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

Clinical monitoring of late fetal growth restriction

Late fetal growth restriction (FGR) poses its own challenges in respect of diagnosis, surveillance and delivery timing. Perinatal morbidity is relatively rare, and mortality extremely unusual, but given that late FGR is much more frequent than early FGR, the burden on neonatal services must not be underestimated. Doppler findings are more subtle than in early FGR, and growth rate rather than absolute fetal size may be important in defining the condition. Though umbilical artery Doppler changes form the basis for triggering delivery: reversed end diastolic flow at 32 weeks, absent at 34 weeks and raised PI at 36 weeks, other modalities of monitoring - for example cardiotocography and cerebral Doppler - are important in surveillance and timing follow up of the condition.

Biochemical tests of placental function versus ultrasound assessment of fetal size for stillbirth and small-for-gestational-age infants

BACKGROUND

Stillbirth affects 2.6 million pregnancies worldwide each year. Whilst the majority of cases occur in low- and middle-income countries, stillbirth remains an important clinical issue for high-income countries (HICs) - with both the UK and the USA reporting rates above the mean for HICs. In HICs, the most frequently reported association with stillbirth is placental dysfunction. Placental dysfunction may be evident clinically as fetal growth restriction (FGR) and small-for-dates infants. It can be caused by placental abruption or hypertensive disorders of pregnancy and many other disorders and factorsPlacental abnormalities are noted in 11% to 65% of stillbirths. Identification of FGA is difficult in utero. Small-for-gestational age (SGA), as assessed after birth, is the most commonly used surrogate measure for this outcome. The degree of SGA is associated with the likelihood of FGR; 30% of infants with a birthweight < 10th centile are thought to be FGR, while 70% of infants with a birthweight < 3rd centile are thought to be FGR. Critically, SGA is the most significant antenatal risk factor for a stillborn infant. Correct identification of SGA infants is associated with a reduction in the perinatal mortality rate. However, currently used tests, such as measurement of symphysis-fundal height, have a low reported sensitivity and specificity for the identification of SGA infants.

OBJECTIVES

The primary objective was to assess and compare the diagnostic accuracy of ultrasound assessment of fetal growth by estimated fetal weight (EFW) and placental biomarkers alone and in any combination used after 24 weeks of pregnancy in the identification of placental dysfunction as evidenced by either stillbirth, or birth of a SGA infant. Secondary objectives were to investigate the effect of clinical and methodological factors on test performance.

SEARCH METHODS

We developed full search strategies with no language or date restrictions. The following sources were searched: MEDLINE, MEDLINE In Process and Embase via Ovid, Cochrane (Wiley) CENTRAL, Science Citation Index (Web of Science), CINAHL (EBSCO) with search strategies adapted for each database as required; ISRCTN Registry, UK Clinical Trials Gateway, WHO International Clinical Trials Portal and ClinicalTrials.gov for ongoing studies; specialist abstract and conference proceeding resources (British Library's ZETOC and Web of Science Conference Proceedings Citation Index). Search last conducted in Ocober 2016.

SELECTION CRITERIA

We included studies of pregnant women of any age with a gestation of at least 24 weeks if relevant outcomes of pregnancy (live birth/stillbirth; SGA infant) were assessed. Studies were included irrespective of whether pregnant women were deemed to be low or high risk for complications or were of mixed populations (low and high risk). Pregnancies complicated by fetal abnormalities and multi-fetal pregnancies were excluded as they have a higher risk of stillbirth from non-placental causes. With regard to biochemical tests, we included assays performed using any technique and at any threshold used to determine test positivity.

DATA COLLECTION AND ANALYSIS

We extracted the numbers of true positive, false positive, false negative, and true negative test results from each study. We assessed risk of bias and applicability using the QUADAS-2 tool. Meta-analyses were performed using the hierarchical summary ROC model to estimate and compare test accuracy.

