Birthweight by gestational age in preterm babies according to a Gaussian mixture model

Objective   To provide a statistically sound criterion for identifying implausibly large birthweights for gestational age.
Design   Review of ISTAT 1990–1994 national newborn records.
Setting   Italy
Population   Forty-two thousand and twenty-nine single first and second liveborn preterm babies.
Methods   Two-component Gaussian mixture models are used to describe the birthweight distributions stratified by gestational age. Implausibly large babies are identified through model-based probabilistic clustering.
Main outcome measures   Gestational age misclassification and weight-for-gestational age centile curves
Results   Gestational age appears under-estimated by about six weeks in 12.3% of the cases. Large babies are equally present in males and females, but are more frequent in second-borns than in first-borns, even when parity-specific models are fitted.
Conclusions   The approach allows for a quantification of the gestational age under-estimate error and for data correction through model-based clustering. Correct birthweight distributions and growth curves are also provided.     

Congenital anomalies are an independent risk factor for neonatal morbidity and perinatal mortality in preterm birth

OBJECTIVE: To determine whether congenital anomalies are associated with a high rate of neonatal morbidity in preterm birth. STUDY DESIGN: 312 singletons (22-36 wk) with congenital anomalies that were delivered preterm were compared with a random sample of 936 preterm singleton without congenital anomalies. Data was obtained using the computerized birth discharge records. Statistical analysis included univariate and multivariate logistic regression analyses. RESULTS: Three thousand five hundred and seventy-eight (3578) women with preterm births met the inclusion criteria (singleton with prenatal care). The prevalence of congenital anomalies in the study population was 8.7% (312/3578). Gestational age at delivery was significantly lower in the congenital anomaly group compared with the control (32.0+/-3.7 SD vs. 34.4+/-2.7 SD; p<0.001). The following pregnancy complications were higher in the group with congenital anomalies than in those without anomalies: severe pregnancy induced hypertension (PIH), hydramnions, oligohydramnion, intrauterine growth restriction (IUGR), fetal distress, cesarean section, malpresentation and mal position, abruption placenta, meconium stained amniotic fluid, 1 min Apgar score (<2), 5 min Apgar score (<7). Perinatal mortality rates in 28-32 wk and 33-36 wk were significantly higher in the group with congenital anomalies than in the control group. Neonatal morbidity data (necrotizing enterocolitis, respiratory distress syndrome, bronchopulmonary dysplasia, intraventricular hemorrhage, and sepsis) was available for 909 neonates (239 with congenital anomalies and 670 without congenital anomalies). After adjusting for gestational age, the presence of congenital anomalies remained strongly associated with neonatal morbidity (having one or more of the above mentioned conditions) (adjusted OR: 5.3, 95% CI 3.4-9.2). When adjusting for other confounding variables, congenital anomalies were strongly associated with neonatal morbidity (OR: 6.44, 95% CI 3.94-10.51), and perinatal mortality (OR: 3.08, 95% CI 2.04-4.65). In terms of attributable fraction in our population of preterm births, the proportion of neonatal morbidity and the proportion of perinatal mortality attributable to congenital malformation is 32% and 15%, respectively. CONCLUSION: Congenital anomalies in preterm birth are associated with a higher rate of pregnancy complications and are an independent risk factor for neonatal morbidity and perinatal mortality.     

Factors associated with and causes of perinatal mortality in northeastern Tanzania

Objective. To identify factors associated with perinatal mortality in northeastern Tanzania. Design. Prospective cohort study. Setting. Northeastern Tanzania. Population. 872 mothers and their newborns. Methods. Pregnant women were screened for factors possibly associated with perinatal mortality, including preeclampsia, small-for-gestational age, preterm delivery, anemia, and health-seeking behavior. Fetal growth was monitored using ultrasound. Finally, the specific causes of the perinatal deaths were evaluated. Main outcome measure. Perinatal mortality. Results. Forty-six deaths occurred. Key factors associated with perinatal mortality were preterm delivery (adjusted odds ratio (OR) 14.47, 95% confidence interval (CI) 3.23-64.86, p < 0.001), small-for-gestational age (adjusted OR 3.54, 95%CI 1.18-10.61, p = 0.02), and maternal anemia (adjusted OR 10.34, 95%CI 1.89-56.52, p = 0.007). Adherence to the antenatal care program (adjusted OR 0.027, 95%CI 0.003-0.26, p = 0.002) protected against perinatal mortality. The cause of death in 43% of cases was attributed to complications related to labor and specifically to intrapartum asphyxia (30%) and neonatal infection (13%). Among the remaining deaths, 27% (7/26) were attributed to preeclampsia and 23% (6/26) to small-for-gestational age. Of these, 54% (14/26) were preterm. Conclusions. Preeclampsia, small-for-gestational age and preterm delivery were key risk factors and causes of perinatal mortality in this area of Tanzania. Maternal anemia was also strongly associated with perinatal mortality. Furthermore, asphyxia accounted for a large proportion of the perinatal deaths. Interventions should target the prevention and handling of these conditions in order to reduce perinatal mortality.     

