Influence of maternal body mass index on interobserver variability of fetal ultrasound biometry and amniotic-fluid assessment in late pregnancy.

OBJECTIVE: To determine the interobserver reproducibility of fetal ultrasound biometric and amniotic-fluid measurements in the third trimester of pregnancy, according to maternal body mass index (BMI) category. METHODS: This was a prospective cohort study of women with a singleton gestation beyond 34 weeks, recruited into four groups according to BMI category: normal (18.0-24.9 kg/m2 ), overweight (25.0-29.9 kg/m2) , obese (30.0-39.9 kg/m2 ) and morbidly obese (≥ 40 kg/m2 ). Multiple pregnancies, women with diabetes and pregnancies with a fetal growth, structural or genetic abnormality were excluded. In each woman, fetal biometric (biparietal diameter (BPD), head circumference, abdominal circumference (AC), femur length (FL) and estimated fetal weight) and amniotic-fluid (amniotic-fluid index (AFI) and maximum vertical pocket (MVP)) measurements were obtained by two experienced sonographers or physicians, blinded to gestational age and each other's measurements. Differences in measurements between observers were expressed as gestational age-specific Z-scores. The interobserver intraclass correlation coefficient (ICC) and Cronbach's reliability coefficient (CRC) were calculated. Bland-Altman analysis was used to assess the degree of reproducibility. RESULTS: In total, 110 women were enrolled prospectively (including 1320 measurements obtained by 17 sonographers or physicians). Twenty (18.2%) women had normal BMI, 30 (27.3%) women were overweight, 30 (27.3%) women were obese and 30 (27.3%) women were morbidly obese. Except for AFI (ICC, 0.65; CRC, 0.78) and MVP (ICC, 0.49; CRC, 0.66), all parameters had a very high level of interobserver reproducibility (ICC, 0.72-0.87; CRC, 0.84-0.93). When assessing reproducibility according to BMI category, BPD measurements had a very high level of reproducibility (ICC ≥ 0.85; CRC > 0.90) in all groups. The reproducibility of AC and FL measurements increased with increasing BMI, while the reproducibility of MVP measurements decreased. Among the biometric parameters, the difference between the BMI categories in measurement-difference Z-score was significant only for FL. Interobserver differences for biometric measurements fell within the 95% limits of agreement. CONCLUSION: Obesity does not seem to impact negatively on the reproducibility of ultrasound measurements of fetal biometric parameters when undertaken by experienced sonographers or physicians who commonly assess overweight, obese and morbidly obese women. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

ISUOG Practice Guidelines: ultrasound assessment of fetal biometry and growth.

INTRODUCTION These Guidelines aim to describe appropriate assessment of fetal biometry and diagnosis of fetal growth disorders. These disorders consist mainly of fetal growth restriction (FGR), also referred to as intrauterine growth restriction (IUGR) and often associated with small­for­gestational age (SGA), and large­for­gestational age (LGA), which may lead to fetal macrosomia; both have been associated with a variety of adverse maternal and perinatal outcomes. Screening for, and adequate management of, fetal growth abnormalities are essential components of antenatal care, and fetal ultrasound plays a key role in assessment of these conditions. The fetal biometric parameters measured most commonly are biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur diaphysis length (FL). These biometric measurements can be used to estimate fetal weight (EFW) using various different formulae1. It is important to differentiate between the concept of fetal size at a given timepoint and fetal growth, the latter being a dynamic process, the assessment of which requires at least two ultrasound scans separated in time. Maternal history and symptoms, amniotic fluid assessment and Doppler velocimetry can provide additional information that may be used to identify fetuses at risk of adverse pregnancy outcome. Accurate estimation of gestational age is a prerequisite for determining whether fetal size is appropriate­for­gestational age (AGA). Except for pregnancies arising from assisted reproductive technology, the date of conception cannot be determined precisely. Clinically, most pregnancies are dated by the last menstrual period, though this may sometimes be uncertain or unreliable. Therefore, dating pregnancies by early ultrasound examination at 8­14 weeks, based on measurement of the fetal crown­rump length (CRL), appears to be the most reliable method to establish gestational age. Once the CRL exceeds 84 mm, HC should be used for pregnancy dating2­4. HC, with or without FL, can be used for estimation of gestational age from the mid­trimester if a first­trimester scan is not available and the menstrual history is unreliable. When the expected delivery date has been established by an accurate early scan, subsequent scans should not be used to recalculate the gestational age1. Serial scans can be used to determine if interval growth has been normal. In these Guidelines, we assume that the gestational age is known and has been determined as described above, the pregnancy is singleton and the fetal anatomy is normal. Details of the grades of recommendation used in these Guidelines are given in Appendix 1. Reporting of levels of evidence is not applicable to these Guidelines.

