Factors affecting nursery survival of very low birth weight infants

The effects of labor on infant mortality among small-for-gestational-age infants in the USA

OBJECTIVE

To determine whether the presence of labor affects infant mortality among small-for-gestational-age (SGA) infants.

METHODS

Data were derived from the United States national linked birth/infant death data sets for 1995-97. Singleton SGA live births in cephalic presentation delivered at 24-42 weeks' gestation were included. Mortality rates for SGA infants exposed and unexposed to labor were compared, and relative risks (RR) were derived using multivariable logistic regression models, after adjusting for potential confounding factors.

RESULTS

Of 986 405 SGA infants, 87.4% were exposed to labor. Infants exposed to labor at 24-31 weeks had greater risks of dying during the early neonatal period (RR 1.79-1.86). Decreased risks of late and postneonatal death were observed at all gestational ages in the presence of labor.

CONCLUSIONS

Exposure to labor is associated with an increased risk of early neonatal death among SGA infants, especially at gestational ages below 32 weeks. Future randomized trials are warranted to determine the optimal obstetric management of these high-risk infants.

Recommendations for repeat courses of antenatal corticosteroids: a decision analysis

OBJECTIVE

The objective was to review the evidence regarding multiple versus single courses of antenatal corticosteroids (ACS), devise dosing regimens based on this evidence, and then, by using decision analysis, compare 5 ACS regimens: (1) single course, (2) weekly courses, (3) every-other-week dosing, (4) every-other-week dosing with no more than 2 courses, and (5) an every-other-week dosing regimen with no third courses after 30 weeks and no second course after 32 weeks.

STUDY DESIGN

The literature was examined for evidence regarding a dose response of the benefits and detriments of ACS. A decision analytic model was designed by using odds ratios, risks of morbidity and mortality, and birth rates from the literature. Mathematic modeling, based on data in the literature, was used to estimate the number of patients who would present at risk for preterm delivery and at what gestational age they would subsequently be delivered. A sensitivity analysis was performed to account for uncertainties in the data.

RESULTS

Of approximately 4 million annual births in the United States, a conservative estimate of 138,000 patients will present between 24 and 34 weeks of gestation at risk for preterm delivery, with 91,915 deliveries. If the 5 different dosing regimens are applied to these patients, strategy 1, the single course of ACS, would result in 30,232 cases of respiratory distress syndrome (RDS) and 4032 neonatal deaths. Three of the other dosing regimens (2, 3, and 5) would all decrease the number of cases of RDS but would concomitantly increase neonatal deaths. Only dosing regimen 4 would decrease the cases of RDS by 2187 without increasing the number of neonatal deaths.

CONCLUSION

There is evidence that there may be a decrease in the incidence of RDS secondary to the use of multiple doses of ACS; however, a concomitant increase in neonatal deaths may also occur. On the basis of our results, we recommend the following: (1) all fetuses between 24 and 34 weeks' gestation at risk for preterm delivery should be given the first course, (2) if there is a persisting risk of preterm delivery subsequent to this, the next course should be given 2 weeks later, and (3) no more than 2 courses should be given. These recommendations need to be examined in a randomized, controlled trial.

Nursery survival for infants of birth weight 500-1500 grams during 1982-1995

OBJECTIVE

To evaluate nursery survival of very low birth weight infants (VLBW) over time, born in the same large inner-city hospital with a predominantly Hispanic population.

METHODS

All liveborn VLBW infants weighing 500-1500 g at birth were included in four time periods of 2 years' duration during 1982 to 1995. Demographics were collected for the obstetric population. Clinical data were collected including maternal and infant perinatal factors. All infants were assigned a cause of death and infants dying with lethal anomalies were then excluded from further evaluations.