Race and ethnic disparities in fetal mortality, preterm birth, and infant mortality in the United States: an overview

Infant mortality, fetal mortality, and preterm birth all represent important health challenges that have shown little recent improvement. The rate of decrease in both fetal and infant mortality has slowed in recent years, with little decrease since 2000 for infant mortality, and no significant decrease from 2003 to 2005 for fetal mortality. The percentage of preterm births increased by 36% from 1984 to 2006, and then decreased by 4% from 2006 to 2008. There are substantial race and ethnic disparities in fetal and infant mortality and preterm birth, with non-Hispanic black women at greatest risk of unfavorable birth outcomes, followed by American Indian and Puerto Rican women. Infant mortality, fetal mortality, and preterm birth are multifactorial and interrelated problems with similarities in etiology, risk factors and disease pathways. Preterm birth prevention is critical to lowering the infant mortality rate, and to reducing race and ethnic disparities in infant mortality.     

Growth retardation, size at birth and perinatal mortality in twin pregnancy

The records of 194 consecutive pairs of twins were reviewed. Univariate and multivariate analyses of relative risks (RR) of perinatal death were performed. Perinatal mortality rate was higher in small-for-gestational-age twins and in fetuses with discordancy in size at birth more than 20% and 25%. The RR of perinatal death for small-for-gestational-age twins was 4.8 (2.74-8.42 95% CI). For intertwin birth-weight percent differences of 20% and 25%, the RR was 5.48 (3.2-9.38 95% CI) and 7.2 (3.87-13.42 95% CI). Population mortality attributable risk in the two populations (10.36% and 14.5%, respectively) demonstrates the importance of the prenatal assessment of the respective size of twins in preventing perinatal death.     

Safety of birth centre care: perinatal mortality over a 10-year period

Objective   To study perinatal mortality in women booked for birth centre care during pregnancy.
Design   Retrospective cohort study.
Setting   In-hospital birth centre and standard maternity care in Stockholm.
Population   Two thousand and five hundred and thirty-four women (3256 pregnancies) admitted to an in-hospital birth centre over 10 years (1989–2000) and 126,818 women (180,380 pregnancies) who gave birth in standard care during the same period and who met the same medical inclusion criteria as in the birth centre. Multiple pregnancies were excluded.
Methods   Data were collected from the Swedish Medical Birth Register. Information on all cases of perinatal death in the birth centre group was retrieved from the medical records.
Main outcome measure   Perinatal mortality.
Results   No statistically significant difference in the overall perinatal mortality rate was observed between the birth centre group and the standard care group (odds ratio [OR] 1.5, 95% CI 0.9–2.4), but infants of primiparas were at greater risk (OR 2.2, 95% CI 1.3–3.9). Infants of multiparas tended to be at lower risk, but this difference was not statistically significant (OR 0.7, 95% CI 0.3–1.9). These figures were adjusted for maternal age and gestation in multiple regression analyses.
Conclusion   Birth centre care may be less safe for infants of first-time mothers.     

Analysis of perinatal mortality at a teaching hospital in Dar es Salaam, Tanzania, 1999-2003

We conducted a retrospective analysis of perinatal mortality at Muhimbili National Hospital (MNH), Dar es Salaam, Tanzania 1999-2003 in order to categorise/classify perinatal deaths as well as to identify key factors in perinatal care that could be improved. Data were retrieved from the MNH obstetric database and causes of early neonatal deaths were traced from the neonatal ward register. The study includes all foetuses weighing =500g. A modified Nordic-Baltic classification was used for classification of perinatal deaths. Over a 5-year period there were 77,815 babies born with a perinatal mortality rate of 124 per 1000 births, 78% of which was labour related stillbirth. The PMR was 913/1000 for singleton births and 723/1000 for multiple births for babies weighing less than 1500 grams and 65/1000 for singleton births and 116/1000 for multiple births for babies weighing 2500 grams or more. Babies weighing less than 1500 grams contributed 26% of PMR, whereas 41% occurred in babies weighing 2500 grams or more. The majority (79%) of neonatal deaths had Apgar score <7 at 5 minutes and the most common causes of neonatal mortality were birth asphyxia (37%) and prematurity (29%). Labour related deaths were more common in multiple pregnancies. The majority of the perinatal deaths should be essentially avoidable through improved quality of intrapartum care. Establishment of perinatal audit at MNH can help identify key actions for improved care.     

Trends in birth asphyxia,obstetric interventions and perinatal mortality among term singletons: a nationwide cohort study

Objective: The objective of the present study is to investigate trends in birth asphyxia and perinatal mortality in the Netherlands over the last decade.