MAIN RESULTS

We included 91 studies that evaluated seven tests - blood tests for human placental lactogen (hPL), oestriol, placental growth factor (PlGF) and uric acid, ultrasound EFW and placental grading and urinary oestriol - in a total of 175,426 pregnant women, in which 15,471 pregnancies ended in the birth of a small baby and 740 pregnancies which ended in stillbirth. The quality of included studies was variable with most domains at low risk of bias although 59% of studies were deemed to be of unclear risk of bias for the reference standard domain. Fifty-three per cent of studies were of high concern for applicability due to inclusion of only high- or low-risk women.Using all available data for SGA (86 studies; 159,490 pregnancies involving 15,471 SGA infants), there was evidence of a difference in accuracy (P < 0.0001) between the seven tests for detecting pregnancies that are SGA at birth. Ultrasound EFW was the most accurate test for detecting SGA at birth with a diagnostic odds ratio (DOR) of 21.3 (95% CI 13.1 to 34.6); hPL was the most accurate biochemical test with a DOR of 4.78 (95% CI 3.21 to 7.13). In a hypothetical cohort of 1000 pregnant women, at the median specificity of 0.88 and median prevalence of 19%, EFW, hPL, oestriol, urinary oestriol, uric acid, PlGF and placental grading will miss 50 (95% CI 32 to 68), 116 (97 to 133), 124 (108 to 137), 127 (95 to 152), 139 (118 to 154), 144 (118 to 161), and 144 (122 to 161) SGA infants, respectively. For the detection of pregnancies ending in stillbirth (21 studies; 100,687 pregnancies involving 740 stillbirths), in an indirect comparison of the four biochemical tests, PlGF was the most accurate test with a DOR of 49.2 (95% CI 12.7 to 191). In a hypothetical cohort of 1000 pregnant women, at the median specificity of 0.78 and median prevalence of 1.7%, PlGF, hPL, urinary oestriol and uric acid will miss 2 (95% CI 0 to 4), 4 (2 to 8), 6 (6 to 7) and 8 (3 to 13) stillbirths, respectively. No studies assessed the accuracy of ultrasound EFW for detection of pregnancy ending in stillbirth.

AUTHORS' CONCLUSIONS

Biochemical markers of placental dysfunction used alone have insufficient accuracy to identify pregnancies ending in SGA or stillbirth. Studies combining U and placental biomarkers are needed to determine whether this approach improves diagnostic accuracy over the use of ultrasound estimation of fetal size or biochemical markers of placental dysfunction used alone. Many of the studies included in this review were carried out between 1974 and 2016. Studies of placental substances were mostly carried out before 1991 and after 2013; earlier studies may not reflect developments in test technology.

Nationwide Birth Weight and Gestational Age-specific Neonatal Mortality Rate in Taiwan

BACKGROUND

There are limited nationwide data relating to neonatal mortality rate in Taiwan. This study aims to provide updated national birth weight/gestational age-specific neonatal mortality reference rates.

METHODS

We abstracted the birth registration database from the Ministry of Interior in Taiwan from 1998 to 2002 and linked the data to the death registration database from the Ministry of Health and Welfare in Taiwan between 1998 and 2003. We included 1,331,785 infants born between 20 weeks and 44 weeks of gestation and weighing within the median ± 2 interquartile ranges in their age group in this study. We calculated the birth weight/gestational age-specific neonatal mortality rates of different genders by birth weight increments of 250 g and at gestational age intervals of 1 week. A Poisson regression model was used in modeling the mortality data.

RESULTS

A total of 4,169 deaths occurred within 28 days of life out of a total of 1,331,785 live births between 20 weeks and 44 weeks of gestation, giving a neonatal mortality rate (0-27 days) of 3.39 per 1000 live births for males and 2.80 per 1000 for females. The infant mortality rate remained higher in the male (5.91 per 1000) than the female (5.10 per 1000) population within the 1(st) year of life. Birth weight/gestational age-specific neonatal mortality rates were plotted with curves representing the 10(th) and 90(th) birth weight percentiles. The risk of an early neonatal death (0-6 days) does not exceed 50% except for female neonates < 500 g and ≤ 23 weeks, which implies that the limit of viability is now at 23 weeks for females.

CONCLUSION

We have provided an easy-to-use birth weight/gestational age-specific neonatal mortality rate chart as a reference document that physicians and parents can use to make decisions based on ethical considerations relating to whether to give palliative care or further invasive management. The normative data are crucial for public health policies on neonatal care in Taiwan.

