Improvements in neonatal care have increased survival rates for very low birth weight infants

Recent changes in neonatal care--in particular, the use of antenatal steroids, cesarean delivery, steroids to treat chronic lung disease and surfactant to treat respiratory distress syndrome--appear to have contributed to the survival of very low birth weight babies. In 1989-1990, four-fifths of infants weighing 1,500 g or less at birth survived until being discharged from the hospital; the survival rates of infants weighing 601-700 g at birth and those born at 24-26 weeks' gestation improved markedly over rates for 1987-1988. These are among the principal findings of an analysis of data from the National Institute for Child Health and Human Development (NICHD) Neonatal Research Network.(1)

The seven centers that participate in the network registry,* which was established to survey neonatal care and outcomes, as well as to collect social, demographic, pregnancy, delivery and outcome data pertaining to infants weighing 501-1,500 g at birth who were either born at the centers or admitted there for neonatal care. The study investigators compared outcome data for the 1,804 infants born at the centers between November 1989 and October 1990 with data for those born in 1987-1988, the network's first year.

On average, the mothers of the infants born in 1989-1990 were about 25 years old; 22% were teenagers. Most of the women were single (71%). The majority (64%) were black; whites, Hispanics and women of other races constituted 29%, 6% and 1%, respectively, of the mothers. For 26% of the mothers, this was the first pregnancy, and for 38%, it was the first delivery. Some 18% of the women had received no prenatal care.

The infants, who were about evenly distributed between males and females, had a mean birth weight of 1,059 g; among the research centers, the mean birth weight ranged from 1,028 g to 1,138 g. When calculated on the basis of standard obstetric measures, mean gestational age was about 28 weeks, and roughly two-fifths of the infants were born at 27 weeks' gestation or earlier; postnatal assessment based on physical criteria yielded a slightly later gestational age distribution. Some 23% of the infants were judged to be small for their gestational age.

Overall, 78% of the infants born in 1989-1990 survived until their discharge home or to a long-term care facility. As in 1987-1988, the survival rate rose with birth weight, from 39% of those weighing less than 750 g at birth to 77% of those weighing 751-1,000 g and more than 90% of those at higher birth weights. Moreover, a trend toward increased survival was apparent among infants weighing 900 g or less at birth: The survival rate was 20% for infants weighing 501-600 g at birth, 41% for those weighing 601-700 g, 65% for those weighing 701-800 g and 76% for those weighing 801-900 g. These rates are 11-37% higher than those for infants born two years earlier--18% for birth weight 501-600 g, 30% for 601-700 g, 56% for 701-800 g and 65% for 801-900 g. The greatest change was for babies weighing 601-700 g at birth.

Survival also increased with gestational age. Among the 1,743 infants born in 1989-1990 for whom gestational age was determined by obstetric measures, he survival rate was 15-18% for those born at or before 23 weeks' gestation, 54% for those born at 24 weeks,59% for those at 25 weeks and 71% for those at 26 weeks. By comparison, in the earlier period, these figures ranged from 13% to 59%. The largest improvements in mean survival rates occurred among those born at 24-26 weeks' gestation. (Because assessments based on physical criteria overestimate gestational age, survival rates based on these assessments are lower at each gestational age.)

Approximately one-fifth of women were given antenatal steroids, and two-thirds of these received a full course. One-half of the infants were delivered by cesarean section; for those weighing 750 g or less, the proportion was slightly more than one-third. About three-quarters of infants weighing 1,000 g or less, one-half of those weighing 1,001-1,250 g and one-third of those weighing more than 1,250 g required intubation in the delivery room. As indicated by Apgar scores, the majority of infants born before 26 weeks' gestation needed resuscitation and ventilation.

Respiratory distress syndrome and respiratory insufficiency affected 56% of the very low birth weight infants overall and 76-82% of those born at 27 weeks' gestation or earlier. Surfactant therapy was administered to 45% of affected infants, and to 23% of very low birth weight babies overall. (The centers in the NICHD network began using surfactant therapy to treat respiratory problems in late 1989.)

Infants weighing 1,000 g or less at birth commonly received prolonged oxygen and ventilator therapy, and the proportion receiving such treatment was inversely associated with birth weight: Among infants surviving to 28 days, 70-80% of those who weighed 750 g or less at birth received oxygen or ventilator therapy, compared with only 2-5% of those who weighed more than 1,250 g at birth.

Similarly, the prevalence of chronic lung disease, which affected 11% of the surviving very low birth weight infants, was inversely related to birth weight, declining from 35% among the smallest infants to 3% among the largest. Some 28% of very low birth weight infants who required oxygen for 28 days or more (6% of all those who survived to 28 days) received steroid therapy to treat chronic lung disease.

On average, surviving very low birth weight infants remained hospitalized for 62 days; the average among those who did not survive was 18 days. Despite increased survival, infants' length of stay did not increase between 1987-1988 and 1989-1990. Length of stay decreased as gestational age increased, from about 119 days for those born at 23 weeks or earlier to 73 days for those born at 26-28 weeks' gestation.

Most surviving very low birth weight infants (78%) did not experience major neonatal complications that have adverse effects on later development, such as chronic lung disease, necrotizing enterocolitis (a condition associated with intestinal immaturity), intracranial hemorrhage and lesions around the ventricles of the brain. The proportion of infants without these complications rose from about one-fifth of those weighing 750 g or less at birth to four-fifths of those whose birth weight was more than 1,000 g. Like survival overall, survival without major morbidity increased between 1987-1988 and 1989-1990 in each birthweight category examined.

According to the analysts, changes in neonatal care between 1987-1988 and 1989-1990--the increasing use of antenatal steroids and cesarean section, the introduction of steroids o treat chronic lung disease and the use of surfactant therapy--may account for much of the improvement in survival their study revealed. Furthermore, they consider it reassuring that the incidence of serious complications is not increasing, despite the higher survival rates; nevertheless, they caution, greater use must be made of effective treatments (such as antenatal steroids), and additional research is needed in the prevention and treatment of major types of morbidity.

* The participating centers were Rainbow Babies and Children's Hospital at Case Western Reserve University, the University of Alabama, the University of Miami, the University of Tennessee at Memphis, the University of Texas Southwestern Medical Center at Dallas, and the University of Vermont and Dartmouth Hitchcock Medical Center (which combined as one collaborating center).

Reference

1. M. Hack et al., "Very-Low-Birth-Weight Outcomes of the National Institute of Child Health and Human Development Neonatal Network, November 1989 to October 1990," American Journal of Obstetrics and Gynecology, 172:457-464, 1995.

Copyright The Alan Guttmacher Institute Jul 1995
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