Unified standard for fetal growth: the Eunice Kennedy Shriver National Institute of Child Health and Human Development Fetal Growth Studies

Genetic disorders and their association with morbidity and mortality in early preterm small for gestational age infants

BACKGROUND

Early preterm (<34 weeks of gestation) small for gestational age infants (<10th percentile birth weight for sex and gestational age) experience high rates of morbidity and mortality, the causes of which are poorly understood. Mounting evidence suggests that genetic disorders contribute. Scarce data exist regarding the prevalence of genetic disorders and their contribution to morbidity and mortality.

OBJECTIVE

This study aimed to determine the proportion of genetic disorders in early preterm small for gestational age infants (with and without congenital anomalies) compared to early preterm appropriate for gestational age infants and the association of genetic disorders with morbidity or mortality.

STUDY DESIGN

This is a retrospective cohort study of infants delivered at 23 and 0/7 to 33 and 6/7 weeks of gestation from 2000 to 2020 from the Pediatrix Clinical Data Warehouse. Data included diagnosed genetic disorders and congenital anomalies, baseline characteristics, and morbidity or mortality. We excluded cases of death in the delivery room before neonatal intensive care unit admission, multiple gestations, and cases transferred after birth or before death or discharge.

RESULTS

We identified 223,431 early preterm infants, including 21,180 small for gestational age. Genetic disorders were present in 441 (2.3%) of small for gestational age infants without congenital anomalies, in 194 (10.8%) of small for gestational age infants with congenital anomalies, and in 304 (4.5%) of small for gestational age infants that experienced morbidity or mortality (with or without congenital anomalies). Trisomies 13, 18, and 21 were the most prevalent genetic disorders in these groups, together accounting for 145 small for gestational age infants without congenital anomalies, 117 small for gestational age infants with congenital anomalies, and 166 small for gestational age infants with morbidity or mortality (with or without congenital anomalies). Less prevalent genetic disorders consisted of other aneuploidy (45, X and 47, XXY), copy number variants (13q14 deletion syndrome, cri du chat syndrome, DiGeorge syndrome), and single gene disorders (cystic fibrosis, Fanconi anemia, glucose-6-phosphate dehydrogenase deficiency, hemophilia, hypophosphatasia, sickle cell disease, and thalassemia). Comparatively, genetic disorders were found in 1792 (1.0%) appropriate for gestational age infants without congenital anomalies, in 572 (5.8%) appropriate for gestational age infants with congenital anomalies, and 809 (2.0%) appropriate for gestational age infants that experienced morbidity or mortality (with or without congenital anomalies). Genetic disorders were associated with an adjusted odds ratio (95% confidence interval) of 2.10 (1.89-2.33) of isolated small for gestational age and 12.84 (11.47-14.35) of small for gestational age accompanied by congenital anomalies. Genetic disorders were associated with an adjusted odds ratio of 2.24 (1.83-2.74) of morbidity or mortality.

CONCLUSION

These findings suggest that genetic disorders are more prevalent in early preterm small for gestational age infants, particularly those with congenital anomalies. These findings also suggest that genetic disorders are associated with increased morbidity and mortality. These associations were primarily driven by trisomies 13, 18, and 21. Genetic diagnoses in this cohort were made through routine clinical care, principally via karyotype, chromosomal microarray, and single gene testing. These findings support evolving clinical guidelines for genetic testing of small for gestational age infants. Our study is limited due to the lack of prospective, genome-wide testing.

Fetal Body Composition in Twins and Singletons

Importance

An emerging paradigm attributes third-trimester fetal growth deceleration in uncomplicated twin pregnancies to an evolutionary adaptive process. Evaluating longitudinal fetal soft-tissue development may provide important insights into differential fetal growth trajectories between twins and singletons.

Objective

To compare twin vs singleton lean and fat tissue growth across pregnancy.

Design, Setting, and Participants

Prospective cohort study of dichorionic twins and singletons with serial ultrasound scans to chart fetal growth (2009-2013) and collect fetal volume data to measure fat and lean tissue (2015-2019) in 12 US clinical centers. Participants were individuals with singleton (n = 2802 enrolled) and twin (n = 171 pairs enrolled) pregnancies who generally had no chronic disease. Data analysis was performed from September 2023 to June 2024.

Exposure

Twin status.

Main Outcomes and Measures

Abdominal area, maximum abdominal subcutaneous tissue thickness, fractional thigh volume, fractional lean thigh volume, fractional fat thigh volume, midthigh area (including lean and fat components), ratio of fractional fat thigh volume to fractional thigh volume, and ratio of midthigh fat area to midthigh area, measured up to 6 times between 15 and 37 weeks' gestation.