Fetal growth: a review of terms, concepts and issues relevant to obstetrics

The perinatal literature includes several potentially confusing and controversial terms and concepts related to fetal size and growth. This article discusses fetal growth from an obstetric perspective and addresses various issues including the physiologic mechanisms that determine fetal growth trajectories, known risk factors for abnormal fetal growth, diagnostic and prognostic issues related to restricted and excessive growth and temporal trends in fetal growth. Also addressed are distinctions between fetal growth 'standards' and fetal growth 'references', and between fetal growth charts based on estimated fetal weight vs those based on birth weight. Other concepts discussed include the incidence of fetal growth restriction in pregnancy (does the frequency of fetal growth restriction increase or decrease with increasing gestation?), the obstetric implications of studies showing associations between fetal growth and adult chronic illnesses (such as coronary heart disease) and the need for customizing fetal growth standards.

A population-based study of 518 very preterm neonates from high-risk pregnancies: Prognostic value of umbilical and cerebral artery Doppler velocimetry for mortality before discharge and severe neurological morbidity

OBJECTIVE

To evaluate in everyday practice the predictiveness of fetal umbilical artery and cerebral artery Doppler examination for mortality before discharge and for severe neurological morbidity among very preterm neonates from high-risk pregnancies.

METHODS

Data came from a population-based study (EPIPAGE) of all births before 33 weeks' gestation during 1 year in nine French regions. We examined the prognostic value of Doppler findings among the liveborn singletons delivered after pregnancies with maternal hypertension or antenatal suspicion of small-for-gestational-age status.

RESULTS

This study included 518 fetuses. Predischarge mortality for infants with abnormal umbilical artery Doppler findings was not significantly higher than for those with normal findings. Mortality for infants with abnormal cerebral artery Doppler findings was significantly higher in the bivariate analysis (crude OR: 3.5 (1.6-7.4)). After adjustment, the association between mortality and abnormal cerebral artery Doppler findings remained significant in the subgroup with an abnormal umbilical artery Doppler assessment (OR: 5.1 (1.1-23)). There was no significant association between neurological morbidity and Doppler findings.

CONCLUSION

The prognostic value of Doppler examinations appears lower in this study than in previous hospital series. This suggests the need for quality control and improvements in these examinations.

Survival and major neonatal complications in infants born between 22 0/7 and 24 6/7 weeks of gestation (1999-2003)

OBJECTIVE

This study was undertaken to compare survival and morbidity until discharge in infants born after 22-23 versus 24 weeks' gestational age (GA).

STUDY DESIGN

Cohort study of all infants 25 weeks or less, born in 3 tertiary perinatal centers (1999-2003).

RESULTS

Of a total of 336 infants, 133 (40%) died before or immediately after birth without the provision of life support, 203 (60%) received active neonatal treatment. Infants with life support (n = 82 at 22 to 23 weeks, n = 121 at 24 weeks) differed with respect to antenatal steroid prophylaxis (44% vs 62%) and cesarean section rate (51% vs 71%). Survival was 67% compared with 82% (P = .016). The incidence of intraventricular hemorrhage III or greater or periventricular leukomalacia (15/15%), severe retinopathy of prematurity (18/15%), and chronic lung disease (40/47%) was similar in both GA groups.

CONCLUSIONS

The provision of life support for extremely preterm infants increases their chance of survival without more neonatal morbidity.

Morbidity and mortality of infants born at the threshold of viability: ten years' experience in a single neonatal intensive care unit, 1991-2000

BACKGROUND

The purpose of the present paper was to evaluate the mortality and morbidity of infants born at 22-24 weeks gestation.

METHODS

A total of 78 infants born at 22-24 weeks gestation, who were admitted between January 1991 through December 2000, were retrospectively studied.

RESULTS

Seventy-one of 78 infants were enrolled in the present study. One year survival rates at 22, 23 and 24 weeks were 40.0% (2/5), 61.1% (11/18), and 50.0% (24/48), respectively. Failure of response to surfactant and air leak were associated with death in infants born at 23 weeks gestation. Low Apgar score, intraventricular hemorrhage (> or =III), and sepsis were correlated with death in infants born at 24 weeks gestation. The handicap rates of survivors born at 22, 23, and 24 weeks gestation were 100, 36.4, and 26.1%, respectively.