Methods: A nationwide cohort study among women with a term singleton pregnancy. We assessed trends in birth asphyxia in relation to obstetric interventions for fetal distress. Birth asphyxia was defined as a 5-minute Apgar score <?7 (any asphyxia) or 5-minute Apgar score <?4 (severe asphyxia). Perinatal mortality was defined as mortality during delivery or within 7?days after birth. Multivariable analyses were used to adjust for confounding factors.

Results: The prevalence of birth asphyxia was 0.85% and severe asphyxia 0.16%. Between 1999 and 2010 birth asphyxia decreased significantly with approximately 6% (p?=?0.03) and severe asphyxia with 11% (p?=?0.03). There was no significant change in perinatal mortality rate (0.98 per 1000 live births). Simultaneously the referral rate from primary to secondary care during labor increased from 20% to 24% (p?<?0.0001) and the intervention rate for fetal distress from 5.9% to 7.7% (p?<?0.0001).

Conclusion: In the Netherlands, the risk of birth asphyxia among term singletons has slightly decreased over the last decade; without a significant change in perinatal mortality.     

The risks of spontaneous preterm delivery and perinatal mortality in relation to size at birth according to fetal versus neonatal growth standards

OBJECTIVE: The aim of this study was to test the null hypothesis that size at birth relative to fetal or neonatal growth standards is not a significant variable related to the risk of spontaneous preterm delivery. STUDY DESIGN: This was a hospital-based cohort study of consecutive births at a tertiary care perinatal center from January 1, 1985, to December 31, 1996. A total of 37,377 pregnancies met the following inclusion criteria: (1) singleton gestation, (2) 25 to 40 weeks' gestation, and (3) no anomalies. Neonates were divided into 5 birth weight categories according to either fetal (uncorrected for sex) or neonatal (corrected for sex) growth standards, as follows: (1) intrauterine growth restriction, birth weight <3rd percentile; (2) borderline intrauterine growth restriction, birth weight > or = 3rd percentile and <10th percentile; (3) appropriate for gestational age, birth weight from 10th percentile through 90th percentile; (4) borderline large for gestational age, birth weight >90th percentile but < or = 97th percentile, and (5) large for gestational age, birth weight >97th percentile. Logistic regression analysis was used to estimate the independent effect of birth weight category on the risk of preterm delivery after spontaneous onset of labor, with the appropriate-for-gestational-age group serving as a reference. RESULTS: When fetal growth standards were applied, there was a significant increase in the risk of spontaneous preterm delivery when birth weight was outside the appropriate-for-gestational-age range (odds ratios of 2.5, 1.4, 1.2, and 1.9 for intrauterine growth restriction, borderline intrauterine growth restriction, borderline large-for-gestational age, and large-for-gestational-age groups, respectively). In contrast, when neonatal growth standards were applied, the risks of spontaneous preterm delivery in intrauterine growth restriction, borderline intrauterine growth restriction, and large-for-gestational-age groups were significantly lower (odds ratios of 0.5, 0.7, and 0.7 for intrauterine growth restriction, borderline intrauterine growth restriction, and large-for-gestational-age groups, respectively) because of an underestimation in the number of fetuses with abnormal size at birth delivered prematurely. With both fetal and neonatal growth standards there was a 5-to 6-fold greater risk of perinatal death for both preterm and term fetuses with intrauterine growth restriction. CONCLUSION: Fetal growth standards are more appropriate in predicting the impact of birth weight category on the risk of spontaneous preterm delivery than are neonatal growth standards. When fetal standards are applied, the risks of preterm birth in both extreme abnormal birth weight categories (intrauterine growth restriction and large for gestational age) are 2- to 3-fold greater than the risk among appropriate-for-gestational-age infants.     

Recurrence of preterm birth in twin pregnancies in the presence of a prior singleton preterm birth

OBJECTIVE: We examined recurrence of preterm birth in twin pregnancy in the presence of a previous singleton preterm pregnancy, and assessed if these recurrence risks differed for medically indicated and spontaneous preterm birth. METHODS: A retrospective cohort study was designed using the maternally-linked data of women who delivered a first singleton live birth followed by a twin birth in the second pregnancy (n = 2329) in Missouri (1989--97). We examined preterm birth recurrence at <37 in the second twin pregnancy among women with a prior singleton preterm birth. Recurrence risks were based on hazard ratios (HR) and 95% confidence intervals (CI) estimated from Cox proportional hazards models after adjusting for potential confounders. RESULTS: Preterm birth rates in the second twin pregnancy were 69.0% and 49.9% among women who had a previous preterm and term singleton birth, respectively (HR 1.8, 95% CI 1.6-2.1). The preterm birth rate in the second pregnancy was about 95% when the first singleton pregnancy ended at <30 weeks. Women delivering preterm following a medical intervention in the first pregnancy had increased recurrence for both spontaneous (HR 1.4, 95% CI 1.1-2.0) and indicated (HR 2.4, 95% CI 1.8-3.2) preterm birth; similarly among women with a prior spontaneous preterm birth, hazard ratios were 1.8 (95% CI 1.5-2.1) and 1.6 (95% CI 1.3-1.9), for spontaneous and indicated preterm birth in the second twin pregnancy, respectively. CONCLUSIONS: Women with a singleton preterm birth carry increased risk of preterm birth in the subsequent twin pregnancy. A history of a singleton preterm birth has an independent and additive contribution to risk of preterm birth in the subsequent twin gestation.     

