The use of customised versus population-based birthweight standards in predicting perinatal mortality

The accuracy of international and national fetal growth charts in detecting small-for-gestational-age infants using the Lambda-Mu-Sigma method

Objective

To construct a national fetal growth chart using retrospective data and compared its diagnostic accuracy in predicting SGA at birth with existing international growth charts.

Method

This is a retrospective study where datasets from May 2011 to Apr 2020 were extracted to construct the fetal growth chart using the Lambda-Mu-Sigma method. SGA is defined as birth weight <10th centile. The local growth chart's diagnostic accuracy in detecting SGA at birth was evaluated using datasets from May 2020 to Apr 2021 and was compared with the WHO, Hadlock, and INTERGROWTH-21st charts. Balanced accuracy, sensitivity, and specificity were reported.

Results

A total of 68,897 scans were collected and five biometric growth charts were constructed. Our national growth chart achieved an accuracy of 69% and a sensitivity of 42% in identifying SGA at birth. The WHO chart showed similar diagnostic performance as our national growth chart, followed by the Hadlock (67% accuracy and 38% sensitivity) and INTERGROWTH-21st (57% accuracy and 19% sensitivity). The specificities for all charts were 95-96%. All growth charts showed higher accuracy in the third trimester, with an improvement of 8-16%, as compared to that in the second trimester.

Conclusion

Using the Hadlock and INTERGROWTH-21st chart in the Malaysian population may results in misdiagnose of SGA. Our population local chart has slightly higher accuracy in predicting preterm SGA in the second trimester which can enable earlier intervention for babies who are detected as SGA. All growth charts' diagnostic accuracies were poor in the second trimester, suggesting the need of improvising alternative techniques for early detection of SGA to improve fetus outcomes.

Maternal risk factors associated with term low birth weight in India: A review

Low birth weight is one of the leading factors for infant morbidity and mortality. To a large extent affect, various maternal risk factors are associated with pregnancy outcomes by increasing odds of delivering an infant with low birth weight. Despite this association, understanding the maternal risk factors affecting term low birth weight has been a challenging task. To date, limited studies have been conducted in India that exert independent magnitude of these effects on term low birth weight. The aim of this review is to examine the current knowledge of maternal risk factors that contribute to term low birth weight in the Indian population. In order to identify the potentially relevant articles, an extensive literature search was conducted using PubMed, Goggle Scholar and IndMed databases (1993 – Dec 2020). Our results indi­cate that maternal age, educational status, socio-economic status, ethnicity, parity, pre-pregnancy weight, maternal stature, maternal body mass index, obstetric history, maternal anaemia, gestational weight gain, short pregnancy outcome, hypertension during pregnancy, infection, antepartum haemorrhage, tobacco consumption, maternal occupation, maternal psychological stress, alcohol consumption, antenatal care and mid-upper arm circumference have all independent effects on term low birth weight in the Indian pop­ulation. Further, we argue that exploration for various other dimensions of maternal factors and underlying pathways can be useful for a better understanding of how it exerts independent association on term low birth weight in the Indian sub-continent.

[Ante- and postnatal growth charts in France - guidelines for clinical practice from the Collège national des gynécologues et obstétriciens français (CNGOF) and from the Société française de néonatologie (SFN)]

OBJECTIVE

To recommend the most appropriate biometric charts for the detection of antenatal growth abnormalities and postnatal growth surveillance.

METHODS

Elaboration of specific questions and selection of experts by the organizing committee to answer these questions; analysis of the literature by experts and drafting conclusions by assigning a recommendation (strong or weak) and a quality of evidence (high, moderate, low, very low) and for each question; all these recommendations have been subject to multidisciplinary external review (obstetrician gynecologists, pediatricians). The objective for the reviewers was to verify the completeness of the literature review, to verify the levels of evidence established and the consistency and applicability of the resulting recommendations. The overall review of the literature, quality of evidence and recommendations were revised to take into consideration comments from external reviewers.

RESULTS

Antenatally, it is recommended to use all WHO fetal growth charts for EFW and common ultrasound biometric measurements (strong recommendation; low quality of evidence). Indeed, in comparison with other prescriptive curves and descriptive curves, the WHO prescriptive charts show better performance for the screening of SGA (Small for Gestational Age) and LGA (Large for Gestational Age) with adequate proportions of fetuses screened at extreme percentiles in the French population. It also has the advantages of having EFW charts by sex and biometric parameters obtained from the same perspective cohort of women screened by qualified sonographers who measured the biometric parameters according to international standards. Postnatally, it is recommended to use the updated Fenton charts for the assessment of birth measurements and for growth monitoring in preterm infants (strong recommendation; moderate quality of evidence) and for the assessment of birth measurements in term newborn (expert opinion).

CONCLUSION

It is recommended to use WHO fetal growth charts for antenatal growth monitoring and Fenton charts for the newborn.

Evaluation of the Growth Assessment Protocol (GAP) for antenatal detection of small for gestational age: The DESiGN cluster randomised trial

BACKGROUND

Antenatal detection and management of small for gestational age (SGA) is a strategy to reduce stillbirth. Large observational studies provide conflicting results on the effect of the Growth Assessment Protocol (GAP) in relation to detection of SGA and reduction of stillbirth; to the best of our knowledge, there are no reported randomised control trials. Our aim was to determine if GAP improves antenatal detection of SGA compared to standard care.

METHODS AND FINDINGS

This was a pragmatic, superiority, 2-arm, parallel group, open, cluster randomised control trial. Maternity units in England were eligible to participate in the study, except if they had already implemented GAP. All women who gave birth in participating clusters (maternity units) during the year prior to randomisation and during the trial (November 2016 to February 2019) were included. Multiple pregnancies, fetal abnormalities or births before 24+1 weeks were excluded. Clusters were randomised to immediate implementation of GAP, an antenatal care package aimed at improving detection of SGA as a means to reduce the rate of stillbirth, or to standard care. Randomisation by random permutation was stratified by time of study inclusion and cluster size. Data were obtained from hospital electronic records for 12 months prerandomisation, the washout period (interval between randomisation and data collection of outcomes), and the outcome period (last 6 months of the study). The primary outcome was ultrasound detection of SGA (estimated fetal weight <10th centile using customised centiles (intervention) or Hadlock centiles (standard care)) confirmed at birth (birthweight <10th centile by both customised and population centiles). Secondary outcomes were maternal and neonatal outcomes, including induction of labour, gestational age at delivery, mode of birth, neonatal morbidity, and stillbirth/perinatal mortality. A 2-stage cluster-summary statistical approach calculated the absolute difference (intervention minus standard care arm) adjusted using the prerandomisation estimate, maternal age, ethnicity, parity, and randomisation strata. Intervention arm clusters that made no attempt to implement GAP were excluded in modified intention to treat (mITT) analysis; full ITT was also reported. Process evaluation assessed implementation fidelity, reach, dose, acceptability, and feasibility. Seven clusters were randomised to GAP and 6 to standard care. Following exclusions, there were 11,096 births exposed to the intervention (5 clusters) and 13,810 exposed to standard care (6 clusters) during the outcome period (mITT analysis). Age, height, and weight were broadly similar between arms, but there were fewer women: of white ethnicity (56.2% versus 62.7%), and in the least deprived quintile of the Index of Multiple Deprivation (7.5% versus 16.5%) in the intervention arm during the outcome period. Antenatal detection of SGA was 25.9% in the intervention and 27.7% in the standard care arm (adjusted difference 2.2%, 95% confidence interval (CI) -6.4% to 10.7%; p = 0.62). Findings were consistent in full ITT analysis. Fidelity and dose of GAP implementation were variable, while a high proportion (88.7%) of women were reached. Use of routinely collected data is both a strength (cost-efficient) and a limitation (occurrence of missing data); the modest number of clusters limits our ability to study small effect sizes.