CONCLUSIONS

The present study indicates that infants born at 22 weeks gestation, in whom pulmonary structure is established, that is, a viable lung that can exchange gas with exogenous surfactant, have a chance to survive, but neurological outcome is still poor. Every possible effort should be made to extend gestation beyond 22 weeks.

Ethical dilemmas in the care of the most premature infants: the waters are murkier than ever

PURPOSE OF REVIEW

Summarize the literature relevant to ethical issues surrounding decisions to provide intensive care to extremely premature newborns.

RECENT FINDINGS

A Texas Supreme Court decision and a position paper are noteworthy for health professionals participating in management decisions with families at risk for extremely preterm delivery.

SUMMARY

In Miller v HCA, the Millers sued the Hospital Corporation of America for resuscitating their approximately 23-week gestation daughter against their wishes. The baby survived with severe neurodevelopmental disabilities. They were awarded $59.9 million in a jury trial. However, the judgment was reversed by the court of appeals, which ruled that parents have no right to withhold urgently needed life-sustaining medical treatment from children with non-terminal impairments, deformities, or disabilities, regardless of their severity. The Supreme Court of Texas upheld that ruling, but reasoned that parents have no right to refuse resuscitation of extremely premature infants prior to birth because they cannot be fully evaluated until birth; therefore, decisions before birth could not be fully informed. Robertson (Hasting Center Report 2004) supports precluding parental refusal of resuscitation before birth. He argues that parents have a right to withhold or withdraw medical treatment from a non-terminally ill child, but only if the child will lack capacity for symbolic interaction. Such severe limitation of quality of life concerns in decision making for extremely premature newborns is inconsistent with current published guidelines, the positions of noted bioethicists, and the practice of many neonatologists. Further, the additional information attained by initiating intensive care in the most premature infants does not justify doing so without parental consent.

Changes in mortality and morbidities among infants born at less than 25 weeks during the post-surfactant era

OBJECTIVES

To compare mortality and death or major morbidity (DOMM) among infants <25 weeks estimated gestational age (EGA) born during two post-surfactant era time periods.

STUDY DESIGN AND PATIENTS

Comparative cohort study of very low birthweight (501-1500 g) infants <25 weeks EGA in the NICHD Neonatal Research Network born during two post-surfactant era time periods (group I, 1991-1994, n=1408; group II, 1995-1998, n=1348). Perinatal and neonatal factors were compared, and group related mortality and DOMM risk were evaluated.

RESULTS

Mortality was higher for group I (63.1% v 56.7%; p=0.0006). Antenatal steroids (ANS) and antenatal antibiotics (AABX), surfactant (p<0.0001), and bronchopulmonary dysplasia (p=0.0008) were more prevalent in group II. In a regression model that controlled for basic and delivery factors only, mortality risk was greater for group I than for group II (odds ratio (OR) 1.4, 95% confidence interval (CI) 1.2 to 1.7); the addition of AABX and surfactant, or ANS (OR 0.97, 95% CI 0.79 to 1.2) to the model appeared to account for this difference. There was no difference in DOMM (86.8% v 88.4%; p=0.2), but risk was lower for group I in regression models that included ANS (OR 0.70, 95% CI 0.52 to 0.94).

CONCLUSION

Survival to discharge was more likely during the more recent period because of group differences in ANS, AABX, and surfactant. However, this treatment shift may reflect an overall more aggressive management approach. More consistent application of treatment has led to improving survival of <25 week EGA infants during the post-surfactant era, but possibly at the cost of greater risk of major in-hospital morbidities.

Ethical considerations in the management of infants born at extremely low gestational age

With ongoing improvements in technology and the understanding of neonatal physiology, there has been increasing debate regarding the gestational age and birth weight limits of an infants' capability of sustaining life outside the womb and how this is to be determined. The objective of this review was to address this issue with an analysis of current data (following the introduction of surfactant therapy in 1990) from published studies of survival in extremely low gestational age infants. We found that survival was possible at 22 completed weeks of gestation but only in < 4% of live births reported. Survival increased from 21% at 23 weeks gestational age to 46% at 24 weeks gestational age. Historically, despite continual advances in neonatology, the mortality at 22 weeks has not improved over the past three decades. Combining the data from studies on survival with evidence from developmental biology, we believe that it is not worthwhile to pursue aggressive support of infants born at < 23 weeks gestational age. Given the complicated issues related to morbidity and mortality in infants born at 22 to 25 weeks gestational age and the ethical implications of the available evidence, we propose the need for a consensus derived framework to help in decision-making.

