Fetal growth restriction and small for gestational age as predictors of neonatal morbidity: which growth nomogram to use?

BACKGROUND

Fetal growth nomograms were developed to screen for fetal growth restriction and guide clinical care to improve perinatal outcomes; however, existing literature remains inconclusive regarding which nomogram is the gold standard.

OBJECTIVE

This study aimed to compare the ability of 4 commonly used nomograms (Hadlock, International Fetal and Newborn Growth Consortium for the 21st Century, Eunice Kennedy Shriver National Institute of Child Health and Human Development-unified standard, and World Health Organization fetal growth charts) and 1 institution-specific reference to predict small for gestational age and poor neonatal outcomes.

STUDY DESIGN

This was a retrospective cohort study of all nonanomalous singleton pregnancies undergoing ultrasound at ≥20 weeks of gestation between 2013 and 2020 and delivering at a single academic center. Using random selection methods, the study sample was restricted to 1 pregnancy per patient and 1 ultrasound per pregnancy completed at ≥22 weeks of gestation. Fetal biometry data were used to calculate estimated fetal weight and percentiles according to the aforementioned 5 nomograms. Maternal and neonatal data were extracted from electronic medical records. Logistic regression was used to estimate the association between estimated fetal weight of <10th and <3rd percentiles compared with estimated fetal weight of 10th to 90th percentile as the reference group for small for gestational age and the neonatal composite outcomes (perinatal mortality, hypoxic-ischemic encephalopathy or seizures, respiratory morbidity, intraventricular hemorrhage, necrotizing enterocolitis, hyperbilirubinemia or hypoglycemia requiring neonatal intensive care unit admission, and retinopathy of prematurity). Receiver operating characteristic curve contrast estimation (primary analysis) and test characteristics were calculated for all nomograms and the prediction of small for gestational age and the neonatal composite outcomes. We restricted the sample to ultrasounds performed within 28 days of delivery; moreover, similar analyses were completed to assess the prediction of small for gestational age and neonatal composite outcomes.

RESULTS

Among 10,045 participants, the proportion of fetuses classified as <10th percentile varied across nomograms from 4.9% to 9.7%. Fetuses with an estimated fetal weight of <10th percentile had an increased risk of small for gestational age (odds ratio, 9.9 [95% confidence interval, 8.5-11.5] to 12.8 [95% confidence interval, 10.9-15.0]). In addition, the estimated fetal weight of <10th and <3rd percentile was associated with increased risk of the neonatal composite outcome (odds ratio, 2.4 [95% confidence interval, 2.0-2.8] to 3.5 [95% confidence interval, 2.9-4.3] and 5.7 [95% confidence interval, 4.5-7.2] to 8.8 [95% confidence interval, 6.6-11.8], respectively). The prediction of small for gestational age with an estimated fetal weight of <10th percentile had a positive likelihood ratio of 6.3 to 8.5 and an area under the curve of 0.62 to 0.67. Similarly, the prediction of the neonatal composite outcome with an estimated fetal weight of <10th percentile had a positive likelihood ratio of 2.1 to 3.1 and an area under the curve of 0.55 to 0.57. When analyses were restricted to ultrasound within 4 weeks of delivery, among fetuses with an estimated fetal weight of <10th percentile, the risk of small for gestational age increased across all nomograms (odds ratio, 16.7 [95% confidence interval, 12.6-22.3] to 25.1 [95% confidence interval, 17.0-37.0]), and prediction improved (positive likelihood ratio, 8.3-15.0; area under the curve, 0.69-0.75). Similarly, the risk of neonatal composite outcome increased (odds ratio, 3.2 [95% confidence interval, 2.4-4.2] to 5.2 [95% confidence interval, 3.8-7.2]), and prediction marginally improved (positive likelihood ratio, 2.4-4.1; area under the curve, 0.60-0.62). Importantly, the risk of both being small for gestational age and having the neonatal composite outcome further increased (odds ratio, 21.4 [95% confidence interval, 13.6-33.6] to 28.7 (95% confidence interval, 18.6-44.3]), and the prediction of concurrent small for gestational age and neonatal composite outcome greatly improved (positive likelihood ratio, 6.0-10.0; area under the curve, 0.80-0.83).

CONCLUSION

In this large cohort, Hadlock, recent fetal growth nomograms, and a local population-derived fetal growth reference performed comparably in the prediction of small for gestational age and neonatal composite outcomes.

The Danish newborn standard and the International Fetal and Newborn Growth Consortium for the 21st Century newborn standard: a nationwide register-based cohort study

BACKGROUND

It is a matter of debate whether 1 universal standard, such as the International Fetal and Newborn Growth Consortium for the 21st Century standard, can be applied to all populations.

OBJECTIVE

The primary objective was to establish a Danish newborn standard based on the criteria of the International Fetal and Newborn Growth Consortium for the 21st Century standard to compare the percentiles of these 2 standards. A secondary objective was to compare the prevalence and risk of fetal and neonatal deaths related to small for gestational age defined by the 2 standards when used in the Danish reference population.

STUDY DESIGN

This was a register-based nationwide cohort study. The Danish reference population included 375,318 singletons born at 33 to 42 weeks of gestation in Denmark between January 1, 2008, and December 31, 2015. The Danish standard cohort included 37,811 newborns who fulfilled the criteria of the International Fetal and Newborn Growth Consortium for the 21st Century standard. Birthweight percentiles were estimated using smoothed quantiles for each gestational week. The outcomes included birthweight percentiles, small for gestational age (defined as a birthweight of 3rd percentile), and adverse outcomes (defined as either fetal or neonatal death).

RESULTS

At all gestational ages, the Danish standard median birthweights at term were higher than the International Fetal and Newborn Growth Consortium for the 21st Century standard median birthweights: 295g for females and 320 g for males. Therefore, the estimates of the prevalence rate of small for gestational age within the entire population were different: 3.9% (n=14,698) using the Danish standard vs 0.7% (n=2640) using the International Fetal and Newborn Growth Consortium for the 21st Century standard. Accordingly, the relative risk of fetal and neonatal deaths among small-for-gestational-age fetuses differed by SGA status defined by the different standards (4.4 [Danish standard] vs 9.6 [International Fetal and Newborn Growth Consortium for the 21st Century standard]).

CONCLUSION

Our finding did not support the hypothesis that 1 universal standard birthweight curve can be applied to all populations.