Results

Analyses included 315 twin and 2604 singleton fetuses. The mean (SD) maternal age at delivery was 31.3 (6.1) years for twins and 28.2 (5.5) years for singletons, with a mean (SD) gestational age at delivery of 35.2 (4.2) weeks for twins and 39.2 (1.7) weeks for singletons. Mean twin abdominal measurements were significantly smaller than those of singletons between 25 and 37 weeks' gestation for area (difference at 25 weeks, -48.6 [95% CI, -102.2 to -5.1] mm2; difference at 37 weeks, -480.5 [95% CI, -677.2 to -283.5] mm2) and between 27 and 37 weeks for maximum abdominal subcutaneous tissue thickness (difference at 27 weeks, -0.13 [95% CI, -0.24 to -0.02] mm; difference at 37 weeks, -0.40 [95% CI, -0.68 to -0.13] mm). Beginning at 15 weeks, fractional thigh volumes were significantly smaller for twins (mean fractional thigh volume difference, -0.11 [95% CI, -0.16 to -0.07] cm3; mean fractional fat thigh volume difference, -0.08 [95% CI,-0.12 to -0.05] cm3) relative to singletons, persisting through 37 weeks (mean fractional thigh volume difference, -7.55 [95% CI, -11.76 to -3.34] cm3; mean fractional fat thigh volume difference, -5.60 [95% CI, -8.37 to -2.82] cm3). Mean fractional lean thigh volume was significantly smaller for twins at 15 to 16 and 23 to 36 weeks. For the ratio of fractional fat thigh volume to fractional thigh volume, twins had a 2.7% to 4.2% smaller fat percentage between 15 and 37 weeks compared with singletons.

Conclusions and Relevance

Twins had proportionally less fat tissue accumulation in utero compared with singletons as early as 15 weeks' gestation, when competition for nutritional resources was low. Persistent findings of smaller twin sizes and less fat accumulation across pregnancy support the concept of an early evolutionary adaptive process in otherwise uncomplicated dichorionic twin growth.

Revisiting the Hadlock 1991 population reference for estimated fetal weight

OBJECTIVE

The most widely used population reference standard for fetal growth assessment in the United States is the Hadlock 1991 population reference. However, we detected discrepancies in the Hadlock 1991 publication between its stated methodology and its presentation of critical point values. This study investigates these discrepancies and their potential effects on clinical practice and research.

STUDY DESIGN

The Hadlock 1991 table describing a fetal weight standard was recalculated from the Hadlock 1991 formula as printed in the body of the text. A difference was observed between the equation results and the table as published in the 1991 manuscript. These 2 methods for assessing estimated fetal weight percentiles were retrospectively applied to a cohort of all singleton growth ultrasounds performed at our institution since 2015. We also collected a sample of manuscripts in the literature that reference Hadlock 1991 to determine if methodology varied among previously published reports.

RESULTS

The Hadlock 1991 equation does not produce the same critical point values for estimated fetal weight as the table presented in the manuscript. In our database of 176,060 ultrasound encounters for growth in singleton fetuses (78,660 patients), the Hadlock table, as compared to the Hadlock equation, would have resulted in underdiagnosis of fetal growth restriction in 5.1% (4009/78,660) of patients. Manuscripts that compared Hadlock 1991 to other growth standards tended to favor Hadlock 1991 if the equation was used, and disfavor it if the table was used.

CONCLUSION

The Hadlock 1991 regression equation presented in the manuscript and the table are not the same. The table underdiagnoses fetal growth restriction and, potentially, impacts clinical intervention for fetuses at risk for growth abnormality. Inconsistencies in previous studies on the detection of fetal growth restriction using Hadlock 1991 may be attributed to these discrepancies. If increased detection of fetal growth restriction is desired, then Interpolation of the Hadlock 1991 table should be avoided and the equation preferred instead. Additional validation of these findings is required to ascertain clinical significance.

Expanding the Estimated Fetal Weight Definition of Growth Restriction by Adding Small Abdominal Circumference: Prediction of Neonatal Morbidity

OBJECTIVE

The Society for Maternal-Fetal Medicine's (SMFM) diagnostic criteria for fetal growth restriction (FGR) recently added abdominal circumference (AC) <10th percentile to estimated fetal weight (EFW) <10th percentile; however, its prediction of neonatal morbidity is unknown. Our objective was to compare the two definitions for their prediction of composite neonatal morbidity.

METHODS

Secondary analysis of the Fetal Growth Study-Singletons, 2009-2013. The last ultrasound (mean 36.9 ± 2.3 weeks) was included from non-anomalous fetuses. Composite neonatal morbidity was the primary outcome: metabolic acidosis, neonatal intensive care unit stay >3 days, significant respiratory morbidities, seizures, hyperbilirubinemia requiring exchange transfusion, intrapartum aspiration, necrotizing enterocolitis, hypoglycemia, hypoxic ischemic encephalopathy, periventricular leukomalacia, sepsis, retinopathy of prematurity, or neonatal death. The secondary outcome was small for gestational age (SGA). Logistic regression modeled the association of each FGR definition with outcomes, and receiver operating characteristic area under the curve (AUC) assessed predictive ability.