Maternal obesity and neonatal mortality according to subtypes of preterm birth

OBJECTIVE: To examine the association between prepregnancy body mass index (BMI) and neonatal mortality while accounting for the timing of delivery and subtypes of preterm birth. METHODS: The study population included 85,375 liveborn singletons of mothers in the Danish National Birth Cohort (1996-2002) who were interviewed during the second trimester. Information about pregnancy outcomes and neonatal deaths (n=230) was obtained from national registers. The association was estimated by Cox regression analyses and results were presented as hazard ratios with 95% confidence intervals (CIs). RESULTS: Compared with infants of mothers who were at a normal weight before pregnancy (BMI of 18.5 or more but less than 25), neonatal mortality was increased in infants of mothers who were overweight (BMI of 25 or more but less than 30) or obese (BMI of 30 or more) (adjusted hazard ratios 1.7, CI 1.2-2.5, and 1.6, CI 1.0-2.4, respectively). For preterm infants (n=3,934, 136 deaths), neonatal mortality in infants born after preterm premature rupture of membranes (PROM) was significantly increased if they were born to an overweight or obese mother (adjusted hazard ratios 3.5, CI 1.4-8.7, and 5.7, CI 2.2-14.8). There were no associations between high BMI and neonatal mortality in infants born after spontaneous preterm birth without preterm PROM or in infants born after induced preterm delivery. CONCLUSION: High maternal weight seems to increase the risk of neonatal mortality, especially in infants born after preterm PROM. Inflammation or infection related to obesity may be part of the causal pathway. LEVEL OF EVIDENCE: II.     

Smoking in pregnancy: the influence on percentile birth weight, mean birth weight, placental weight, menstrual age, perinatal mortality and maternal diastolic blood pressure

Smoking habits of 597 pregnant women were investigated; 48.6% of the women smoked during pregnancy. Percentile birth weight proved to be decreased compared with the Amsterdam birth weight charts. This decrease could be attributed largely to smoking in pregnancy. Mean birth weight was significantly lower in smokers than in nonsmokers (230 g; p less than 0.01). Placental weight and menstrual age were not affected by smoking during pregnancy. A statistically significant higher incidence of hypertension in pregnancy in the nonsmokers group compared with the smokers group (p less than 0.05) was established.     

'Normal but dead': perinatal mortality in non-malformed babies of birthweight 2.5 kg and over in the northern region in 1983

The case notes relating to 75 of the 91 perinatal deaths of nonmalformed babies of birthweight greater than or equal to 2.5 kg born in the Northern Region in 1983 were examined. The major groups involved antepartum deaths of unknown cause (40%), and deaths due to intrapartum anoxia or trauma (35%). A case-control study compared each of the 75 cases with two controls matched for place of birth, obtained by taking the next two babies born in the same maternity unit (excluding perinatal deaths, birthweight less than 2.5 kg, and malformations). Four factors were found to be significantly associated with risk of perinatal death in this group: primigravidity, parity greater than or equal to 3, not booked for antenatal care by 20 weeks, and corrected birthweight less than 3.2 kg (adjusted for gestation). Two further factors were related only to the risk of perinatal death consequent upon intrapartum events: labour post-term and malpresentation in labour. All four factors relevant to the whole group remained independently associated with risk of perinatal death after multivariate analysis by two techniques. Adjusted odds ratios (95% CI) were estimated as: primigravidity 2.1 (1.1 to 4.1); parity three or more 5.7 (1.9 to 17); not booked for antenatal care by 20 weeks 15.7 (3.0 to 81); and corrected birthweight less than 3.25 kg 2.5 (1.3 to 4.6). An avoidable factor, as defined, was detected in 50% of deaths. In 30% of deaths there was an avoidable factor (grade 2) such that absence may have been expected to lead to a different outcome had all other factors remained equal. Of the avoidable factors detected, 61% related to intrapartum management, as did 76% of the grade 2 factors. Most of these involved failure to respond to evidence of fetal distress in labour. The defined group constituted 21% of all perinatal deaths, suggesting that this is an important category, particularly as their potential for normal survival should otherwise have been high.