Management decisions in extremely premature infants

Survival rates in excess of 25% at 23 weeks' gestation and in excess of 50% at 24 weeks' gestation have been reported among live births in the 1990s within tertiary perinatal care centres in the USA and Australia. Decisions about medical management at these gestational ages can no longer be based merely on whether survival is possible. Relevant moral considerations include the primacy of the newborn's best interests, parental autonomy, physicians' duties of beneficence and non-maleficence, and distributive justice. There is significant variability between developed nations in the survival of extremely premature infants among cohorts born within perinatal tertiary care centres. This is, at least to some degree, the result of differences in the aggressiveness of obstetrical and neonatal management at these gestational ages. There is also great variability in the prevalence of major neurodevelopmental disability among survivors. Moreover, the prevalence of major disabilities does not inform quality-of-life considerations adequately. Despite similar gestational age ranges over which the benefit:burden ratio of aggressive obstetric and neonatal care is questioned in developed countries, there is marked variation in the frequency with which it is provided within these ranges. This is understandable given the relevant moral values and the different ways in which competing values will be balanced by different individuals, cultures and societies; the increasing survival of extremely premature infants, but the persistence of high (but widely variable) prevalences of major disabilities reported among survivors and even higher prevalences of mild-to-moderate neurodevelopmental sequelae; our imperfect ability to estimate an individual extremely premature infant's prognosis; and the complexities of estimating the quality of life from the individual's own perspective.

Outcomes for high risk New Zealand newborn infants in 1998-1999: a population based, national study

OBJECTIVE

To determine short term morbidity and mortality outcomes, provision of care, and treatments for a national cohort of high risk infants born in 1998-1999 and admitted to New Zealand neonatal intensive care units (NICUs).

SETTING

All level III (six) and level II (13) NICUs in New Zealand.

METHODS

Prospective audit by the Australian and New Zealand Neonatal Network (ANZNN) of all infants defined as "high risk" (born at < 32 weeks gestation or < 1500 g birth weight, or received assisted ventilation for four hours or more, or had major surgery). Data were collected from birth until discharge home or death.

RESULTS

There were 3368 high risk infants (3.0% of all live births), comprising 1241 (37%) < 32 weeks gestation, 1084 (32%) < 1500 g, 3156 (94%) who received assisted ventilation, and 243 (7%) who received major surgery (categories overlap). Most infants (87%) received some care in tertiary hospitals, and 13% were cared for entirely in non-tertiary hospitals. Survival was 91% for infants < 32 weeks gestation, 97% for infants > or = 32 weeks gestation who received assisted ventilation, and 92% for infants > or = 32 weeks gestation who had major surgery. The proportion of very preterm infants who survived free of early major morbidity was 11%, 28%, 53%, 81%, and 90% for infants born at < 24, 24-25, 26-27, 28-29, and 30-31 weeks gestation respectively.

CONCLUSIONS

These unique population based national data provide contemporary information on the care and early morbidity and mortality outcomes for all high risk infants, whether cared for in hospitals with level III or level II NICUs.

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.