RESULTS

Of 2400 eligible individuals, 135 (5.6%) neonates had composite neonatal morbidity, and 245 (10%) were SGA. At the last ultrasound, 181 (7.5%) had FGR based on EFW alone (original definition) and 215 (9.0%) had FGR based on a small EFW or AC (expanded definition) (P < .0001). Both definitions had poor discrimination for composite neonatal morbidity (original: AUC 0.52, 95% confidence interval [CI] 0.49-0.54; expanded: AUC 0.51, 95% CI, 0.48-0.54). Both had acceptable discrimination of SGA (original: AUC 0.70, 95% CI 0.67-0.73; expanded: AUC 0.71, 95% CI 0.68-0.75).

CONCLUSIONS

Adding AC <10th percentile to the EFW <10th percentile definition of FGR significantly increased the incidence of FGR but did not improve the prediction of neonatal morbidity in a low-risk population. The SMFM guideline for FGR should be adopted with caution.

Multiethnic growth standards for fetal body composition and organ volumes derived from 3D ultrasonography

BACKGROUND

A major goal of contemporary obstetrical practice is to optimize fetal growth and development throughout pregnancy. To date, fetal growth during prenatal care is assessed by performing ultrasonographic measurement of 2-dimensional fetal biometry to calculate an estimated fetal weight. Our group previously established 2-dimensional fetal growth standards using sonographic data from a large cohort with multiple sonograms. A separate objective of that investigation involved the collection of fetal volumes from the same cohort.

OBJECTIVE

The Fetal 3D Study was designed to establish standards for fetal soft tissue and organ volume measurements by 3-dimensional ultrasonography and compare growth trajectories with conventional 2-dimensional measures where applicable.

STUDY DESIGN

The National Institute of Child Health and Human Development Fetal 3D Study included research-quality images of singletons collected in a prospective, racially and ethnically diverse, low-risk cohort of pregnant individuals at 12 U.S. sites, with up to 5 scans per fetus (N=1730 fetuses). Abdominal subcutaneous tissue thickness was measured from 2-dimensional images and fetal limb soft tissue parameters extracted from 3-dimensional multiplanar views. Cerebellar, lung, liver, and kidney volumes were measured using virtual organ computer aided analysis. Fractional arm and thigh total volumes, and fractional lean limb volumes were measured, with fractional limb fat volume calculated by subtracting lean from total. For each measure, weighted curves (fifth, 50th, 95th percentiles) were derived from 15 to 41 weeks' using linear mixed models for repeated measures with cubic splines.

RESULTS

Subcutaneous thickness of the abdomen, arm, and thigh increased linearly, with slight acceleration around 27 to 29 weeks. Fractional volumes of the arm, thigh, and lean limb volumes increased along a quadratic curvature, with acceleration around 29 to 30 weeks. In contrast, growth patterns for 2-dimensional humerus and femur lengths demonstrated a logarithmic shape, with fastest growth in the second trimester. The mid-arm area curve was similar in shape to fractional arm volume, with an acceleration around 30 weeks, whereas the curve for the lean arm area was more gradual. The abdominal area curve was similar to the mid-arm area curve with an acceleration around 29 weeks. The mid-thigh and lean area curves differed from the arm areas by exhibiting a deceleration at 39 weeks. The growth curves for the mid-arm and thigh circumferences were more linear. Cerebellar 2-dimensional diameter increased linearly, whereas cerebellar 3-dimensional volume growth gradually accelerated until 32 weeks followed by a more linear growth. Lung, kidney, and liver volumes all demonstrated gradual early growth followed by a linear acceleration beginning at 25 weeks for lungs, 26 to 27 weeks for kidneys, and 29 weeks for liver.

CONCLUSION

Growth patterns and timing of maximal growth for 3-dimensional lean and fat measures, limb and organ volumes differed from patterns revealed by traditional 2-dimensional growth measures, suggesting these parameters reflect unique facets of fetal growth. Growth in these three-dimensional measures may be altered by genetic, nutritional, metabolic, or environmental influences and pregnancy complications, in ways not identifiable using corresponding 2-dimensional measures. Further investigation into the relationships of these 3-dimensional standards to abnormal fetal growth, adverse perinatal outcomes, and health status in postnatal life is warranted.

Relationship between gestational weight gain with fetal body composition and organ volumes in the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Dimensional Study: a prospective pregnancy cohort

BACKGROUND

Inadequate and excessive gestational weight gain (GWG) are associated with increased risk of newborn small- and large-for-gestational-age, respectively, and future offspring adiposity. However, the relationship between GWG and three-dimensional (3D) measures of fetal body composition and organ volumes, which may provide greater insight into fetal growth via measurement of soft tissue, remains unknown.

OBJECTIVES

The objective of this study was to examine the relationship between trimester-specific GWG and 3D fetal body composition and organ volume measurements.

