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

Regional references vs. international standards for assessing weight and length by gestational age in Lithuanian neonates

Introduction

There is no global consensus as to which standards are the most appropriate for the assessment of birth weight and length. The study aimed to compare the applicability of regional and global standards to the Lithuanian newborn population by sex and gestational age, based on the prevalence of small or large for gestational age (SGA/LGA).

Materials and Methods

Analysis was performed on neonatal length and weight data obtained from the Lithuanian Medical Birth Register from 1995 to 2015 (618,235 newborns of 24-42 gestational weeks). Their distributions by gestation and sex were estimated using generalized additive models for location, scale, and shape (GAMLSS), and the results were compared with the INTERGROWTH-21st (IG-21) standard to evaluate the prevalence of SGA/LGA (10th/90th centile) at different gestational ages.

Results

The difference in median length at term between the local reference and IG-21 was 3 cm-4 cm, while median weight at term differed by 200 g. The Lithuanian median weight at term was higher than in IG-21 by a full centile channel width, while the median length at term was higher by two channel widths. Based on the regional reference, the prevalence rates of SGA/LGA were 9.7%/10.1% for boys and 10.1%/9.9% for girls, close to the nominal 10%. Conversely, based on IG-21, the prevalence of SGA in boys/girls was less than half (4.1%/4.4%), while the prevalence of LGA was double (20.7%/19.1%).

Discussion

Regional population-based neonatal references represent Lithuanian neonatal weight and length much more accurately than the global standard IG-21 which provides the prevalence rates for SGA/LGA that differ from the true values by a factor of two.

Parity-Adjusted Term Neonatal Growth Chart Modifies Neonatal Morbidity and Mortality Risk Stratification

Objective: To investigate the impact of parity-customized versus population-based birth weight charts on the identification of neonatal risk for adverse outcomes in small (SGA) or large for gestational age (LGA) infants compared to appropriate for gestational age (AGA) infants. Study design: Observational, retrospective, cohort study based on electronic medical birth records at a single center between 2006 and 2017. Neonates were categorized by birth weight (BW) as SGA, LGA, or AGA, with the 10th and 90th centiles as boundaries for AGA in a standard population-based model adjusted for gestational age and gender only (POP) and a customized model adjusted for gestational age, gender, and parity (CUST). Neonates defined as SGA or LGA by one standard and not overlapping the other, are SGA/LGA CUST/POP ONLY. Analyses used a reference group of BW between the 25th and 75th centile for the population. Results: Overall 132,815 singleton, live, term neonates born to mothers with uncomplicated pregnancies were included. The customized model identified 53% more neonates as SGA-CUST ONLY who had significantly higher rates of morbidity and mortality compared to the reference group (OR = 1.33 95% CI [1.16−1.53]; p < 0.0001). Neonates defined as LGA by the customized model (LGA-CUST) and AGA by the population-based model LGA-CUST ONLY had a significantly higher risk for morbidity compared to the reference (OR = 1.36 95% CI [1.09−1.71]; p = 0.007) or the LGA POP group. Neonatal mortality only occurred in the SGA and AGA groups. Conclusions: The application of a parity-customized only birth weight chart in a population of singleton, term neonates is a simple platform to better identify birth weight related neonatal risk for morbidity and mortality.

Development of the Birthweight Appropriateness Quotient: A New Measure of Infant's Size

INTRODUCTION

The customised birthweight model can be used to improve detection of babies that may be at risk of adverse outcomes associated with abnormal growth, however it is currently used in conjunction with either an intrauterine growth standard or the individualised birthweight ratio (IBR), both of which have significant methodological flaws. Our aim was to investigate the statistical validity of the IBR and attempt to develop a new measurement to represent the appropriateness of an infant's size at birth that will support clinicians in identifying infants requiring further attention.

METHODS

Routinely collected hospital maternity and neonatal data on singleton, term births from a tertiary Australian hospital were extracted for the time period 1998-2009. The relationships between birthweight, customised birthweight and IBR are investigated using correlation, regression analysis and division of births into groups of < 2500 g, 2500-4000 g and > 4000 g. A new measure, the Birthweight Appropriateness Quotient (BAQ), is developed. The utility of the BAQ is compared with IBR and birthweight to identify infants with a composite neonatal morbidity outcome.

RESULTS

Statistical flaws with the IBR due to significant correlation between birthweight and customised birthweight and a heterogenous relationship between these two measurements across the range of birthweight are present. BAQ is uncorrelated with birthweight. Comparison of BAQ and IBR as indicators of adverse neonatal outcome demonstrates that BAQ identifies babies at risk due to their small size and those babies at risk due to inappropriate size.

CONCLUSIONS FOR PRACTICE

BAQ is a customised measurement of an infant's size free of the statistical flaws experienced by the IBR with the ability to identify at-risk infants.

Introduction of a customised growth chart protocol increased detection of small for gestational age pregnancies in a tertiary Melbourne hospital

BACKGROUND

Growth charts customised for maternal height, weight, ethnicity and parity have been proposed as more effective at detecting infants who are small for gestational age (SGA) than routine screening with symphysio-fundal height measurement alone. Our non-randomised, prospective cohort study assessed antenatal SGA detection rates in a general maternity cohort following the introduction of the Perinatal Institute's Growth Assessment Protocol (GAP) program (consisting of customised growth chart software for plotting symphysio-fundal height, staff training and serial auditing).

METHODS

The GAP program was implemented into the routine antenatal schedule of 882 women who delivered at The Royal Women's Hospital, Melbourne, during our study period. SGA detection was compared to 936 women from the same team who delivered prior to the intervention. Secondary outcomes assessed were infant gestation at birth and method of delivery, neonatal Apgar scores and admission to the Neonatal Intensive and Special Care nursery (NISC).

RESULTS

Identification of SGA infants increased from 21% to 41% with the introduction of the GAP program (OR 2.6, 95% CI 1.3-4.9, P < 0.05). This was not associated with an increase in false-positive rates. Following the introduction of the GAP Program, SGA babies were more likely to be born by vaginal delivery (OR 2.7; 95% CI 1.4-5.1, P < 0.005). There was no overall increase in the induction of labour or caesarean delivery rates. Overall rates of admission to NISC were reduced.

CONCLUSIONS

In our increasingly culturally heterogenous society, the use of the GAP program is a safe and potentially more sensitive tool for detecting in utero growth restriction.

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.

Prevalence of small-for-gestational-age and its mortality risk varies by choice of birth-weight-for-gestation reference population

Background

We use data from rural Nepal and South India to compare the prevalence of small-for-gestational-age (SGA) and neonatal mortality risk associated with SGA using different birth-weight-for-gestation reference populations.

Methods

We identified 46 reference populations in low-, middle-, and high-income countries, of which 26 met the inclusion criteria of being commonly cited and having numeric 10^th percentile cut points published. Those reference populations were then applied to populations from two community-based studies to determine SGA prevalence and its relative risk of neonatal mortality.

Results

The prevalence of SGA ranged from 10.5% to 72.5% in Nepal, and 12.0% to 78.4% in India, depending on the reference population. Females had higher rates of SGA than males using reference populations that were not sex specific. SGA prevalence was lowest when using reference populations from low-income countries. Infants who were both preterm and SGA had much higher mortality risk than those who were term and appropriate-for-gestational-age. Risk ratios for those who are both preterm and SGA ranged from 7.34–17.98 in Nepal and 5.29–11.98 in India, depending on the reference population.

Conclusions

These results demonstrate the value of a common birth-weight-for-gestation reference population that will facilitate comparisons of SGA prevalence and mortality risk across research studies.

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.