The outcome of extreme prematurity

Significant advances in perinatology and neonatology in the last decade have resulted in increased survival of extremely premature infants. Survival rates for infants born in tertiary perinatal and neonatal care centers in the United States in the 1990s increase with each week of gestational age from 22 through 26 weeks. Reported survival rates at 22 weeks range from 0% to 21% in the few reporting studies. Reported survival rates at 23 and 24 weeks range from 5% to 46% and from 40% to 59%, respectively. These may not be the maximum survival rates possible because at these gestational ages information is either insufficient to determine that obstetric and neonatal intensive care strategies to maximize neonatal survival were used or it is specified that such strategies were not used. Reported survival rates at 25 and 26 weeks range from 60% to 82% and from from 75% to 93%, respectively. The literature regarding the prevalence of major neurodevelopmental disabilities among extremely premature survivors in the last 25 years is heteogeneous, and the reported prevalances of major disability vary much more than do survival rates. However, the majority of extremely premature infants who survive will be free of major disability. Overall, approximately one fifth to one quarter of survivors have at least one major disability-impaired mental development, cerebral palsy, blindness, or deafness. Impaired mental development is the most prevalent disability (17%-21% [95% CI] of survivors affected), followed by cerebral palsy (12%-15% of survivors affected). Blindness and deafness are less common (5% to 8% and 3% to 5% of survivors affected, respectively). Approximately one half of disabled survivors have more than one major disability. Based on studies of infants less than 750 to 1,000 grams birth weight, it can be anticipated that approximately another half of all extremely premature survivors will have one or more subtle neurodevelopmental disabilities in the school and teenage years. There is little evidence to suggest that long-term neurodevelopmental outcome has changed from the late 1970s to the early 1990s or with increasing survival. Survival of individual extremely premature infants cannot be accurately predicted in the immediate perinatal period. Major disability cannot be accurately predicted for individual survivors during the course in the newborn intensive care unit.

The risk of neonatal death in relation to birth weight and maternal hypertensive disease in infants born at 24-32 weeks

OBJECTIVE

To determine the risk of neonatal death (NND) in relation to birth weight for gestational age and the presence or absence of maternal hypertensive disease in preterm neonates.

DESIGN

Record linkage of maternity data and neonatal mortality data.

SETTING

Scotland, UK.

POPULATION

A group of 6946 live singleton preterm neonates without lethal congenital abnormalities born at 24-32 weeks between 1986 and 1992 inclusive. This group included 1448 cases of maternal hypertensive disease and 850 neonatal deaths.

MAIN OUTCOME MEASURE

Neonatal death.

RESULTS

The median birth weight for each gestational week was estimated from a fitted curve and each birth weight was recalculated as a multiple of the relevant median. The frequency of NND was much higher at lower gestations (73% at 24 weeks down to 2% at 32 weeks). Though the overall frequency of NND was lower in cases with hypertensive disease (8.6% versus 13.2%) this can be attributed to the fact that there were relatively fewer hypertensive cases in the high risk group at 24-27 weeks. In the 5498 cases not associated with maternal hypertensive disease, there were 726 NNDs. The mean MoM of birthweight for these NNDs was 0.982 (95% CI 0.967-0.996); this was only marginally different from the population mean (0.998; 95% CI 0.993-1.004). In the 1448 cases with maternal hypertensive disease, there were 124 NNDs. The overall birthweight for gestational age in the hypertensive group was substantially less than that of the whole population (mean MoM 0.84; 95% CI 0.83-0.85) and that of the 124 NNDs was still lower (mean MoM 0.75; 95% CI 0.724-0.782). For both hypertensive and non-hypertensive cases, inspection of the data categorised into deciles showed that there was a continuous increase in the frequency of NND throughout the weight range, being lowest for the heaviest babies and highest for those in the lower centiles.

CONCLUSION

(1) There is a relationship between birthweight for gestational age and risk of NND in infants born at 24-32 weeks; (2) this relationship is a continuum throughout the whole range of birthweight, not focused exclusively on a group defined as SGA; (3) provided appropriate birthweight standards are used, there is no extra effect on mortality from maternal hypertensive disease.

Evidence of selection bias in preterm survival studies: a systematic review

OBJECTIVE

To determine by how much selection bias in preterm infant cohort studies results in an overestimate of survival.

DESIGN

Systematic review of studies reporting survival in infants less than 28 weeks of gestation published 1978-1998. Studies were graded according to cohort definition: A, stillbirths and live births; B, live births; C, neonatal unit admissions. Proportions of infants surviving to discharge were calculated for each week of gestation.

RESULTS

Sixty seven studies report data on 55 cohorts (16 grade A, 23 grade B, 16 grade C). Studies that are more selective report significantly higher survival between 23 and 26 weeks of gestation (grade C > grade B > grade A, p < 0.01), exaggerating survival by 100% and 56% at 23 and 24 weeks respectively.

CONCLUSION

To minimise the potential for overestimating survival around the limits of viability, future studies should endeavour to report the outcome of all pregnancies for each week of gestation (terminations, miscarriages, stillbirths, and all live births).

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.