METHODS

In a diverse, US prospective pregnancy cohort, trimester-specific GWG was calculated as difference between maternal weight at beginning and end of each trimester, and categorized as inadequate, adequate, or excessive, per 2009 Institute of Medicine (IOM) guidelines. Up to five 3D ultrasound scans were completed across gestation, from which fetal body composition and organ volume measurements were obtained (n = 2675 pregnancies). The associations between trimester-specific GWG categories and 3D fetal body composition and organ volumes were assessed at 15, 29, and 39 weeks.

RESULTS

Excessive compared with adequate GWG, in first and second trimesters was associated with larger abdominal circumference (n = 2430; 1st trimester: 1.29 cm, 95% CI: 0.74, 1.84; 2nd trimester: 2.98 cm, 95% CI: 1.62, 4.34) and abdominal area (n = 2401; 1st trimester: 22.04 mm2, 95% CI: 0.48, 43.60; 2nd trimester: 162.34 mm2, 95% CI: 76.25, 248.44), whereas excessive GWG in the first trimester was associated with larger arm subcutaneous tissue thickness (n = 1921; 0.01 cm, 95% CI: 0.00, 0.01). There was a trend toward increased fetal arm, thigh, kidney, and liver volumes and abdominal subcutaneous tissue, although differences did not reach the level of statistical significance for these structures.

CONCLUSIONS

Excessive GWG was associated with greater fetal size primarily manifested by a pattern of fat accumulation across the fetal arm and abdomen. Future studies should examine whether these fetal changes have functional implications for childhood adiposity and metabolic dysfunction. This trial was registered at https://clinicaltrials.gov as NCT00912132 and NCT03266198.

Comparing population-based fetal growth standards in a US cohort

BACKGROUND

No fetal growth standard is currently endorsed for universal use in the United States. Newer standards improve upon the methodologic limitations of older studies; however, before adopting into practice, it is important to know how recent standards perform at identifying fetal undergrowth or overgrowth and at predicting subsequent neonatal morbidity or mortality in US populations.

OBJECTIVE

To compare classification of estimated fetal weight that is <5th or 10th percentile or >90th percentile by 6 population-based fetal growth standards and the ability of these standards to predict a composite of neonatal morbidity and mortality.

STUDY DESIGN

We used data from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be cohort, which recruited nulliparous women in the first trimester at 8 US clinical centers (2010-2014). Estimated fetal weight was obtained from ultrasounds at 16 to 21 and 22 to 29 weeks of gestation (N=9534 women). We calculated rates of fetal growth restriction (estimated fetal weight <5th and 10th percentiles; fetal growth restriction<5 and fetal growth restriction<10) and estimated fetal weight >90th percentile (estimated fetal weight>90) from 3 large prospective fetal growth cohorts with similar rigorous methodologies: INTERGROWTH-21, World Health Organization-sex-specific and combined, Eunice Kennedy Shriver National Institute of Child Health and Human Development race-ethnic-specific and unified, and the historic Hadlock reference. To determine whether differential classification of fetal growth restriction or estimated fetal weight >90 among standards was clinically meaningful, we then compared area under the curve and sensitivity of each standard to predict small for gestational age or large for gestational age at birth, composite perinatal morbidity and mortality alone, and small for gestational age or large for gestational age with composite perinatal morbidity and mortality.

RESULTS

The standards classified different proportions of fetal growth restriction and estimated fetal weight>90 for ultrasounds at 16 to 21 (visit 2) and 22 to 29 (visit 3) weeks of gestation. At visit 2, the Eunice Kennedy Shriver National Institute of Child Health and Human Development race-ethnic-specific, World Health Organization sex-specific and World Health Organization-combined identified similar rates of fetal growth restriction<10 (8.4%-8.5%) with the other 2 having lower rates, whereas Eunice Kennedy Shriver National Institute of Child Health and Human Development race-ethnic-specific identified the highest rate of fetal growth restriction<5 (5.0%) compared with the other references. At visit 3, World Health Organization sex-specific classified 9.2% of fetuses as fetal growth restriction<10, whereas the other 5 classified a lower proportion as follows: World Health Organization-combined (8.4%), Eunice Kennedy Shriver National Institute of Child Health and Human Development race-ethnic-specific (7.7%), INTERGROWTH (6.2%), Hadlock (6.1%), and Eunice Kennedy Shriver National Institute of Child Health and Human Development unified (5.1%). INTERGROWTH classified the highest (21.3%) as estimated fetal weight>90 whereas Hadlock classified the lowest (8.3%). When predicting composite perinatal morbidity and mortality in the setting of early-onset fetal growth restriction, World Health Organization had the highest area under the curve of 0.53 (95% confidence interval, 0.51-0.53) for fetal growth restriction<10 at 22 to 29 weeks of gestation, but the areas under the curve were similar among standards (0.52). Sensitivity was generally low across standards (22.7%-29.1%). When predicting small for gestational age birthweight with composite neonatal morbidity or mortality, for fetal growth restriction<10 at 22 to 29 weeks of gestation, World Health Organization sex-specific had the highest area under the curve (0.64; 95% confidence interval, 0.60-0.67) and INTERGROWTH had the lowest (area under the curve=0.58; 95% confidence interval 0.55-0.62), though all standards had low sensitivity (7.0%-9.6%).