RESULTS

Overall survival improved progressively (p = 0.0001) with dramatic improvement in survival of infants 500-750 g birth weight (BW) in period 4 (1994-1995). The number of lethal anomalies did not increase but accounted for a larger portion of deaths in period 4. Decreases in other causes of death over time reflected changes in perinatal care. Although the mothers were high-risk, none of the maternal factors evaluated showed any consistent effect on infant survival. Improved labor and delivery care was associated with improvement in Apgar scores, a decrease in intracranial hemorrhage/intraventricular hemorrhage as a cause of death and an improvement in survival between the first two periods. In spite of the increase in Cesarean sections for infants of 500-750 g BW and their improved survival in period 4, no clear advantage for Cesarean section could be demonstrated. The marked improvement seen in period 4 was associated with three changes in care: increased use of maternal steroids, administration of surfactant, and the use of newer ventilatory methods including high-frequency oscillatory ventilation. Although female gender has been reported to confer a protective influence for survival, this was not found in the final period. Black mothers comprised only about 2.5% of the total obstetric population but delivered approximately 10% of the VLBW infants. Despite the increased incidence of small for gestational age (SGA) among black infants, there were no differences in survival between blacks and Hispanics. Mean birth weight and gestational age in both survivors and nonsurvivors decreased significantly over the four time periods. In period 4, 50% survival occurred at a birth weight of 600-700 g and a gestational age of 23 weeks.

CONCLUSION

Nursery survival improved throughout the period of the study from 1982 to 1995 but especially during period 4 (1994-1995). Improved survival was associated with changes in both maternal and infant care. In infants of BW 500-750 g, gestational age rather than birth weight was more closely associated with survival.

Survival and neonatal morbidity at the limits of viability in the mid 1990s: 22 to 25 weeks

OBJECTIVE

We determined neonatal survival and morbidity rates based on both fetal (stillborn) and neonatal deaths for infants delivered at 22 to 25 weeks' gestation.

STUDY DESIGN

Two hundred seventy-eight deliveries at 22 to 25 weeks' completed gestation were analyzed by gestational age groups between January 1993 and December 1997. Logistic regression models were used to identify maternal and neonatal factors associated with survival.

RESULTS

The rate of fetal death was 24%; 76% of infants were born alive and 46% survived to discharge. Survival rates including fetal death at 22, 23, 24, and 25 weeks were 1.8%, 34%, 49%, and 76%; and survival rates excluding fetal death were 4.6%, 46%, 59%, and 82%, respectively. Logistic regression analyses showed that higher gestational age (P<.0002), higher birth weight (P<.001), female sex (P<.005), and surfactant (P<.003) were associated with neonatal survival. Cesarean section was associated with decreased survival (P <.006).

CONCLUSION

Hospital neonatal survival rates of infants at the limits of viability are significantly lower with the inclusion of fetal deaths. This information should be considered when providing prognostic advice to families when mothers are in labor at 22 to 25 weeks' gestation.

The relationship between Caesarean section and neonatal mortality in very-low-birthweight infants born in Washington State, USA

We examined the associations between Caesarean section and neonatal mortality in singleton liveborn very-low-birthweight (VLBW) infants (500-1499 g) born during 1984-95 in Washington State, USA, using data from the Washington State birth certificate files. The infants included in this study had no life-threatening congenital malformations and had not been delivered by a repeat Caesarean without a trial of labour (n = 5182). For infants weighing 500-749, 750-999, 1000-1249 and 1250-1499 g, the neonatal mortality rates were 57.8%, 18.6%, 9.7% and 4.7%, respectively, and the Caesarean section rates were 28.4%, 47.8%, 48.0% and 44.6%. The adjusted odds ratios (ORs) for neonatal death associated with Caesarean section were 0.55 [95% confidence interval 0.38, 0.78] for the 500-749 g infants (n = 1059), and 1.15 [0.91, 1.45] for the larger (750-1499 g) infants, after adjustment for birth year, type of hospital, birthweight, presence or absence of labour, breech/malpresentation, and other obstetric indications for Caesarean section (prolapsed cord, placenta praevia, eclampsia, pre-eclampsia and chronic hypertension). However, when the larger (750-1499 g) vertex-presenting (n = 3248) and breech/malpresenting (n = 809) infants were considered separately, the adjusted ORs were 1.42 [1.05, 1.91] and 0.37 [0.23, 0.58] respectively. In contrast, among infants weighing 500-749 g, the ORs were not modified by presentation. The results were similar when we restricted analyses to infants without the above obstetric indications for Caesarean section. Because such an observational study is liable to unmeasurable biases and incomplete reporting of obstetric complications, these OR estimates may be subject to residual confounding. In their present state, these recent population-based data support the view that Caesarean sections do not enhance the neonatal survival of larger (> 750 g) VLBW babies when obstetric complications are absent. The possibility of a protective effect of Caesarean section on the survival of breech/malpresenting infants and infants weighing 500-749 g deserves further studies.