CONCLUSIONS

In this study, we observed no effect of GAP on antenatal detection of SGA compared to standard care. Given variable implementation observed, future studies should incorporate standardised implementation outcomes such as those reported here to determine generalisability of our findings.

TRIAL REGISTRATION

This trial is registered with the ISRCTN registry, ISRCTN67698474.

Predictive performance of newborn small for gestational age by a United States intrauterine vs birthweight-derived standard for short-term neonatal morbidity and mortality

BACKGROUND

The use of birthweight standards to define small for gestational age may fail to identify neonates affected by poor fetal growth as they include births associated with suboptimal fetal growth.

OBJECTIVE

This study aimed to compare intrauterine vs birthweight-derived standards to define newborn small for gestational age to predict neonatal morbidity and mortality.

STUDY DESIGN

This was a secondary analysis of a multicenter observational study of 118,422 births. Live-born singleton, nonanomalous newborns born at 23 to 41 weeks of gestation were included. Those with missing gestational age estimation or without a first- or second-trimester ultrasound to confirm dating, birthweight, or neonatal outcome data were excluded. Birthweight percentile was computed using an intrauterine standard (Hadlock) and a birthweight-derived standard (Olsen). We compared the test characteristics of small for gestational age (birthweight of <10th percentile) by each standard to predict a composite neonatal morbidity and mortality outcome (death before discharge, neonatal intensive care unit admission >48 hours, respiratory distress syndrome, sepsis, necrotizing enterocolitis, grade 3 or 4 intraventricular hemorrhage, or seizures). Severe composite morbidity was analyzed as a secondary outcome and was defined as death, neonatal intensive care unit admission >7 days, necrotizing enterocolitis, grade 3 or 4 intraventricular hemorrhage, or seizures. The areas under the curve using receiver-operating characteristic methodology and proportions of the primary outcome by small for gestational age status were compared by gestational age category at birth (<34, 34 0/7 to 36 6/7, ≥37 weeks).

RESULTS

Of 115,502 mother-newborn dyads in the parent study, 78,203 (67.7%) were included, with most exclusions occurring because of missing or inadequate dating information, multiple gestations, or delivery outside the gestational age range. The primary composite outcome occurred in 9.5% (95% confidence interval, 9.3-9.7), and the severe composite outcome occurred in 5.3% (95% confidence interval, 5.1-5.4). Small for gestational age was diagnosed by intrauterine and birthweight-derived standards in 14.8% and 7.4%, respectively (P<.001). Neonates considered small for gestational age only by the intrauterine standard experienced the primary outcome more than twice as often as those considered non-small for gestational age by both standards (18.4% vs 7.9%; P<.001). For the prediction of the primary outcome, small for gestational age by the intrauterine standard had higher sensitivity (29% vs 15%; P<.001) but lower specificity (87% vs 93%; P<.001) than by the birthweight standard. Both standards had weak performance overall, although the intrauterine standard had a higher area under the curve (0.58 vs 0.53; P<.001). When subanalyzed by gestational age at birth, the difference in areas under the curve was only present among preterm deliveries 34 to 36 competed weeks. Neither standard demonstrated any discrimination for morbidity prediction among term births (area under the curve, 0.50 for both). When the prediction of severe morbidity was compared, the intrauterine still had better overall prediction than the birthweight standard (areas under the curve, 0.65 vs 0.57; P<.001), although this also varied by gestational age at birth.

CONCLUSION

Among nonanomalous neonates, neither intrauterine nor birthweight-derived standards for small for gestational age accurately predicted neonatal morbidity and mortality, with no discriminatory ability at term. Small for gestational age intrauterine standards performed better than birthweight standards.

A prenatal standard for fetal weight improves the prenatal diagnosis of small for gestational age fetuses in pregnancies at increased risk

Objective

Our aim was to assess diagnostic accuracy in the prediction of small for gestational age (SGA <10th centile) and fetal growth restricted (FGR) (SGA <3rd centile) fetuses using three different sonographic methods in pregnancies at increased risk of fetal growth restriction: 1) fetal abdominal circumference (AC) z-scores, 2) estimated fetal weight (EFW) z-scores according to postnatal reference standard; 3) EFW z-scores according to a prenatal reference standard.

Methods

Singleton pregnancies at increased risk of fetal growth restriction seen in two university hospitals between 2014 and 2015 were studied retrospectively. EFW was calculated using formulas proposed by the INTERGROWTH-21st project and Hadlock; data derived from publications by the INTEGROWTH-twenty-first century project and Hadlock were used to calculate z-scores (AC and EFW). The accuracy of different methods was calculated and compared.

Results

The study group included 406 patients. Prenatal standard EFW z-scores derived from INTERGROWTH-21st project and Hadlock and co-workers performed similarly and were more accurate in identifying SGA infants than using AC z-scores or a postnatal reference standard. The subgroups analysis demonstrated that EFW prenatal standard was more or similarly accurate compared to other methods across all subgroups, defined by gestational age and birth weight.

Conclusions

Prenatal standard EFW z-scores derived from either INTERGROWTH-21 st project or Hadlock and co-workers publications demonstrated a statistically significant advantage over other biometric methods in the diagnosis of SGA fetuses.

Customized versus Population Growth Standards for Morbidity and Mortality Risk Stratification Using Ultrasonographic Fetal Growth Assessment at 22 to 29 Weeks' Gestation

OBJECTIVE

The aim of study is to compare the performance of ultrasonographic customized and population fetal growth standards for prediction adverse perinatal outcomes.

STUDY DESIGN

This was a secondary analysis of the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be, in which l data were collected at visits throughout pregnancy and after delivery. Percentiles were assigned to estimated fetal weights (EFWs) measured at 22 to 29 weeks using the Hadlock population standard and a customized standard (www.gestation.net). Areas under the curve were compared for the prediction of composite and severe composite perinatal morbidity using EFW percentile.

RESULTS

Among 8,701 eligible study participants, the population standard diagnosed more fetuses with fetal growth restriction (FGR) than the customized standard (5.5 vs. 3.5%, p < 0.001). Neither standard performed better than chance to predict composite perinatal morbidity. Although the customized performed better than the population standard to predict severe perinatal morbidity (areas under the curve: 0.56 vs. 0.54, p = 0.003), both were poor. Fetuses considered FGR by the population standard but normal by the customized standard had morbidity rates similar to fetuses considered normally grown by both standards.The population standard diagnosed FGR among black women and Hispanic women at nearly double the rate it did among white women (p < 0.001 for both comparisons), even though morbidity was not different across racial/ethnic groups. The customized standard diagnosed FGR at similar rates across groups. Using the population standard, 77% of FGR cases were diagnosed among female fetuses even though morbidity among females was lower (p < 0.001). The customized model diagnosed FGR at similar rates in male and female fetuses.

CONCLUSION

At 22 to 29 weeks' gestation, EFW percentile alone poorly predicts perinatal morbidity whether using customized or population fetal growth standards. The population standard diagnoses FGR at increased rates in subgroups not at increased risk of morbidity and at lower rates in subgroups at increased risk of morbidity, whereas the customized standard does not.