CONCLUSION

Despite classifying different proportions of fetuses as fetal growth restriction or estimated fetal weight>90, all standards performed similarly in predicting perinatal morbidity and mortality. Classification of different percentages of fetuses as fetal growth restriction or estimated fetal weight>90 among references may have clinical implications in the management of pregnancies, such as increased antenatal monitoring for fetal growth restriction or cesarean delivery for suspected large for gestational age. Our findings highlight the importance of knowing how standards perform in local populations, but more research is needed to determine if any standard performs better at identifying the risk of morbidity or mortality.

Quantitative Approach to Quality Review of Prenatal Ultrasound Examinations: Fetal Biometry

Background/Objectives: To evaluate the quality of an ultrasound practice, both large-scale and focused audits are recommended by professional organizations, but such audits can be time-consuming, inefficient, and expensive. Our objective was to develop a time-efficient, quantitative, objective, large-scale method to evaluate fetal biometry measurements for an entire practice, combined with a process for focused image review for personnel whose measurements are outliers. Methods: Ultrasound exam data for a full year are exported from commercial ultrasound reporting software to a statistical package. Fetal biometry measurements are converted to z-scores to standardize across gestational ages. For a large-scale audit, sonographer mean z-scores are compared using analysis of variance (ANOVA) with Scheffe multiple comparisons test. A focused image review is performed on a random sample of exams for sonographers whose mean z-scores differ significantly from the practice mean. A similar large-scale audit is performed, comparing physician mean z-scores. Results: Using fetal abdominal circumference measurements as an example, significant differences between sonographer mean z-scores are readily identified by the ANOVA and Scheffe test. A method is described for the blinded image audit of sonographers with outlier mean z-scores. Examples are also given for the identification and interpretation of several types of systematic errors that are unlikely to be detectable by image review, including z-scores with large or small standard deviations and physicians with outlier mean z-scores. Conclusions: The large-scale quantitative analysis provides an overview of the biometry measurements of all the sonographers and physicians in a practice, so that image audits can be focused on those whose measurements are outliers. The analysis takes little time to perform after initial development and avoids the time, complexity, and expense of auditing providers whose measurements fall within the expected range. We encourage commercial software developers to include tools in their ultrasound reporting software to facilitate such quantitative reviews.

Selection of Standards for Sonographic Fetal Head Circumference by Use of z-Scores

OBJECTIVE

This study aimed to evaluate which of five established norms should be used for sonographic assessment of fetal head circumference (HC).

STUDY DESIGN

Cross-sectional study using pooled data from four maternal-fetal medicine practices. Inclusion criteria were singleton fetus, gestational age 220/7 to 396/7 weeks, biometry measured, and fetal cardiac activity present. Five norms of HC were studied: Jeanty et al, Hadlock et al, the INTERGROWTH-21st Project (IG-21st), the World Health Organization Fetal Growth Curves (WHO), and the National Institutes of Child Health and Human Development Fetal Growth Studies unified standard (NICHD-U). The fit of our HC measurements to each norm was assessed by these criteria: mean z-score close to 0, standard deviation (SD) of z close to 1, low Kolmogorov-Smirnov D-statistic, high Youden J-statistic, close to 10% of exams >90th percentile, close to 10% of exams <10th percentile, and close to 2.28% of exams >2 SD below the mean.

RESULTS

In 23,565 ultrasound exams, our HC measurements had the best fit to the WHO standard (mean z-score 0.10, SD of z = 1.01, D-statistic <0.01, J-statistic 0.83-0.94). The SD of the Jeanty reference was much larger than all the other norms and our measurements, resulting in underdiagnosis of abnormal HC. The means of the IG-21st and NICHD-U standards were smaller than the other norms and our measurements, resulting in underdiagnosis of small HC. The means of the Hadlock reference were larger than all the other norms and our measurements, resulting in overdiagnosis of small HC. Restricting the analysis to a low-risk subgroup of 4,423 exams without risk factors for large- or small-for-gestational age produced similar results.

CONCLUSION

The WHO standard is likely best for diagnosis of abnormal HC. The Jeanty (Chervenak) reference suggested by the Society for Maternal-Fetal Medicine had poor sensitivity for microcephaly screening.

KEY POINTS

· There are >30 norms for fetal HC.. · It is unknown which norm should be used.. · The WHO standard fits our data best.. · The Chervenak reference is not sensitive for microcephaly..

Selection of Standards for Sonographic Fetal Femur Length by Use of z-scores

OBJECTIVES

This study aimed to evaluate which of four established norms should be used for sonographic assessment of fetal femur length (FL).

