Ultrasonographic prediction of neonatal survival in extremely low-birth-weight infants

Perinatal factors affecting survival and survival without disability of extreme premature infants at two years of age

OBJECTIVE

To study obstetrical factors leading to very preterm delivery (between 24 and 28 weeks) and to relate these factors to neonatal outcome and psychomotor development at two years.

STUDY DESIGN

Among 144 infants born alive before 28 weeks of gestation at a single perinatal center between January 1993 and December 1996, we analyzed the influence on neonatal outcome and on psychomotor development at 24 months of a variety of perinatal and neonatal factors. Psychomotor development at two years was classified as: normal, borderline, or moderately or severely handicapped.

RESULTS

During the study period, 114 women delivered live infants before 28 weeks' gestation: 87 singletons, 25 sets of twins, 1 set of triplets and 1 set of quadruplets. All 144 live-born infants received neonatal resuscitation: 50 died before discharge. At two years of age, 6 of the 94 survivors were lost to follow-up. Assessments of the psychomotor development of the other 88 was normal for 52%; borderline for 20%, moderately handicapped for 20%, and severely handicapped for 8%. Multivariate analysis found that two factors affected survival: birthweight and fetal heart rate. (The 42% of infants with a birthweight below 700 g survived versus 83% above 900 g, P<0.001, OR=5.2, 95% CI (confidence interval) [2.4-11.2].)

CONCLUSION

These data show the influence of perinatal factors on the outcome of very preterm infants; birthweight and fetal heart rate are strongly correlated with survival. Gestational age is a good predictor of psychomotor development at two years.

Fetal heart rate and survival of the very premature newborn

OBJECTIVE

Our purpose was to study the likelihood of survival of infants who are born before 28 weeks of gestation and to examine the influence of fetal heart rate findings on neonatal death.

STUDY DESIGN

In this retrospective study, we analyzed the mortality rate of infants at 2 months of age as a function of various obstetric and prenatal indicators.

RESULTS

At 2 months, 207 of 325 children were still alive. The survival rate was also a function of gestational age, birth weight, the administration of corticosteroids, multiple pregnancies, and fetal heart rate. Fetal heart rate had the greatest effect on the mortality rate. Children with a reactive rate were 4 times more likely to survive than children with a flat tracing (P =.003; odd ratio, 4; 95% CI, 12.1; 39.8).

CONCLUSION

The results in our study lead us to think that recording the fetal heart rate before and during labor may be useful in the prediction of perinatal death and may help obstetric decision-making.

Survival of the extremely preterm infant in North America in the 1990s

Survival of extremely premature infants has been significantly higher in the last decade than previously, and may well have improved during this time. The majority of infants greater than or equal to 25 weeks' gestation survive today. Survival of infants 23 and 24 weeks' gestation is significantly lower, but is by no means negligible. Reports of survival of infants less than 23 weeks or less than 500-g birth weight are not unique. Moreover, the maximum survival of infants less than or equal to 25 weeks possible with current state-of-the-art care is not known. Currently available data do not allow survival of the individual extremely low-birth weight or extremely premature infant to be predicted with clinically acceptable accuracy. The concept of a limit of viability is vague and clinically and ethically simplistic. The provision of neonatal intensive care is not necessarily beneficial or justified merely because it affords some minimal chance of survival. This phrase should not be used to summarize the complex issues involved in balancing maternal and neonatal risks and benefits of intrapartum and neonatal care of the extremely low-birth weight or the extremely premature fetus and infant, the suffering of the infant and family, parental values and autonomy, and consumption of limited communal resources. It should be deleted from our vocabulary.

Obstetric determinants of neonatal survival: antenatal predictors of neonatal survival and morbidity in extremely low birth weight infants

OBJECTIVE

The aim of the study was to compare clinical and ultrasonographic variables obtained before delivery as predictors of neonatal survival and morbidity in infants weighing </=1000 g at birth.

STUDY DESIGN

Maternal data available before the birth of singleton infants with birth weights </=1000 g who were delivered at the 11 tertiary perinatal centers of the National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Research Units were studied. Births that followed extramural delivery, antepartum stillbirths, multiple gestations, induced abortions, infants with major malformations, and fetuses delivered at <20 weeks' gestation were excluded. Ultrasonographic variables, including estimated fetal weight, obstetrically estimated gestational age, femur length, and biparietal diameter, and clinical variables, such as maternal race, antenatal care, substance abuse, medical treatment, reason for delivery, fetal gender, and presentation, were studied with logistic regression as predictors of neonatal outcome, including intrapartum stillbirth, neonatal death, and survival to 120 days after birth or to discharge from the hospital with or without the presence of markers of major morbidity.