Common maternal and fetal genetic variants show expected polygenic effects on risk of small- or large-for-gestational-age (SGA or LGA), except in the smallest 3% of babies

Babies born clinically Small- or Large-for-Gestational-Age (SGA or LGA; sex- and gestational age-adjusted birth weight (BW) <10th or >90th percentile, respectively), are at higher risks of complications. SGA and LGA include babies who have experienced environment-related growth-restriction or overgrowth, respectively, and babies who are heritably small or large. However, the relative proportions within each group are unclear. We assessed the extent to which common genetic variants underlying variation in birth weight influence the probability of being SGA or LGA. We calculated independent fetal and maternal genetic scores (GS) for BW in 11,951 babies and 5,182 mothers. These scores capture the direct fetal and indirect maternal (via intrauterine environment) genetic contributions to BW, respectively. We also calculated maternal fasting glucose (FG) and systolic blood pressure (SBP) GS. We tested associations between each GS and probability of SGA or LGA. For the BW GS, we used simulations to assess evidence of deviation from an expected polygenic model. Higher BW GS were strongly associated with lower odds of SGA and higher odds of LGA (ORfetal = 0.75 (0.71,0.80) and 1.32 (1.26,1.39); ORmaternal = 0.81 (0.75,0.88) and 1.17 (1.09,1.25), respectively per 1 decile higher GS). We found evidence that the smallest 3% of babies had a higher BW GS, on average, than expected from their observed birth weight (assuming an additive polygenic model: Pfetal = 0.014, Pmaternal = 0.062). Higher maternal SBP GS was associated with higher odds of SGA P = 0.005. We conclude that common genetic variants contribute to risk of SGA and LGA, but that additional factors become more important for risk of SGA in the smallest 3% of babies.

Outcome dependent twin growth curves based on birth weight percentiles for Polish population

OBJECTIVE

The objective of this study is to determine a healthy fetal growth pattern of twins from a Polish population based on an outcome-dependent growth curve.

METHODS

The fetal growth data of live-born twin pregnancies between 25th and 40th week gestation in the period of 1 January 2005 to 31 March 2018 from the database of a tertiary care women's hospital in Western Poland was used to calculate birth weight percentiles. The growth curves of singletons from the same database were used as comparison. Because this study aimed for an outcome-dependent approach for the calculation of fetal growth curves, all babies born that may have high risk of unfavorable outcome were excluded. After application of all exclusion criteria, 1317 records referring to 2634 children were included in our analysis. Growth curves of singletons from the same database were used as reference for this study.

RESULTS

A linear relationship between 10th, 50th, and 90th percentiles and gestational age were found for twins but not for singletons suggesting the different mechanisms of intrauterine growth between singleton and twin pregnancies. Week-to-week weight gain equal to or higher than 150 g in twins also predict a favorable outcome in absence of other pathologies.

CONCLUSION

The calculated outcome-dependent fetal growth curves for twins in this study may help in the accurate diagnosis of small or large twin fetuses for their gestational age in this Western Poland population.

The DESiGN trial (DEtection of Small for Gestational age Neonate), evaluating the effect of the Growth Assessment Protocol (GAP): study protocol for a randomised controlled trial

Background

Stillbirth rates in the United Kingdom (UK) are amongst the highest of all developed nations. The association between small-for-gestational-age (SGA) foetuses and stillbirth is well established, and observational studies suggest that improved antenatal detection of SGA babies may halve the stillbirth rate. The Growth Assessment Protocol (GAP) describes a complex intervention that includes risk assessment for SGA and screening using customised fundal-height growth charts. Increased detection of SGA from the use of GAP has been implicated in the reduction of stillbirth rates by 22%, in observational studies of UK regions where GAP uptake was high. This study will be the first randomised controlled trial examining the clinical efficacy, health economics and implementation of the GAP programme in the antenatal detection of SGA.

Methods/design

In this randomised controlled trial, clusters comprising a maternity unit (or National Health Service Trust) were randomised to either implementation of the GAP programme, or standard care. The primary outcome is the rate of antenatal ultrasound detection of SGA in infants found to be SGA at birth by both population and customised standards, as this is recognised as being the group with highest risk for perinatal morbidity and mortality. Secondary outcomes include antenatal detection of SGA by population centiles, antenatal detection of SGA by customised centiles, short-term maternal and neonatal outcomes, resource use and economic consequences, and a process evaluation of GAP implementation. Qualitative interviews will be performed to assess facilitators and barriers to implementation of GAP.

Discussion

This study will be the first to provide data and outcomes from a randomised controlled trial investigating the potential difference between the GAP programme compared to standard care for antenatal ultrasound detection of SGA infants. Accurate information on the performance and service provision requirements of the GAP protocol has the potential to inform national policy decisions on methods to reduce the rate of stillbirth.

Trial registration

Primary registry and trial identifying number: ISRCTN 67698474. Registered on 2 November 2016.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3242-6) contains supplementary material, which is available to authorized users.

The relationship between low birthweight and childhood health: disparities by race, ethnicity, and national origin

PURPOSE

Racial/ethnic disparities in rates of low birthweight (LBW) are well established, as are racial/ethnic differences in health outcomes over the life course. Yet, there is little empirical work examining whether the consequences of LBW for subsequent child health vary by race, ethnicity, and national origin.

METHODS

Using data from the 1998-2016 National Health Interview Survey, we examined whether racial, ethnic, and national differences existed in the association between LBW and subsequent health outcomes, namely being diagnosed with a developmental disability, asthma diagnosis, and poorer general health.

RESULTS

Children born with LBW consistently had poorer health relative to children born with normal birthweight. There was no systematic evidence that the linkages between LBW and subsequent health were weaker for one racial/ethnic/national origin group relative to others.

CONCLUSIONS

LBW was associated with subsequent poorer health. There was no systematic evidence that the link between LBW and subsequent child health were weaker for one racial/ethnic/national origin group relative to others. Together, these findings highlight the importance of reducing race/ethnic disparities in rates of LBW as a way of eradicating inequalities in childhood health.

Customized fetal growth standard compared with the INTERGROWTH-21st century standard at predicting small-for-gestational-age neonates

INTRODUCTION

The INTERGROWTH-21st project (IG-21) was recently performed aiming to provide a universal benchmark for comparing fetal growth across different ethnicities. Our aim was to compare the IG-21 with a customized standard for predicting pregnancies at risk for neonatal small-for-gestational age (SGA) and adverse outcomes.

MATERIAL AND METHODS

This was a prospective cohort study including singleton pregnancies presenting for fetal growth assessment between 26 and 36 weeks of gestation. Fetal growth restriction was defined as estimated fetal weight <10th centile for gestational age using IG-21 and a customized standard. Neonatal SGA was defined as birthweight <10th centile for gestational age by the Alexander chart. Primary outcome was the prediction of neonatal SGA. Secondary outcomes included a composite of adverse neonatal outcomes. The discriminatory ability of each growth standard was compared using area under receiver operating characteristic curves (AUC).

RESULTS

Of 1054 pregnancies meeting the inclusion criteria, the incidence of neonatal SGA was 139 (13.2%), and a composite adverse neonatal outcome occurred in 300 (28.4%). The sensitivity of the customized standard (38.8%) was higher than that of IG-21 (24.5%) for predicting neonatal SGA, with AUC (95% CI) of 0.67 (0.63-0.71) for customized vs 0.62 (0.58-0.65) for IG-21; P = .003. Both standards were comparable in predicting the composite adverse neonatal outcomes: AUC (95% CI) 0.52 (0.50-0.55) for customized vs 0.51 (0.50-0.53) for IG-21; P = 0.25.