Causes of death in the extremely low birth weight infant

OBJECTIVE

To present primary and secondary causes of death confirmed by autopsy for the extremely low birth weight infant.

METHODS

A total of 111 infants weighing between 300 and 1000 g at birth who died and were autopsied at our hospital during the 4-year period 1990-1993 were retrospectively reviewed. Clinical, pathologic, and laboratory data were retrieved including results of placental examinations and autopsy cultures. Primary and secondary causes of death were assigned by the authors.

RESULTS

Infection was the most common primary cause (56/111) followed by respiratory distress syndrome/bronchopulmonary dysplasia (24/111) and congenital defect (15/111). Immaturity as an only cause appeared almost exclusively in infants weighing <500 g at birth. Infection was significantly underdiagnosed clinically with most of these deaths attributed to immaturity or respiratory distress syndrome. In only 1 case was intraventricular hemorrhage considered the primary cause of death although it was present as a secondary cause in 19/111. Infections were divided into congenital (30/56) and acquired (26/56) by time of death. The congenital infections (</=48 hours) consisted of pneumonia and chorioamnionitis/funisitis attributable to maternal enteric organisms. Causative bacteria were obtained in pure culture in a number of these cases. The acquired infections were mainly caused by yeasts and nosocomial bacteria. Sixty-seven percent of the deaths occurred in the first 2 days and 12% were beyond the neonatal period at 29 to 104 days. Care was not initiated or was withdrawn in 50% of the infants, usually within the first 4 hours.

CONCLUSIONS

Infection of the amniotic fluid leading to pneumonia was the major cause of death in the extremely low birth weight infant. Accurate cause of death can not be reliably ascertained without an autopsy accompanied by examination of the placenta in the early deaths. Antibiotic treatment of the mother and infant may have reduced the deaths from infection. Early failure to respond to neonatal intensive care may well indicate presence of a congenital pneumonia.

Delivery of very premature infants: does the caesarean section rate relate to mortality, morbidity, or long-term outcome?

A retrospective analysis of obstetric factors influencing mortality and morbidity of very premature infants (1500 g, less than or equal to 32 weeks' gestation) was undertaken. The study included 275 such infants born in the Department of Obstetrics of the University of Tübingen during the period January 1977 to June 1987. The caesarean section rate of very preterm infants increased from 28% during the period 1977-1982 to 87% during the period 1982-1987 (P less than 0.005), accompanied by an increase in survival rate from 63% to 70%. The improvement in survival rate was statistically significant for the group with birth weight 751-1000 g (P less than 0.01). The overall mortality rate was 31% after caesarean section and 36% after vaginal delivery. Amongst the causes of death of the non-survivors, acidosis was more frequent and amniotic infection syndrome less frequent in the infants delivered vaginally than in those delivered abdominally. The proportion of children with normal development at two years of age was significantly (P less than 0.02) greater amongst those born in 1982-1987 than in those born in 1977-1981. The interpretation of these findings is by no means clear but must include the hypothesis that the increased caesarean section rate may be incidental and in no way related to the improved outcome.