RESULTS

Eight hundred eight infants met enrollment criteria; 63 were excluded because of incomplete data and 32 were excluded because of malformations, leaving 713 for analysis, 386 of whom had an ultrasonographic examination within 3 days of delivery that recorded femur length, biparietal diameter, and estimated fetal weight. Forty-two percent of births were the result of preterm labor, 22% were the result of preterm ruptured membranes, 12% were the result of preeclampsia or eclampsia, 9% were the result of fetal distress, 4% were the result of placenta previa or abruptio placentae, and 2% were the result of intrauterine growth restriction. Perinatal mortality before 24 weeks' gestation exceeded 81% (19% stillbirths and 62% neonatal deaths) but declined sharply thereafter. Most survivors born before 26 weeks' gestation had serious morbidity. Fetal femur length and estimated gestational age predicted survival better than did biparietal diameter or estimated fetal weight. Infants who survived with markers of serious long-term morbidity could not be distinguished from those who survived without morbidity markers before delivery by ultrasonography or clinical data. Threshold values for ultrasonographic measurements of biparietal diameter and femur length were developed to distinguish fetuses with no chance of survival.

CONCLUSION

Ultrasonographic assessment of either fetal femur length or gestational age predicts neonatal mortality better than do other antenatal tests. No tests accurately predicted neonatal morbidity in infants weighing </=1000 g at birth.

Prenatal prediction of neonatal outcome in the extremely low-birth-weight infant

OBJECTIVE

Our goal was to identify prenatally available parameters that correlate with neonatal outcome and could be used for predicting such outcome in the extremely low-birth-weight pregnancy.

STUDY DESIGN

From 1990 through 1995, obstetric and neonatal data of live-born nonanomalous singleton infants with birth weights between 400 and 1000 gm were reviewed. Only cases in which ultrasonographic biometry, including biparietal diameter, abdominal circumference, and femur length, was performed < or =3 days before delivery were included. Overall survival (defined as alive at discharge) and survival without specific severe neonatal morbidities (namely, retinopathy of prematurity [stage 3 or 4], intraventricular hemorrhage [grade 3 or 4], periventricular leukomalacia, chronic lung disease, and deafness) were ascertained. The best combination of prenatal parameters for the prediction of overall survival and survival without severe morbidity was determined by backward stepwise logistic regression analyses.

RESULTS

The most significant prenatal predictors of overall survival were the obstetric estimate of gestational age and the abdominal circumference (chi2 = 11.8036, p = 0.0006 and chi2 = 8.1862, p < 0.005, respectively). Survival without severe morbidity was also predicted by the same combination of parameters (chi2 = 21.9079, p = 0.0001 and chi2 = 6.538, p = 0.01, respectively). The estimated fetal weight was not a significant independent predictor of either category of outcome (chi2 = 0.1249, p = 0.72 and chi2 = 0.0361, p = 0.85, respectively). On the basis of the regression formulas, curves displaying the probabilities of overall survival and survival without severe morbidity with any combination of gestational age and abdominal circumference were developed.

CONCLUSION

The combination of gestational age and the abdominal circumference measurements appears to be superior to any combination that included estimated fetal weight data for predicting neonatal outcome in the neonates weighing < or =1000 gm. We developed a mechanism for predicting neonatal outcome in this weight category on the basis of prenatally available parameters. This information could prove useful for both parental counseling and obstetric decision making.

Accuracy of estimated fetal weight below 1,000 g

The Warsof formula is 1 of 3 currently recommended by the Australian Society for Ultrasound in Medicine for the routine estimation of fetal weight. However, this formula was derived using mostly large fetuses, and its accuracy in extremely low birth-weight fetuses is not known. Using this formula, we studied 184 infants delivering within 14 days of an estimated fetal weight (EFW) < 1,000 g. The mean percent error in EFW was 11.7% underestimation, with 80% of infants underestimated and 61% of estimates within 15% error. The percent error was consistent at 9.6% throughout the first 9 days, but increased to 32% after 10 days post scan (p < 0.0001). There was a significant association between the accuracy of EFW and maternal height, but not with placental position, liquor volume or multiple pregnancy. EFW underestimated birth-weight on average by 9.6% during the first week, and this error appeared to be mainly due to the formula. The error in EFW became unacceptable after 9 days and repeating the estimate before 10 days is recommended. A different formula may be more suitable for extremely low birth-weight fetuses.