CONCLUSIONS

Both growth standards had modest performance in detecting neonatal SGA and were poor at predicting short-term adverse neonatal outcome.

Neurodevelopment at Age 10 Years of Children Born <28 Weeks With Fetal Growth Restriction

OBJECTIVES

We sought to evaluate the relationships between fetal growth restriction (FGR) (both severe and less severe) and assessments of cognitive, academic, and adaptive behavior brain function at age 10 years.

METHODS

At age 10 years, the Extremely Low Gestational Age Newborns Cohort Study assessed the cognitive function, academic achievement, social-communicative function, psychiatric symptoms, and overall quality of life of 889 children born before 28 weeks' gestation. A pediatric epileptologist also interviewed parents as part of a seizure evaluation. The 52 children whose birth weight z scores were <-2 were classified as having severe FGR, and the 113 whose birth weight z scores were between -2 and -1 were considered to have less severe FGR.

RESULTS

The more severe the growth restriction in utero, the lower the level of function on multiple cognitive and academic achievement assessments performed at age 10 years. Growth-restricted children were also more likely than their extremely preterm peers to have social awareness impairments, autistic mannerisms, autism spectrum diagnoses, difficulty with semantics and speech coherence, and diminished social and psychosocial functioning. They also more frequently had phobias, obsessions, and compulsions (according to teacher, but not parent, report).

CONCLUSIONS

Among children born extremely preterm, those with severe FGR appear to be at increased risk of multiple cognitive and behavioral dysfunctions at age 10 years, raising the possibility that whatever adversely affected their intrauterine growth also adversely affected multiple domains of cognitive and neurobehavioral development.

Impact of customized growth curves on screening for small for gestational age twins

OBJECTIVE

The choice of a growth curve determines the screening for small-for-gestational-age (SGA) fetuses and little data is available on SGA twins. Our aim was to evaluate small-for-gestational-age (SGA) detection rate in twin pregnancies and assess whether the use of a customized curve allowed better identification of SGA fetuses.

STUDY DESIGN

Retrospective study including all twins between 2010 and 2013. Two groups were formed: the SGA and the non-SGA group. Four curves were compared: Hadlock's curve, a customized curve, EPOPé M0 and EPOPé M1. We defined a composite neonatal complication criterion (transfer to intensive care unit, respiratory distress and death).

RESULT

472 fetuses were included with a 34.3% prevalence of SGA. Hadlock's curve showed better sensitivity for the detection of SGA <10th percentile (67.3% vs. 63%, 59.9% and 57.4% respectively). Diagnostic Odd Ratio were comparable for the detection of SGA. For the composite variable, there was a significant difference between the 2 groups using a customized curve adjusted for fetal sex (EPOPé M1).

CONCLUSION

The EPOPé (M0 and M1) and customized curves do not improve screening for SGA infants below the 10th percentile. The reduced effectiveness of customized curves can be related to the greater impact of placentation or cord insertion on the potential for fetal growth.

2500-g Low Birth Weight Cutoff: History and Implications for Future Research and Policy

Purpose To research the origins of the 2500 g cutoff for low birth weight and the evolution of indicators to identify newborns at high mortality risk. Description Early research concluded "prematurity", measured mainly through birth weight, was responsible for increased health risks. The World Health Organization's original prematurity definition was birth weight ≤2500 g. 1960s research clarified the difference between gestational age and birth weight leading to questions of the causal role of birth weight for health outcomes. Focus turned to two etiologies of low birth weight, preterm births and intrauterine growth restriction, which were both causally associated with morbidity and mortality but through different pathways; a standard cutoff based on gestational age or customized cutoff was debated. Assessment While low birth weight can be due to preterm or intrauterine growth restriction (or both), the historic 2500 g cutoff remains the standard by which the majority of policy makers define low birth weight and use it to predict perinatal and infant adverse outcomes. Conclusion Current efforts to refocus research on preterm births and poor intrauterine growth are important to understanding the direct causes of mortality rather than low birth weight as a convenient surrogate. Such distinctions also allow researchers and practitioners to test and target interventions outcomes more effectively.

Customized Fetal Growth Charts for Parents' Characteristics, Race, and Parity by Quantile Regression Analysis: A Cross-sectional Multicenter Italian Study

OBJECTIVES

The purpose of this study was to construct fetal biometric charts between 16 and 40 weeks' gestation that were customized for parental characteristics, race, and parity, using quantile regression analysis.

METHODS

In a multicenter cross-sectional study, 8070 sonographic examinations from low-risk pregnancies between 16 and 40 weeks' gestation were analyzed. The fetal measurements obtained were biparietal diameter, head circumference, abdominal circumference, and femur diaphysis length. Quantile regression was used to examine the impact of parental height and weight, parity, and race across biometric percentiles for the fetal measurements considered.

RESULTS

Paternal and maternal height were significant covariates for all of the measurements considered (P < .05). Maternal weight significantly influenced head circumference, abdominal circumference, and femur diaphysis length. Parity was significantly associated with biparietal diameter and head circumference. Central African race was associated with head circumference and femur diaphysis length, whereas North African race was only associated with femur diaphysis length.

CONCLUSIONS

In this study we constructed customized biometric growth charts using quantile regression in a large cohort of low-risk pregnancies. These charts offer the advantage of defining individualized normal ranges of fetal biometric parameters at each specific percentile corrected for parental height and weight, parity, and race. This study supports the importance of including these variables in routine sonographic screening for fetal growth abnormalities.

Birth-weight charts and immigrant populations: A critical review

There is an increasing body of literature focusing on differences in newborn size between different population subgroups defined by racial, ethnic, and immigration status. The interpretation of these differences as pathological or as merely reflecting normal variability is not straightforward and may have consequences for the provision of obstetric and neonatal care to minority populations. In this review, we critically assess some methodological issues affecting the assessment of newborn size and their potential implications for minority populations. In particular, we discuss the pros and cons of different types of newborn birth-weight (BW) charts (i.e., single local population-based references, minority-specific references, and a single international standard) to determine abnormal newborn size, with emphasis on immigrant populations. We conclude that size alone is not enough to inform clinical decisions and that all newborn size charts should be used as screening tools, not as diagnostic tools. Parental minority status may be regarded as a marker and used to further inquire about individual risk factors, particularly among immigrants who may not have a complete medical history in the new country. Finally, we outline areas for further research and recommendations for clinical practice.

An adjustable fetal weight standard for twins: a statistical modeling study

BACKGROUND

It is a common practice to use a singleton fetal growth standard to assess twin growth. We aim to create a twin fetal weight standard which is also adjustable for race/ethnicity and other factors.

METHODS

Over half a million twin births of low risk pregnancies in the US, from 1995 to 2004, were used to construct a fetal weight standard. We used the Hadlock's fetal growth standard and the proportionality principle to make the standard adjustable for other factors such as race/ethnicity. We validated the standard in different race/ethnicities in the US and against previously published curves from around the world.

RESULTS

The adjustable fetal weight standard has an excellent match with the observed birthweight data in non-Hispanic White, non-Hispanic Black, Hispanics, and Asian from 24 to 38 weeks gestation. It also had a very good fit with cross-sectional data from Australia and Norway, and a longitudinal standard from Brazil. However, our model-based 10th and 90th percentiles differed substantially from studies in Japan and US that used the last menstrual period for estimate of gestational age.

CONCLUSION

The adjustable fetal weight standard for twins is a flexible tool and can be used in different populations.

