Fetal sacral length in the ultrasonographic assessment of gestational age

Second and third trimester estimation of gestational age using ultrasound or maternal symphysis-fundal height measurements: A systematic review

Many vulnerable women seek antenatal care late in pregnancy. How should gestational age be determined? We examine all available studies estimating GA >20 weeks. Ultrasound is much better than fundal height, and using cerebellar measurement appears to be the most accurate.

Linked article: This article is commented on by Philip J. Steer, pp. 1459 in this issue. To view this minicommentary visit https://doi.org/10.1111/1471‐0528.17127 .

Sonographic Assessment of Fetal Growth Abnormalities

Fetal growth abnormalities have significant consequences for pregnancy management and maternal and fetal well-being. The accurate diagnosis of fetal growth abnormalities contributes to optimal antenatal management, which may minimize the sequelae of inadequate or excessive fetal growth. An accurate diagnosis of abnormal fetal growth depends on accurate pregnancy dating and serial growth measurements. The fetal size at any given stage of pregnancy is either appropriate or inappropriate for the given gestational age (GA). Pregnancy dating is most accurate in the first trimester, as biologic variability does not come into play until the second and third trimesters. The authors describe the determination of GA with use of standard US measurements and how additional parameters can be used to confirm dating. Once dates are established, serial measurements are used to identity abnormal growth patterns. The sometimes confusing definitions of abnormal growth are clarified, the differentiation of a constitutionally small but healthy fetus from a growth-restricted at-risk fetus is described, and the roles of Doppler US and other adjunctive examinations in the management of growth restriction are discussed. In addition, the definition of selective growth restriction in twin pregnancy is briefly discussed, as is the role of Doppler US in the classification of subtypes of selective growth restriction in monochorionic twinning. The criteria for diagnosing macrosomia and the management of affected pregnancies also are reviewed. The importance of correct pregnancy dating in the detection and surveillance of abnormal fetal growth and for prevention of perinatal maternal and fetal morbidity and mortality cannot be overstated. The online slide presentation from the RSNA Annual Meeting is available for this article. ^©RSNA, 2020.

Guideline No. 388-Determination of Gestational Age by Ultrasound

OBJECTIVE

To assist clinicians in assigning gestational age based on ultrasound biometry.

OUTCOMES

To determine whether ultrasound dating provides more accurate gestational age assessment than menstrual dating with or without the use of ultrasound. To provide maternity health care providers and researchers with evidence-based guidelines for the assignment of gestational age. To determine which ultrasound biometric parameters are superior when gestational age is uncertain. To determine whether ultrasound gestational age assessment is cost effective.

EVIDENCE

Published literature was retrieved through searches of PubMed or MEDLINE and The Cochrane Library in 2013 using appropriate controlled vocabulary and key words (gestational age, ultrasound biometry, ultrasound dating). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies written in English. There were no date restrictions. Searches were updated on a regular basis and incorporated in the guideline to July 31, 2013. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.

VALUES

The quality of evidence in this document was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care (Table 1).

BENEFITS, HARMS, AND COSTS

Accurate assignment of gestational age may reduce post-dates labour induction and may improve obstetric care through allowing the optimal timing of necessary interventions and the avoidance of unnecessary ones. More accurate dating allows for optimal performance of prenatal screening tests for aneuploidy. A national algorithm for the assignment of gestational age may reduce practice variations across Canada for clinicians and researchers. Potential harms include the possible reassignment of dates when significant fetal pathology (such as fetal growth restriction or macrosomia) result in a discrepancy between ultrasound biometric and clinical gestational age. Such reassignment may lead to the omission of appropriate-or the performance of inappropriate-fetal interventions.

SUMMARY STATEMENTS

RECOMMENDATIONS.

Normal development of sacrococcygeal centrum ossification centers in the fetal spine: a postmortem magnetic resonance imaging study

PURPOSE

To describe the temporal pattern of the appearance of the S1-Co1 centrum ossification centers (COCs) and provide reference data for the S1-S5 COCs and sacral length at various gestational ages (GAs).

METHODS

Postmortem magnetic resonance imaging (MRI) was performed on 71 fetuses (GA, 17-42 weeks) using the 3D dual-echo steady-state with water excitation T2 sequence in the sagittal plane. To confirm the reliability of this sequence, the MRI data were compared with the CT and histologic data obtained from two fetuses (GAs, 21 and 30 weeks). The presence or absence of each sacrococcygeal COC was recorded. Sacral length and S1-S5 COC height, sagittal diameter, transverse diameter, cross-sectional area, and volume were measured.