Pautas de ISUOG para la práctica: evaluación ecográfica de la biometría y el crecimiento fetal INTRODUCCIÓN: El objetivo de estas Pautas es describir la evaluación adecuada de la biometría fetal y el diagnóstico de los trastornos del crecimiento fetal. Estos trastornos consisten principalmente en la restricción del crecimiento fetal (RCF), también conocida como restricción del crecimiento intrauterino (RCIU), que a menudo está asociada con un tamaño pequeño para la edad gestacional (PEG) o grande para la edad gestacional (GEG), que pueden dar lugar a la macrosomía fetal; ambos se han asociado con una variedad de resultados maternos y perinatales adversos. La detección y el tratamiento adecuado de las anomalías del crecimiento fetal son componentes esenciales de la atención prenatal, y la ecografía fetal desempeña un papel fundamental en la evaluación de estas afecciones. Los parámetros biométricos fetales medidos con mayor frecuencia son (todas las siglas procedentes del inglés) el diámetro biparietal (BPD), el perímetro cefálico (HC), el perímetro abdominal (AC) y la longitud de la diáfisis del fémur (FL). Estas mediciones biométricas se pueden utilizar para estimar el peso del feto (PEF) mediante fórmulas diferentes1 . Es importante diferenciar entre el concepto de tamaño fetal en un momento dado y el crecimiento fetal en sí, siendo este último un proceso dinámico cuya evaluación requiere al menos dos ecografías separadas en el tiempo. La historia y los síntomas de la madre, la evaluación del líquido amniótico y la velocimetría Doppler pueden proporcionar información adicional que se puede utilizar para identificar los fetos bajo riesgo de resultados adversos del embarazo. La estimación precisa de la edad gestacional es un prerrequisito para determinar si el tamaño del feto es apropiado para la edad gestacional (AEG). Excepto en el caso de los embarazos procedentes de tecnologías de reproducción asistida, la fecha de concepción no se puede determinar con precisión. Clínicamente, la fecha de la mayoría de los embarazos se establece en función del último período menstrual, aunque a veces esto puede ser incierto o poco fiable. Por lo tanto, el fechado de los embarazos mediante ecografía temprana a las 8-14 semanas, mediante la medición de la longitud céfalo-caudal (LCC) fetal, parece ser el método más fiable para establecer la edad gestacional. Una vez que la LCC excede los 84 mm, se debe usar el HC2-4 para establecer la fecha del embarazo. El HC, con o sin FL, se puede utilizar para estimar la edad gestacional a partir de la mitad del primer trimestre si no se dispone de una ecografía del primer trimestre y el historial menstrual no es fiable. Cuando se ha establecido la fecha prevista del parto mediante una exploración temprana precisa, no se deben utilizar exploraciones posteriores para recalcular la edad gestacional1 . Las exploraciones en serie se pueden utilizar para determinar si el intervalo del crecimiento ha sido normal. En estas Pautas se asume que la edad gestacional es conocida y ha sido determinada según lo anterior, que el embarazo es de feto único y que la anatomía fetal es normal. En el Apéndice 1 se detallan los grados de recomendación utilizados en estas Pautas. El informe sobre los niveles de evidencia no es aplicable a estas Pautas.

A rapid questionnaire assessment of environmental exposures to pregnant women in the INTERGROWTH-21st Project.

Impaired fetal growth and preterm birth are the leading causes of neonatal and infant mortality worldwide and there is a growing scientific literature suggesting that environmental exposures during pregnancy may play a causal role in these outcomes. Our purpose was to assess the environmental exposure of the Fetal Growth Longitudinal Study (FGLS) participants in the multinational INTERGROWTH-21(st) Project. First, we developed a tool that could be used internationally to screen pregnant women for such exposures and administered it in eight countries on a subsample (n = 987) of the FGLS participants. The FGLS is a study of fetal growth among healthy pregnant women living in relatively affluent areas, at low risk of adverse pregnancy outcomes and environmental exposures. We confirmed that most women were not exposed to major environmental hazards that could affect pregnancy outcomes according to the protocol's entry criteria. However, the instrument was able to identify some women that reported various environmental concerns in their homes such as peeling paint, high residential density (>1 person per room), presence of rodents or cockroaches (hence the use of pesticides), noise pollution and safety concerns. This screening tool was therefore useful for the purposes of the project and can be used to ascertain environmental exposures in studies in which the primary aim is not focused on environmental exposures. The instrument can be used to identify subpopulations for more in-depth assessment, (e.g. environmental and biological laboratory markers) to pinpoint areas requiring education, intervention or policy change.