Customized versus Population-Based Birth Weight References for Predicting Fetal and Neonatal Undernutrition

Objectives: The aim of our study was to construct a model of customized birth weight curves based on a Spanish population and to compare the ability of this customized model to our population-based chart to predict a neonatal ponderal index (PI) <10th percentile. Methods: We developed a model that can predict the 10th percentile for a fetus according to gestational age and gender as well as maternal weight, height, and age. We compared the ability of this customized model to that of our own population-based model to predict a neonatal PI <10th percentile. Data from a large database were used (32,854 live newborns, from 1993 through 2012). Only singleton pregnancies with a gestational age at delivery of 32-42 weeks were included. Results: In the entire pregnant population, the customized method was superior to the population-based method for detecting newborns with a PI <10th percentile (sensitivity: 55 vs. 40.96%; specificity: 99.6 vs. 91.23%; positive predictive value: 11.49 vs. 9.55%, and negative predictive value: 98.84 vs. 98.55%, respectively). In pregnant women with a BMI >90th percentile, the sensitivity was 75%, compared to 50% in the population-based method. In pregnant women with a height >90th percentile, the sensitivity was almost as high as in the population-based method (61.53 vs. 33.33%). Conclusion: The customized birth weight curve is superior to the population-based method for the detection of newborns with a PI <10th percentile. This is especially the case in women in the higher scales of height and weight as well as in preterm babies.

Small-for-gestational age and large-for-gestational age thresholds to predict infants at risk of adverse delivery and neonatal outcomes: are current charts adequate? An observational study from the Born in Bradford cohort

OBJECTIVES

Construct an ethnic-specific chart and compare the prediction of adverse outcomes using this chart with the clinically recommended UK-WHO and customised birth weight charts using cut-offs for small-for-gestational age (SGA: birth weight <10th centile) and large-for-gestational age (LGA: birth weight >90th centile).

DESIGN

Prospective cohort study.

SETTING

Born in Bradford (BiB) study, UK.

PARTICIPANTS

3980 White British and 4448 Pakistani infants with complete data for gestational age, birth weight, ethnicity, maternal height, weight and parity.

MAIN OUTCOME MEASURES

Prevalence of SGA and LGA, using the three charts and indicators of diagnostic utility (sensitivity, specificity and area under the receiver operating characteristic (AUROC)) of these chart-specific cut-offs to predict delivery and neonatal outcomes and a composite outcome.

RESULTS

In White British and Pakistani infants, the prevalence of SGA and LGA differed depending on the chart used. Increased risk of SGA was observed when using the UK-WHO and customised charts as opposed to the ethnic-specific chart, while the opposite was apparent when classifying LGA infants. However, the predictive utility of all three charts to identify adverse clinical outcomes was poor, with only the prediction of shoulder dystocia achieving an AUROC>0.62 on all three charts.

CONCLUSIONS

Despite being recommended in national clinical guidelines, the UK-WHO and customised birth weight charts perform poorly at identifying infants at risk of adverse neonatal outcomes. Being small or large may increase the risk of an adverse outcome; however, size alone is not sensitive or specific enough with current detection to be useful. However, a significant amount of missing data for some of the outcomes may have limited the power needed to determine true associations.

Shining light in dark corners: diagnosis and management of late-onset fetal growth restriction

Fetal growth restriction (FGR) is the single biggest risk factor for stillbirth. In the absence of any effective treatment for fetal growth restriction, the mainstay of management is close surveillance and timely delivery. While such statements are almost self-evident, the daily clinical challenge of late-onset fetal growth restriction remains; the competing priorities of minimising stillbirth risk, while avoiding excessive obstetric intervention and the neonatal sequelae of iatrogenic preterm birth. This dilemma is made harder because the tools for late-onset FGR diagnosis and surveillance compare poorly to those used in early-onset FGR; screening tests in early pregnancy have limited predictive value; most cases escape clinical detection, a phenomenon set to worsen given the obesity epidemic; there is a failure of consensus on the definition of small for gestational age, and ancillary tools, such as umbilical artery Doppler--of value in identification of preterm FGR--are less useful in the late-preterm period and at term. Most importantly, the problem is common; 96% of all births occur after 32 weeks. This means a poor noise/signal ratio of any test or management algorithm will inevitably have large clinical consequences. Into such a dark corner, we cast some light; a summary on diagnostic criteria, new developments to improve the diagnosis of late-onset FGR and a suggested approach to management.

Size at birth by gestational age and hospital mortality in very preterm infants: results of the area-based ACTION project

BACKGROUND

Size at birth is an important predictor of neonatal outcomes, but there are inconsistencies on the definitions and optimal cut-offs.

AIMS

The aim of this study is to compute birth size percentiles for Italian very preterm singleton infants and assess relationship with hospital mortality.

STUDY DESIGN

Prospective area-based cohort study.

SUBJECTS

All singleton Italian infants with gestational age 22-31 weeks admitted to neonatal care in 6 Italian regions (Friuli Venezia-Giulia, Lombardia, Marche, Tuscany, Lazio and Calabria) (n. 1605).

OUTCOME MEASURE

Hospital mortality.

METHODS

Anthropometric reference charts were derived, separately for males and females, using the lambda (λ) mu (μ) and sigma (σ) method (LMS). Logistic regression analysis was used to estimate mortality rates by gestational age and birth weight centile class, adjusting for sex, congenital anomalies and region.

RESULTS

At any gestational age, mortality decreased as birth weight centile increased, with lowest values observed between the 50th and the 89th centiles interval. Using the 75th-89th centile class as reference, adjusted mortality odds ratios were 7.94 (95% CI 4.18-15.08) below 10th centile; 3.04 (95% CI 1.63-5.65) between the 10th and 24th; 1.96 (95% CI 1.07-3.62) between the 25th and the 49th; 1.25 (95% CI 0.68-2.30) between the 50(h) and the 74th; and 2.07 (95% CI 1.01-4.25) at the 90th and above.

CONCLUSIONS

Compared to the reference, we found significantly increasing adjusted risk of death up to the 49th centile, challenging the usual 10th centile criterion as risk indicator. Continuous measures such as the birthweight z-score may be more appropriate to explore the relationship between growth retardation and adverse perinatal outcomes.

Effect of cigarette smoking on vascular flows in pregnancies complicated by intrauterine growth restriction

Exposure to tobacco smoke during pregnancy may result in intrauterine growth restriction (IUGR). In the study, the effect of tobacco smoke on vascular flows in the middle cerebral artery, umbilical artery, ductus venosus in fetuses and uterine artery in pregnancies complicated by IUGR was investigated. The study subjects were divided into three groups: smoking women with IUGR (n=31), women with idiopathic IUGR (n=28) and healthy controls (n=50). Fetal biometry and flow parameters were measured. Concentration of heavy metals and antioxidants was tested in maternal blood and fetal umbilical cord blood. The Student t test and multiple regression analysis were used. Cotinine and cadmium concentrations were significantly higher in smokers (55.23±54.23, 1.52±0.9), while metallothionein was significantly higher (22.94±8.64) in the idiopathic IUGR group. Strong correlations between cotinine and cadmium concentrations and cerebral-umbilical index were found. Long-term exposure to tobacco smoke deteriorates flows in vital fetal vessels.

Assessment of fetal growth by customized growth charts

Customized fetal growth charts take account of the individual variation in the fetal growth potential based on non-pathological maternal and fetal characteristics. Application of these customized weight charts might improve the distinction between pathological growth-restricted fetuses and fetuses that are small but have reached their growth potential. Current models for customized growth standards have been based on birth weight and fetal growth data. Variables used for customization are gestational age, maternal age, parity, ethnicity, height, weight and fetal sex. Thus far, it remains controversial whether these maternal and fetal characteristics used for customization are strong enough predictors for fetal growth on an individual level and are truly physiological characteristics. The currently available customized growth charts might be of benefit for use in epidemiological studies and clinical practice. Further studies are needed to validate these customized growth models and to examine whether and to what extend they improve identification of children that are at risk for morbidity in the perinatal period and later in life.