STUDY DESIGN

Cross-sectional study using pooled data from four maternal-fetal medicine practices. Inclusion criteria were singleton fetus, gestational age (GA) 220/7 to 396/7 weeks, biometry measured, and fetal cardiac activity present. Four norms of FL were studied: Hadlock et al, the INTERGROWTH-21st Project (IG-21st), the World Health Organization Fetal Growth Curves (WHO), and the National Institutes of Child Health and Human Development Fetal Growth Studies, unified standard (NICHD-U). The fit of our FL measurements to each norm was assessed by these criteria: mean z-score close to 0, standard deviation (SD) of z close to 1, Kolmogorov-Smirnov D-statistic close to zero, Youden J-statistic close to 1, approximately 5% of exams <5th percentile, and approximately 5% of exams >95th percentile.

RESULTS

In 26,177 ultrasound exams, our FL measurements had the best fit to the WHO standard (mean z-score 0.15, SD of z 1.02, D-statistic <0.01, J-statistic 0.95, 3.4% of exams <5th percentile, 7.0% of exams >95th percentile). The mean of the IG-21st standard was smaller than the other norms and smaller than our measurements, resulting in underdiagnosis of short FL. The mean of the Hadlock reference was larger than the other norms and larger than our measurements, resulting in overdiagnosis of short FL. The SD of the NICHD-U standard was larger than the other norms and larger than our observations, resulting in underdiagnosis of both short and long FL. Restricting the analysis to a subgroup of 7,144 low-risk patients without risk factors for large- or small-for- GA produced similar results.

CONCLUSION

Of the norms studied, the WHO standard is likely best for diagnosis of abnormal FL.

KEY POINTS

· There are >30 norms for fetal FL.. · It is unknown which norm should be used.. · Our data fit the World Health Organization standard better than the other norms..

The NICHD Fetal 3D Study: A Pregnancy Cohort Study of Fetal Body Composition and Volumes

There's a paucity of robust normal fractional limb and organ volume standards from a large and diverse ethnic population. The Fetal 3D Study was designed to develop research and clinical applications for fetal soft tissue and organ volume assessment. The NICHD Fetal Growth Studies (2009-2013) collected 2D and 3D fetal volumes. In the Fetal 3D Study (2015-2019), sonographers performed longitudinal 2D and 3D measurements for specific fetal anatomical structures in research ultrasounds of singletons and dichorionic twins. The primary aim was to establish standards for fetal body composition and organ volumes, overall and by maternal race/ethnicity, and determine whether these standards vary for twins versus singletons. We describe the study design, methods, and details about reviewer training. Basic characteristics of this cohort, with their corresponding distributions of fetal 3D measurements by anatomical structure, are summarized. This investigation is responsive to critical data gaps in understanding serial changes in fetal subcutaneous fat, lean body mass, and organ volume in association with pregnancy complications. In the future, this cohort can answer critical questions regarding the potential influence of maternal characteristics, lifestyle factors, nutrition, and biomarker and chemical data on longitudinal measures of fetal subcutaneous fat, lean body mass, and organ volumes.

Periconceptional Dietary Patterns and Adverse Pregnancy and Birth Outcomes

BACKGROUND

The periconceptional period is a critical window for the origins of adverse pregnancy and birth outcomes, yet little is known about the dietary patterns that promote perinatal health.

OBJECTIVE

We used machine learning methods to determine the effect of periconceptional dietary patterns on risk of preeclampsia, gestational diabetes, preterm birth, small-for-gestational-age (SGA) birth, and a composite of these outcomes.

METHODS

We used data from 8259 participants in the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (8 US medical centers, 2010‒2013). Usual daily periconceptional intake of 82 food groups was estimated from a food frequency questionnaire. We used k-means clustering with a Euclidean distance metric to identify dietary patterns. We estimated the effect of dietary patterns on each perinatal outcome using targeted maximum likelihood estimation and an ensemble of machine learning algorithms, adjusting for confounders including health behaviors and psychological, neighborhood, and sociodemographic factors.

RESULTS

The 4 dietary patterns that emerged from our data were identified as "Sandwiches and snacks" (34% of the sample); "High fat, sugar, and sodium" (29%); "Beverages, refined grains, and mixed dishes" (21%); and "High fruits, vegetables, whole grains, and plant proteins" (16%). One-quarter of pregnancies had preeclampsia (8% incidence), gestational diabetes (5%), preterm birth (8%), or SGA birth (8%). Compared with the "High fat, sugar, and sodium" pattern, there were 3.3 to 4.3 fewer cases of the composite adverse outcome per 100 pregnancies among participants following the "Beverages, refined grains and mixed dishes" pattern (risk difference -0.043; 95% confidence interval -0.078, -0.009), "High fruits, vegetables, whole grains and plant proteins" pattern (-0.041; 95% confidence interval -0.078, -0.004), and "Sandwiches and snacks" pattern (-0.033; 95% confidence interval -0.065, -0.002).