Second-trimester assessment of gestational age in twins: validation of singleton biometry charts.

OBJECTIVE: To determine the accuracy of dating twin pregnancies, of between 16 and 26 weeks' gestation, using singleton head circumference (HC) formulae. METHODS: This was a retrospective study of 269 singleton and 119 twin non-anomalous pregnancies conceived by in-vitro fertilization (IVF) with a known embryo transfer date. Fetal ultrasound biometry data for HC, obtained using different formulae, were compared with expected fetal HC size for gestation calculated from the date of conception. Similar comparisons were undertaken for femur length (FL) and for transverse cerebellar diameter. RESULTS: The mean differences in HC between observed ultrasound measurements and those expected from the IVF history were small (1-4 mm) and within the measurement error for both singletons and twins for all formulae. All measurements from the larger and the smaller twins straddled those of singletons, regardless of biometry and formula used. Negative skewing of FL measurements in the smaller twin suggests that fetal growth restriction may occur at this gestation and supports the practice of dating using the HC of the larger twin. CONCLUSIONS: Singleton pregnancy HC charts can be used to date reliably twin pregnancies. The data of the study also suggest that the HC of the larger twin is the most reliable measurement for use in dating.

Obstetric ultrasound scanning by local health workers in a refugee camp on the Thai-Burmese border.

OBJECTIVES: Ultrasound examination of the fetus is a powerful tool for assessing gestational age and detecting obstetric problems but is rarely available in developing countries. The aim of this study was to assess the intraobserver and interobserver agreement of fetal biometry by locally trained health workers in a refugee camp on the Thai-Burmese border. METHODS: One expatriate doctor and four local health workers participated in the study, which included examinations performed on every fifth pregnant woman with a singleton pregnancy between 16 and 40 weeks' gestation, and who had undergone an early dating ultrasound scan, attending the antenatal clinic in Maela refugee camp. At each examination, two examiners independently measured biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL), with one of the examiners obtaining duplicate measurements of each parameter. Intraobserver measurement error was assessed using the intraclass correlation coefficient (ICC) and interobserver error was assessed by the Bland and Altman 95% limits of agreement method. RESULTS: A total of 4188 ultrasound measurements (12 per woman) were obtained in 349 pregnancies at a median gestational age of 27 (range, 16-40) weeks in 2008. The ICC for BPD, HC, AC and FL was greater than 0.99 for all four trainees and the doctor (range, 0.996-0.998). For gestational ages between 18 and 24 weeks, interobserver 95% limits of agreement corresponding to differences in estimated gestational age of less than +/- 1 week were calculated for BPD, HC, AC and FL. Measurements by local health workers showed high levels of agreement with those of the expatriate doctor. CONCLUSIONS: Locally trained health workers working in a well organized unit with ongoing quality control can obtain accurate fetal biometry measurements for gestational age estimation. This experience suggests that training of local health workers in developing countries is possible and could allow effective use of obstetric ultrasound imaging.

Functional linear discriminant analysis: a new longitudinal approach to the assessment of embryonic growth.

BACKGROUND: Functional linear discriminant analysis (FLDA) is a new growth assessment technique using serial measurements to discriminate between normal and abnormal fetal growth. We used FLDA to assess and compare growth in live pregnancies destined to miscarry with those remaining viable. METHODS: This was a prospective cohort study of women with ultrasound scans on at least two separate occasions showing live pregnancies. Serial crown-rump length (CRL), mean gestational sac diameter and mean yolk sac diameter measurements were recorded. The ability of FLDA to predict subsequent miscarriage was compared with that of a single CRL measurement. RESULTS: Of 521 included pregnancies, 493 (94.6%) remained viable at 14 weeks and 28 (5.4%) miscarried. The CRL growth rate was significantly lower in those that miscarried (one-sample t-test, P = 2.638E-22). The sensitivity of FLDA in predicting miscarriage from serial CRL measurements was 60.7% and specificity was 93.1% [positive predictive value (PPV) 33.3%, negative predictive value (NPV) 97.7%]. This was significantly better for predicting miscarriage than a single CRL observation of more than 2SD below that expected (sensitivity 53.6%, specificity 72.2%, PPV 9.9%, NPV 96.5%). CONCLUSIONS: FLDA discriminates between normal and abnormal growth to predict miscarriage with high specificity. FLDA predicts miscarriage better than a single observation of a small CRL.