Risk of adverse outcomes among infants of immigrant women according to birth-weight curves tailored to maternal world region of origin

BACKGROUND

Infants of immigrant women in Western nations generally have lower birth weights than infants of native-born women. Whether this difference is physiologic or pathological is unclear. We determined whether the use of birth-weight curves tailored to maternal world region of origin would discriminate adverse neonatal and obstetric outcomes more accurately than a single birth-weight curve based on infants of Canadian-born women.

METHODS

We performed a retrospective cohort study of in-hospital singleton live births (328,387 to immigrant women, 761,260 to nonimmigrant women) in Ontario between 2002 and 2012 using population health services data linked to the national immigration database. We classified infants as small for gestational age (<10th percentile) or large for gestational age (≥90th percentile) using both Canadian and world region-specific birth-weight curves and compared associations with adverse neonatal and obstetric outcomes.

RESULTS

Compared with world region-specific birth-weight curves, the Canadian curve classified 20 431 (6.2%) additional newborns of immigrant women as small for gestational age, of whom 15,467 (75.7%) were of East or South Asian descent. The odds of neonatal death were lower among small-for-gestational-age infants of immigrant women than among those of nonimmigrant women based on the Canadian birth-weight curve (adjusted odds ratio [OR] 0.83, 95% confidence interval [CI] 0.72-0.95), but higher when small for gestational age was defined by the world region-specific curves (adjusted OR 1.24, 95% CI 1.08-1.42). Conversely, the odds of some adverse outcomes were lower among large-for-gestational-age infants of immigrant women than among those of nonimmigrant women based on world region-specific birth-weight curves, but were similar based on the Canadian curve.

INTERPRETATION

World region-specific birth-weight curves seemed to be more appropriate than a single Canadian population-based curve for assessing the risk of adverse neonatal and obstetric outcomes among small- and large-for-gestational-age infants born to immigrant women, especially those from the East and South Asian regions.

Identification of pathologically small fetuses using customized, ultrasound and population-based growth norms

OBJECTIVES

Fetal growth restriction is a strong risk factor for stillbirth. We compared the performance of three fetal growth curves - customized, ultrasound (Hadlock) and population - in identifying abnormally grown fetuses at risk of stillbirth.

METHODS

We performed a case-control study of singleton stillbirths (delivered between 2000 and 2010) at one center. Four liveborn controls were randomly identified for each stillbirth. Ultrasound-estimated fetal weight within 1 month prior to delivery was used to calculate growth percentiles for each fetus using three fetal growth norms. Sensitivities and odds ratios for stillbirth, as well as odds of abnormal growth according to formula, were calculated.

RESULTS

There were 49 stillbirths and 197 live births. Using the customized norms, growth of the fetuses destined to be stillborn was bimodal, with both more small-for-gestational-age (SGA; < 10(th) percentile) and large-for-gestational-age (LGA; ≥ 90(th) percentile) fetuses. Odds of being abnormally grown were significantly higher using ultrasound compared with population norms (P = 0.02) but were not statistically different using ultrasound and customized norms (P = 0.21). Sensitivity for identification of SGA on ultrasound as a predictor of stillbirth was higher using customized (39%; 95% CI, 24-54%) or ultrasound (33%; 95% CI, 19-47%), rather than population (14%; 95% CI, 4-25%), norms.

CONCLUSIONS

Among fetuses destined to be stillborn, customized and ultrasound norms identified a greater proportion of both SGA and LGA estimated fetal weights. The customized norms performed best in identifying death among SGA fetuses. These results should be interpreted within the limitations of the study design.

Fetal growth and risk of stillbirth: a population-based case-control study

BACKGROUND

Stillbirth is strongly related to impaired fetal growth. However, the relationship between fetal growth and stillbirth is difficult to determine because of uncertainty in the timing of death and confounding characteristics affecting normal fetal growth.

METHODS AND FINDINGS

We conducted a population-based case-control study of all stillbirths and a representative sample of live births in 59 hospitals in five geographic areas in the US. Fetal growth abnormalities were categorized as small for gestational age (SGA) (<10th percentile) or large for gestational age (LGA) (>90th percentile) at death (stillbirth) or delivery (live birth) using population, ultrasound, and individualized norms. Gestational age at death was determined using an algorithm that considered the time-of-death interval, postmortem examination, and reliability of the gestational age estimate. Data were weighted to account for the sampling design and differential participation rates in various subgroups. Among 527 singleton stillbirths and 1,821 singleton live births studied, stillbirth was associated with SGA based on population, ultrasound, and individualized norms (odds ratio [OR] [95% CI]: 3.0 [2.2 to 4.0]; 4.7 [3.7 to 5.9]; 4.6 [3.6 to 5.9], respectively). LGA was also associated with increased risk of stillbirth using ultrasound and individualized norms (OR [95% CI]: 3.5 [2.4 to 5.0]; 2.3 [1.7 to 3.1], respectively), but not population norms (OR [95% CI]: 0.6 [0.4 to 1.0]). The associations were stronger with more severe SGA and LGA (<5th and >95th percentile). Analyses adjusted for stillbirth risk factors, subset analyses excluding potential confounders, and analyses in preterm and term pregnancies showed similar patterns of association. In this study 70% of cases and 63% of controls agreed to participate. Analysis weights accounted for differences between consenting and non-consenting women. Some of the characteristics used for individualized fetal growth estimates were missing and were replaced with reference values. However, a sensitivity analysis using individualized norms based on the subset of stillbirths and live births with non-missing variables showed similar findings.

CONCLUSIONS

Stillbirth is associated with both growth restriction and excessive fetal growth. These findings suggest that, contrary to current practices and recommendations, stillbirth prevention strategies should focus on both severe SGA and severe LGA pregnancies. Please see later in the article for the Editors' Summary.

Changes in fetal Doppler indices as a marker of failure to reach growth potential at term

OBJECTIVE

To evaluate whether changes in the middle cerebral artery (MCA), umbilical artery (UA) and cerebroplacental ratio (CPR) Doppler indices at term might be used to identify those appropriate-for-gestational-age (AGA) fetuses that are failing to reach their growth potential (FRGP).

METHODS

This was a retrospective cohort study of data obtained in a single tertiary referral center over a 10-year period from 2002 to 2012. The UA pulsatility index (PI), MCA-PI and CPR were recorded between 37+0 and 41+6 weeks within 14 days before delivery. The Doppler parameters were converted into multiples of the median (MoM), adjusting for gestational age, and their correlation with birth-weight (BW) centiles was evaluated by means of regression analysis. Doppler indices were also grouped according to BW quartiles and compared using Kruskal-Wallis and Dunn's post-hoc tests.

RESULTS

The study included 11576 term fetuses, with 8645 (74.7%) classified as AGA. Within the AGA group, fetuses with lower BW had significantly higher UA-PI, lower MCA-PI and lower CPR MoM values. Large-for-gestational-age (LGA) fetuses were considered as the group least likely to be growth-restricted. The CPR MoM < 5(th) centile (0.6765 MoM) in these fetuses was used as a threshold for diagnosing FRGP. Using this definition, in the AGA pregnancies the percentage of fetuses with FRGP was 1% in the 75-90(th) BW centile group, 1.7% in the 50-75(th) centile group, 2.9% in the 25-50(th) centile group and 6.7% in the 10-25(th) centile group.