CONCLUSIONS

Our results highlight that there are a variety of periconceptional dietary patterns that are associated with perinatal health and reinforce the negative health implications of diets high in fat, sugars, and sodium.

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 Contribution of Commonly Diagnosed Genetic Disorders to Small for Gestational Age Birth and Subsequent Morbidity and Mortality in Preterm Infants

Objective

Preterm infants born small, vs. appropriate for gestational age (SGA, AGA) are at greater risk for morbidity and mortality. The contribution of genetic disorders to preterm SGA birth, morbidity, and mortality is unknown. We sought to determine the association between genetic disorders and preterm SGA birth, and the association between genetic disorders and morbidity or mortality within preterm SGA infants. We hypothesized that genetic disorders were significantly associated with both.

Study Design

This was a retrospective multicenter cohort study of 409 339 infants, born 23-33 weeks' gestation between 2000 and 2020. The odds of preterm SGA (vs AGA) birth, and the odds of severe morbidity or mortality within SGA preterm infants were determined for infants with genetic disorders, after adjusting for known risk factors.

Results

Genetic disorders were present in 3.0 and 1.3% of SGA and AGA preterm infants respectively; genetic disorders conferred an aOR (95% CI) of 2.06 (1.92, 2.21) of SGA birth. Genetic disorders were present in 4.3 of preterm SGA infants with morbidity or mortality and 2.1% of preterm SGA infants that did not experience morbidity or mortality. Genetic disorders conferred an aOR (95% CI) of 2.12 (2.66, 3.08) of morbidity or mortality.

Conclusions

Genetic disorders are strongly associated with preterm SGA birth, morbidity, and mortality. Clinicians should consider genetic testing of preterm SGA infants, particularly in the setting of other comorbidities or anomalies. Prospective, genomic research is needed to clarify the contribution of genetic disorders to disease in this population.

Is the Biphasic Effect of Diabetes and Obesity on Fetal Growth a Risk Factor for Childhood Obesity?

In pregnancies of women with obesity or diabetes, neonates are often overgrown. Thus, the pregnancy period in these women offers a window of opportunity to reduce childhood obesity by preventing neonatal overgrowth. However, the focus has been almost exclusively on growth in late pregnancy. This perspective article addresses possible growth deviations earlier in pregnancy and their potential contribution to neonatal overgrowth. This narrative review focuses on six large-scale, longitudinal studies that included ∼14,400 pregnant women with at least three measurements of fetal growth. A biphasic pattern in growth deviation, including growth reduction in early pregnancy followed by overgrowth in late pregnancy, was found in fetuses of women with obesity, gestational diabetes mellitus (GDM), or type 1 diabetes compared with lean women and those with normal glucose tolerance. Fetuses of women with these conditions have reduced abdominal circumference (AC) and head circumference (HC) in early pregnancy (observed between 14 and 16 gestational weeks), while later in pregnancy they present the overgrown phenotype with larger AC and HC (from approximately 30 gestational weeks onwards). Fetuses with early-pregnancy growth reduction who end up overgrown presumably have undergone in utero catch-up growth. Similar to postnatal catch-up growth, this may confer a higher risk of obesity in later life. Potential long-term health consequences of early fetal growth reduction followed by in utero catch-up growth need to be explored.

Environmental enteric dysfunction: gut and microbiota adaptation in pregnancy and infancy

Environmental enteric dysfunction (EED) is a subclinical syndrome of intestinal inflammation, malabsorption and barrier disruption that is highly prevalent in low- and middle-income countries in which poverty, food insecurity and frequent exposure to enteric pathogens impair growth, immunity and neurodevelopment in children. In this Review, we discuss advances in our understanding of EED, intestinal adaptation and the gut microbiome over the 'first 1,000 days' of life, spanning pregnancy and early childhood. Data on maternal EED are emerging, and they mirror earlier findings of increased risks for preterm birth and fetal growth restriction in mothers with either active inflammatory bowel disease or coeliac disease. The intense metabolic demands of pregnancy and lactation drive gut adaptation, including dramatic changes in the composition, function and mother-to-child transmission of the gut microbiota. We urgently need to elucidate the mechanisms by which EED undermines these critical processes so that we can improve global strategies to prevent and reverse intergenerational cycles of undernutrition.

An application of group-based trajectory modeling to define fetal growth phenotypes among small-for-gestational-age births in the LIFECODES Fetal Growth Study

BACKGROUND

Reductions in fetal growth are associated with adverse outcomes at birth and later in life. However, identifying fetuses with pathologically small growth remains challenging. Definitions of small-for-gestational age are often used as a proxy to identify those experiencing pathologic growth (ie, fetal growth restriction). However, this approach is subject to limitation as most newborns labeled small-for-gestational age are constitutionally, not pathologically, small. Incorporating repeated ultrasound measures to examine fetal growth trajectories may help distinguish pathologic deviations in growth from normal variability, beyond a simple definition of small-for-gestational age.

