996 and December 31, 1997. Surviving infants were followed until discharge or to the age corresponding with 40 GWs. National ELBW infant register data with 101 prenatal and postnatal variables were used to calculate the mortality and morbidity rates. A total of 32 variables were included in risk factor analysis. The risk factors for death and intraventricular hemorrhage (IVH) of the live-born infants as well as for retinopathy of prematurity (ROP) and oxygen dependency of the surviving infants were analyzed using logistic regression models.

Results. A total of 529 ELBW infants (.4% of all newborn infants) were born during the 2-year study. The perinatal mortality of ELBW infants was 55% and accounted for 39% of all perinatal deaths. Of all ELBW infants, 34% were stillborn, 21% died on days 0 through 6, and 3% on days 7 though 28. Neonatal mortality was 38% and postneonatal mortality was 2%. Of the infants who were alive at the age of 4 days, 88% survived. In infants surviving >12 hours, the overall incidence of respiratory distress syndrome (RDS) was 76%; of blood culture-positive septicemia, 22%; of IVH grades II through IV, 20%; and of necrotizing enterocolitis (NEC) with bowel perforation, 9%. The rate of IVH grades II through IV and NEC with bowel perforation decreased with increasing gestational age, but the incidence of RDS did not differ significantly between GWs 24 to 29. A total of 5 infants (2%) needed a shunt operation because of posthemorrhagic ventricular dilatation. Two hundred eleven ELBW infants (40% of all and 60% of live-born infants) survived until discharge or to the age corresponding with 40 GWs. The oxygen dependency rate at the age corresponding to 36 GWs was 39%, and 9% had ROP stage III-V. Neurological status was considered completely normal in 74% of the surviving infants. The proportions of infants born at 22 to 23, 24 to 25, 26 to 27, and 28 to 29 GWs with at least one disability (ROP, oxygen dependency, or abnormal neurological status) at the age corresponding to 36 GWs were 100%, 62%, 51%, and 45%, respectively. Birth weight <600 g and gestational age <25 GWs were the independent risks for death and short-term disability. The primary risk factor for IVH grades II through IV was RDS. Low 5-minute Apgar scores predicted poor prognosis, ie, death or IVH, and antenatal steroid treatment to mothers with threatening premature labor seemed to protect infants against these. Some differences were found in the mortality rates between the 5 university hospital districts: neonatal mortality was significantly lower (25% vs 44%) in one university hospital area and notably higher (53% vs 34%) in another area. Furthermore, significant differences were also found in morbidity, ie, oxygen dependency and ROP rates. Differences in perinatal (79% vs 45%) and neonatal (59% vs 32%) mortality rates were found between secondary and tertiary level hospitals.

Conclusion. Our study shows that even with modern perinatal technology and care, intrauterine and early deaths of ELBW infants are common. The outcome of infants born at 22 to 23 GWs was unfavorable, but the prognosis improved rapidly with increasing maturity. The clear regional and hospital level differences detected in survival rates and in short-term outcome of ELBW infants emphasizes that the mortality and morbidity rates should be continuously followed and that differences should be evaluated in perinatal audit procedures. However, before the overall outcome of ELBW infants can be evaluated, the results of long-term follow-up and the effects of a premature birth on the family should be taken into consideration. prematurity, perinatal mortality, neonatal morbidity, extremely low birth weight infants. With the development of antenatal and neonatal intensive care during the last 2 decades, the survival of the extremely low birth weight (ELBW) infant has improved significantly.1-7 In the 1980s, the survival rate of these infants increased, while the incidence of neurological and other major handicaps of especially those infants born at low gestational weeks (GWs), ie, 22 to 27 GWs, remained constant. Thus, the total number of children born extremely immature and surviving with long-term disability increased.8,9 During the 1990s, new advances in care, such as antenatal steroid treatment to mothers with threatening premature labor, surfactant treatment to infants with respiratory distress syndrome (RDS), and new modes of respiratory support, all known to decrease the mortality of ELBW infants, have become widely used in developed countries. From this period, there are scarce data on long-term follow-up. Most studies on ELBW infants are based on neonatal intensive care unit patient material, and, thus, they include only live-born infants who were considered treatable. Although such studies provide a good regional reference, population-based studies including all stillborn and live-born infants are needed for more reliable and generalizable conclusions. In Finland, all 5 university hospitals together with the National Center of Welfare and Health established in 1996 a register for all ELBW infants born in the country to prospectively assess the short- and long-term prognosis of these infants. Using this register, the aims of this investigation were to establish the birth rate, mortality, and short-term outcome in a comprehensive cohort of ELBW infants born during a 2-year period and to analyze the perinatal and neonatal risk factors associated with poor prognosis.

Pediatrics 2001;107 e2