CONCLUSION

AGA pregnancies may present with fetal cerebral and placental blood flow redistribution indicative of fetal hypoxemia. Fetal Doppler assessment may be of value in detecting AGA pregnancies that are subject to placental insufficiency, fetal hypoxemia and FRGP. Future studies are needed to evaluate the appropriate threshold for the diagnosis of FRGP and the diagnostic performance of this new approach for the management of growth disorders.

Snoring during pregnancy and delivery outcomes: a cohort study

STUDY OBJECTIVE

This cohort study examined the impact of maternal snoring on key delivery outcomes such as mode of delivery, infant birth centile, and small-for-gestational age.

DESIGN

Cohort study.

SETTING

A large tertiary medical center.

PATIENTS OR PARTICIPANTS

Pregnant women in their third trimester were recruited between March 2007 and December 2010.

MEASUREMENTS AND RESULTS

Women were screened for habitual snoring, as a known marker for sleep disordered breathing. Outcome data were obtained from medical records following delivery and birth centiles were calculated. Of 1,673 women, a total of 35% reported habitual snoring (26% with pregnancy-onset snoring and 9% with chronic snoring). After adjusting for confounders, chronic snoring was associated with small-forgestational age (OR 1.65, 95%CI 1.02-2.66, P = 0.041) and elective cesarean delivery (OR 2.25, 95%CI 1.22-4.18, P = 0.008). Pregnancy-onset snoring was associated with emergency cesarean delivery (OR 1.68, 95%CI 1.22-2.30, P = 0.001).

CONCLUSION

Maternal snoring during pregnancy is a risk factor for adverse delivery outcomes including cesarean delivery and small-for-gestational age. Screening pregnant women for symptoms of SDB may provide an early opportunity to identify women at risk of poor delivery outcomes.

CLINICAL TRIALS REGISTRATION

IDENTIFIER: NCT01030003.

Invited commentary: the incremental value of customization in defining abnormal fetal growth status

Reference tools based on birth weight percentiles at a given gestational week have long been used to define fetuses or infants that are small or large for their gestational ages. However, important deficiencies of the birth weight reference are being increasingly recognized. Overwhelming evidence indicates that an ultrasonography-based fetal weight reference should be used to classify fetal and newborn sizes during pregnancy and at birth, respectively. Questions have been raised as to whether further adjustments for race/ethnicity, parity, sex, and maternal height and weight are helpful to improve the accuracy of the classification. In this issue of the Journal, Carberry et al. (Am J Epidemiol. 2013;178(8):1301-1308) show that adjustment for race/ethnicity is useful, but that additional fine tuning for other factors (i.e., full customization) in the classification may not further improve the ability to predict infant morbidity, mortality, and other fetal growth indicators. Thus, the theoretical advantage of full customization may have limited incremental value for pediatric outcomes, particularly in term births. Literature on the prediction of short-term maternal outcomes and very long-term outcomes (adult diseases) is too scarce to draw any conclusions. Given that each additional variable being incorporated in the classification scheme increases complexity and costs in practice, the clinical utility of full customization in obstetric practice requires further testing.

Customized versus population-based birth weight charts for the detection of neonatal growth and perinatal morbidity in a cross-sectional study of term neonates

Customized birth weight charts that incorporate maternal characteristics are now being adopted into clinical practice. However, there is controversy surrounding the value of these charts in the prediction of growth and perinatal outcomes. The objective of this study was to assess the use of customized charts in predicting growth, defined by body fat percentage, and perinatal morbidity. A total of 581 term (≥37 weeks' gestation) neonates born in Sydney, Australia, in 2010 were included. Body fat percentage measurements were taken by using air displacement plethysmography. Objective composite measurements of perinatal morbidity were used to identify neonates who had poor outcomes; these data were extracted from medical records. The value of customized charts was assessed by calculating positive predictive values, negative predictive values, and odds ratios with 95% confidence intervals. Customized versus population-based charts did not improve the prediction of either low body fat percentage (59% vs. 66% positive predictive value and 87% vs. 89% negative predictive value, respectively) or high body fat percentage (48% vs. 53% positive predictive value and 90% vs. 89% negative predictive value, respectively). Customized charts were not better than population-based charts at predicting perinatal morbidity (for customized charts, odds ratio = 1.02, 95% confidence interval: 1.01, 1.04; for population-based charts, odds ratio = 1.03, 95% confidence interval: 1.01, 1.05) per percentile decrease in birth weight. Customized birth weight charts do not provide significant improvements over population-based charts in predicting neonatal growth and morbidity.

New population-based references for birth weight, length, and head circumference in singletons and twins from 23 to 43 gestation weeks

BACKGROUND AND OBJECTIVES

Birth size curves are needed for clinical and epidemiological purposes. We constructed birth weight (BW), length (BL), and head circumference (BHC) references, assessed effects of twinness and parity, and defined cut-off points for small, appropriate, and large for gestational age.

MATERIALS AND METHODS

Birth register data of all 753,036 infants born in 1996-2008 in Finland were cleaned to create references reflecting optimal intrauterine growth. The final data included 533,666 singletons and 15,033 twins (median gestation weeks (gws) 40.0 and 37.1, respectively, 41.6% primiparous). Sex-specific BW, BL, and BHC references were constructed from 23 to 43 gws separately for singletons and twins born to primiparous or multiparous mothers. GAMLSS method was used for modelling.

RESULTS

In singletons from 36 gws onwards, increased BW and BL were observed in comparison to previous reference from 1979-1983. Twins diverged from singletons from 30 gws onwards. At 37.0 gws, mean BW was 400 g lower and mean BL 1.2 cm shorter than in singletons. From 30 gws onwards, birth size was larger in infants of multiparous than primiparous mothers.

CONCLUSIONS

Population-based birth size references are available for the evaluation of birth size. Accounting for plurality and parity improves the accuracy of birth size evaluation.

Application of a global reference for fetal-weight and birthweight percentiles in predicting infant mortality

OBJECTIVE

To determine whether the recently published A global reference for fetal-weight and birthweight percentiles (Global Reference) improves small- (SGA), appropriate- (AGA), and large-for-gestational-age (LGA) definitions in predicting infant mortality.

DESIGN

Population-based cohort study.

SETTING

The US Linked Livebirth and Infant Death records between 1995 and 2004.

POPULATION

Singleton births with birthweight >500 g born at 24-41 weeks of gestation.

METHODS

We compared infant mortality rates of SGA, AGA, and LGA infants classified by three different references: the Global Reference; a commonly used birthweight reference; and Hadlock's ultrasound reference.

MAIN OUTCOME MEASURES

Infant mortality rates.

RESULTS

Among 33 997 719 eligible liveborn singleton births, 25% of preterm and 9% of term infants were classified differently for SGA, AGA, and LGA by the Global Reference and the birthweight reference. The Global Reference indicated higher mortality rates in preterm SGA and preterm LGA infants than the birthweight reference. The mortality rate was considerably higher in infants classified as preterm SGA by the Global Reference but not by the birthweight reference, compared with the corresponding infants classified by the birthweight reference but not by the Global Reference (105.7 versus 12.9 per 1000, RR 8.17, 95% CI 7.38-9.06). Yet, the differences in mortality rates were much smaller in term infants than in preterm infants. Black infants had a particularly higher mortality rate than other races in AGA and LGA preterm and term infants.