OBJECTIVE

This study aimed to characterize phenotypes of growth using ultrasound trajectories of fetal growth among small-for-gestational-age births.

STUDY DESIGN

This study identified and described trajectories of fetal growth among small-for-gestational-age births (<10th percentile weight for gestational age; n=245) in the LIFECODES Fetal Growth Study using univariate and multivariate trajectory modeling approaches. Available ultrasound measures of fetal growth (estimated fetal weight, head circumference, abdominal circumference, and femur length) from health records were abstracted. First, univariate group-based trajectory modeling was used to define trajectories of estimated fetal weight z scores during gestation. Second, group-based multi-trajectory modeling was used to identify trajectories based on concurrent measures of head circumference, abdominal circumference, and femur length z scores. Last, how these trajectories were related to patient demographics, pregnancy characteristics, and birth outcomes compared with those observed among appropriate-for-gestational-age controls was described.

RESULTS

Of note, 3 univariate trajectories of estimated fetal weight and 4 multivariate trajectories of fetal growth among small-for-gestational-age births were identified. In our univariate approach, infants with the smallest estimated fetal weight trajectory throughout pregnancy had poorer outcomes, including the highest risk of neonatal intensive care unit admission. The remaining univariate trajectory groups did not have an elevated risk of adverse birth outcomes relative to appropriate-for-gestational-age controls. In our multivariate approach, 2 groups at increased or moderately increased risk of neonatal intensive care unit admission were identified, including infants that remained extremely small for all parameters throughout pregnancy and those who had disproportionately smaller femur length and abdominal circumference compared with head circumference. The remaining multivariate trajectory groups did not have an elevated risk of adverse birth outcome relative to appropriate-for-gestational-age controls.

CONCLUSION

Latent class group-based trajectory modeling applied to ultrasound measures of fetal growth may help distinguish pathologic vs constitutional growth profiles among newborns born small-for-gestational age. Although trajectories cannot be fully characterized until delivery, limiting the direct clinical application of these methods, they may still contribute to the development of approaches for separating growth restriction from constitutional smallness.

Racial and Ethnic Disparities Among Women Undergoing a Trial of Labor After Cesarean Delivery: Performance of the VBAC Calculator with and without Patients' Race/Ethnicity

The Maternal Fetal Medicine Units Network (MFMU) vaginal birth after cesarean (VBAC) calculator is a clinical tool designed to predict trial of labor after cesarean delivery (TOLAC) success. The calculator has come under scrutiny for its inclusion of race and ethnicity, which systematically predicts a lower likelihood of success for patients who identify as African American or Hispanic. We hypothesized that the calculator would predict VBAC more accurately without the use of race or ethnicity. A retrospective chart review including all patients undergoing TOLAC from 2016 to 2019 was conducted. A multivariate logistic regression was used to compare one model that utilizes the original variables in predicting VBAC (model 1) and another that uses the same variables except for race and ethnicity (model 2). In model 1, race and ethnicity were the only variables not associated with the probability of successful TOLAC (p = 0.065). The area under the curve (AUC) for models 1 and 2 were 0.77 and 0.78, respectively. There was not a statistically significant difference between the predictive abilities of the two models (p = 0.40). Rates of PPH (p = 0.001), abruption (p = 0.04), intra-amniotic infection (p < 0.0001), and other postpartum complications (p = 0.005) differed significantly by race and ethnicity. The use of race and ethnicity did not contribute to the accuracy of VBAC prediction. The use of race and ethnicity in this predictive model should be omitted to prevent inherent bias and discrimination. There were also significant racial and ethnic differences in overall postpartum complication rates.

Sonographic fetal head circumference is associated with trial of labor after cesarean section success

PURPOSE

The purpose is to study the association of the fetal sonographic head circumference (SHC) with trial of labor after cesarean (TOLAC) success rate, among women with no prior vaginal deliveries.

METHODS

A retrospective case-control study including all women with no prior vaginal delivery undergoing TOLAC during 3/2011-6/2020 with a sonographic estimated fetal weight within one week from delivery. TOLAC success and failure groups were compared.

RESULTS

Of 1232 included women, 948 (76.9%) delivered vaginally. The mean fetal SHC was smaller in the TOLAC success group (330 ± 10 vs. 333 ± 11 mm, p < 0.001). In a multivariate regression analysis, predelivery BMI, hypertensive disorders, gestational age at prior CD, SHC and epidural analgesia administration were independently associated with TOLAC success. A ROC analysis of the multivariable model composed of the factors found independently associated with TOLAC success, excluding SHC, yielded an area under curve of 0.659 (95% CI 0.622-0.697) compared with 0.668 (95% CI 0.630-0.705) with SHC included.

CONCLUSION

Smaller SHC is independently associated with TOLAC success among women that did not deliver vaginally before, and has additive clinical value for the prediction of TOLAC success when combined with non-sonographic factors.