CONCLUSIONS

In respect to the commonly used birthweight reference, the Global Reference increases the identification of infant deaths by improved classification of abnormal newborn size at birth, and these advantages were more obvious in preterm than in term infants.

Intrauterine growth restriction: effects of physiological fetal growth determinants on diagnosis

The growth of the fetus, which is strongly associated with the outcome of pregnancy, reflects interplay of several physiological and pathological factors. The assessment of fetal growth is based on comparison of birthweight (BW) or estimated fetal weight (EFW) to standards which define reference ranges at a spectrum of gestational ages. Most birthweight standards do not take into account effects of physiological determinants of fetal growth. Additionally, gestational age in many standards is based on the menstrual history and is often inaccurate. Fetal growth norms should be based on an early ultrasound estimate of gestational age. Customized standards, which have included only ultrasound-dated pregnancies, seem to be superior to population-based birthweight norms in predicting perinatal mortality and morbidity. Adjustment for individual variation in customized growth curves reduces false-positive diagnosis of IUGR and may lead to a very significant reduction in intervention for suspected IUGR. Customized growth potential identifies better the risk for adverse outcome than the currently used national standards, but customized charts may fail in detecting growth-restricted stillbirth. An individual's birthweight is the sum of physiological and pathological influences operating during pregnancy. Growth potential norms are a better discriminator of aberrations of fetal growth than population, ultrasound, and customized norms.

Low birth weight, later renal function, and the roles of adulthood blood pressure, diabetes, and obesity in a British birth cohort

Low birth weight has been shown to be associated with later renal function, but it is unclear to what extent this is explained by other established kidney disease risk factors. Here we investigate the roles of diabetes, hypertension, and obesity using data from the Medical Research Council National Survey of Health and Development, a socially stratified sample of 5362 children born in March 1946 in England, Scotland, and Wales, and followed since. The birth weight of 2192 study members with complete data was related to three markers of renal function at age 60-64 (estimated glomerular filtration rate (eGFR) calculated using cystatin C (eGFRcys), eGFR calculated using creatinine and cystatin C (eGFRcr-cys), and the urine albumin-creatinine ratio) using linear regression. Each 1 kg lower birth weight was associated with a 2.25 ml/min per 1.73 m(2) (95% confidence interval 0.80-3.71) lower eGFRcys and a 2.13 ml/min per 1.73 m(2) (0.69-3.58) lower eGFRcr-cys. There was no evidence of an association with urine albumin-creatinine ratio. These associations with eGFR were not confounded by socioeconomic position and were not explained by diabetes or hypertension, but there was some evidence that they were stronger in study members who were overweight in adulthood. Thus, our findings highlight the role of lower birth weight in renal disease and suggest that in those born with lower birth weight particular emphasis should be placed on avoiding becoming overweight.

Customised birthweight models: do they increase identification of at-risk infants?

AIM

The study aims to describe the cohort of women and babies who are classified as small-for-gestational age (SGA) at term by both an Australian customised birthweight model (CBM) and a commonly used population-based standard, and to investigate and compare the utility of these models in identifying babies at risk of experiencing adverse outcomes

METHODS

Routinely collected data on 54 890 singleton-term births at the Mater Mothers' Hospitals, Brisbane, with birthweight less than 4000 g between January 1997 and December 2008, was extracted. Each birth was classified as SGA (<10th centile) or not SGA by either and/or both methods: population-based standards (SGApop ) and CBM (SGAcust ). Babies classified as SGApop , SGAcust or SGAboth were compared with those not classified as SGA by both methods using relative risk and 95% confidence interval, and those only classified as SGAcust were compared with those only classified as SGApop . Maternal demographics, maternal risk factors for fetal growth restriction, pregnancy and labour complications and adverse neonatal outcomes are reported.

RESULTS

 A total of 4768 (8.7%) births were classified as SGApop , while 6479 (11.8%) were SGAcust of whom 4138 (63.9%) were also classified as SGApop . Maternal risk factors such as smoking and hypertension were statistically higher for the SGAcust group when compared with SGApop . For the majority of adverse neonatal outcomes, a trend was noted to increased identification using the CBM.

CONCLUSION

The CBM provides a modest improvement when compared to a population-based standard to identity term infants at birth who are at risk of adverse neonatal outcomes.

A systematic review and meta-analysis to revise the Fenton growth chart for preterm infants

Background

The aim of this study was to revise the 2003 Fenton Preterm Growth Chart, specifically to: a) harmonize the preterm growth chart with the new World Health Organization (WHO) Growth Standard, b) smooth the data between the preterm and WHO estimates, informed by the Preterm Multicentre Growth (PreM Growth) study while maintaining data integrity from 22 to 36 and at 50 weeks, and to c) re-scale the chart x-axis to actual age (rather than completed weeks) to support growth monitoring.

Methods

Systematic review, meta-analysis, and growth chart development. We systematically searched published and unpublished literature to find population-based preterm size at birth measurement (weight, length, and/or head circumference) references, from developed countries with: Corrected gestational ages through infant assessment and/or statistical correction; Data percentiles as low as 24 weeks gestational age or lower; Sample with greater than 500 infants less than 30 weeks. Growth curves for males and females were produced using cubic splines to 50 weeks post menstrual age. LMS parameters (skew, median, and standard deviation) were calculated.

Results

Six large population-based surveys of size at preterm birth representing 3,986,456 births (34,639 births < 30 weeks) from countries Germany, United States, Italy, Australia, Scotland, and Canada were combined in meta-analyses. Smooth growth chart curves were developed, while ensuring close agreement with the data between 24 and 36 weeks and at 50 weeks.

Conclusions

The revised sex-specific actual-age growth charts are based on the recommended growth goal for preterm infants, the fetus, followed by the term infant. These preterm growth charts, with the disjunction between these datasets smoothing informed by the international PreM Growth study, may support an improved transition of preterm infant growth monitoring to the WHO growth charts.

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.

The influence of fetal growth reference standards on assessment of cognitive and academic outcomes of very preterm children

OBJECTIVE

To compare 3 methods of identifying small-for-gestational-age (SGA) status in very preterm children as related to cognitive function and academic outcome.

STUDY DESIGN

There were 1038 singletons in the Epipage Study, born before 33 weeks in 1997 without severe neurosensory impairment, who were classified as SGA when birth weight was below the 10th percentile according to: (1) birth weight (bw) reference: SGA(bw)/appropriate for gestational age (AGA)(bw); (2) intrauterine (intraut) reference: SGA(intraut)/AGA(intraut); and (3) intrauterine reference customized (cust) according to individual characteristics: SGA(cust)/AGA(cust). Cognitive function was assessed by the mental processing composite (MPC) score of the Kaufman Assessment Battery for Children at age 5 and academic achievement by a parental questionnaire at age 8.

RESULTS

Of the children, 15% were SGA(bw), 38% were SGA(intraut), and 39% were SGA(cust). All children SGA(bw) were also SGA(intraut) and SGA(cust). MPC was <85 in 32% of children and 27% had low academic achievement. AGA(bw)/SGA(intraut) children had a significantly increased risk of MPC <85 (adjusted OR 1.74, 95% CI 1.22-2.28) or low academic achievement (adjusted OR 1.64, 95% CI 1.05-2.55) compared with AGA(bw)/AGA(intraut) children. The SGA(cust) group was only slightly different from the SGA(intraut) group.

CONCLUSIONS

An intrauterine reference identified very preterm infants at risk of poor cognitive or academic outcomes better than a birth weight reference. Customization resulted in only slight modifications of the SGA group.