RESULTS

All fetuses showed S1-S3 COCs by 17 weeks, S4 COCs by 19 weeks, and S5 COCs by 28 weeks. The S4, S5, and Co-1 COCs were visualized in 70 (98.59%), 51 (71.83%), and 21 (29.58%) fetuses, respectively. Sacral length, height, sagittal, and transverse diameters increased linearly, while cross-sectional area and volume increased exponentially with advancing GA. Mean growth rates of the sagittal and transverse diameters, cross-sectional area, and volume, but not of height, significantly differed among the S1-S5 vertebrae.

CONCLUSION

We have presented the timing of appearance of individual sacrococcygeal COCs and the age-specific, normative MRI reference values for sacral length and the morphometric parameters of the sacral COCs, which are of clinical importance in the diagnosis of congenital sacral abnormalities and skeletal dysplasia.

Détermination de l'âge gestationnel par échographie

OBJECTIF

Aider les cliniciens à attribuer un âge gestationnel en fonction des résultats de la biométrie échographique.

ISSUES

Déterminer si la datation par échographie offre une évaluation plus précise de l'âge gestationnel que la datation en fonction des dernières règles avec ou sans recours à l'échographie. Offrir, aux praticiens et aux chercheurs du domaine des soins de maternité, des lignes directrices factuelles en matière d'attribution de l'âge gestationnel. Identifier les paramètres biométriques échographiques qui sont de fiabilité supérieure lorsque l'âge gestationnel est incertain. Déterminer la rentabilité de l'évaluation de l'âge gestationnel par échographie. RéSULTATS: La littérature publiée a été récupérée par l'intermédiaire de recherches menées dans PubMed ou MEDLINE et The Cochrane Library en 2013 au moyen d'un vocabulaire contrôlé et de mots clés appropriés (p. ex. « gestational age », « ultrasound biometry » et « ultrasound dating »). Les résultats ont été restreints aux analyses systématiques, aux essais comparatifs randomisés / essais cliniques comparatifs et aux études observationnelles rédigés en anglais. Aucune restriction n'a été appliquée en matière de dates. Les recherches ont été mises à jour de façon régulière et intégrées à la directive clinique jusqu'au 31 juillet 2013. La littérature grise (non publiée) a été identifiée par l'intermédiaire de recherches menées dans les sites Web d'organismes s'intéressant à l'évaluation des technologies dans le domaine de la santé et d'organismes connexes, dans des collections de directives cliniques, dans des registres d'essais cliniques et auprès de sociétés de spécialité médicale nationales et internationales.

VALEURS

La qualité des résultats est évaluée au moyen des critères décrits dans le rapport du Groupe d'étude canadien sur les soins de santé préventifs (Tableau 1). AVANTAGES, DéSAVANTAGES ET COûTS: L'attribution précise d'un âge gestationnel pourrait réduire l'incidence du déclenchement mené en raison d'une grossesse prolongée et améliorer les soins obstétricaux en nous permettant de planifier la chronologie des interventions nécessaires de façon optimale et d'éviter les interventions inutiles. Une datation plus précise permet l'optimisation de la tenue de tests prénataux de dépistage de l'aneuploïdie. Un algorithme national d'attribution de l'âge gestationnel pourrait atténuer les variations pancanadiennes en matière de pratique pour les cliniciens et les chercheurs. Parmi les désavantages potentiels, on trouve la réattribution possible des dates lorsqu'une pathologie fœtale importante (comme le retard de croissance intra-utérin ou la macrosomie) donne lieu à une divergence entre les résultats de la biométrie échographique et l'âge gestationnel clinique. Une telle réattribution pourrait mener à l'omission d'interventions fœtales justifiées ou à la tenue d'interventions fœtales injustifiées. DéCLARATIONS SOMMAIRES: RECOMMANDATIONS.

Normal Fetal Growth Assessment: A Review of Literature and Current Practice

A review of literature and current practice of normal fetal growth assessment is presented. Ultrasonographic dating of pregnancy in the first, second, and third trimester is reviewed. Individual biometric parameters are examined, and the proper use of the fetal growth profile is explained. Use of this information is discussed as it pertains to the single pregnancy.

2D Sonographic Assessment of the Fetal Liver in Normal Pregnant Nigerian Women

This study investigated the relationship between fetal liver volume (FLV) and gestational age (GA) in Nigerian subjects using 2D sonography. Fetal liver volume measurements were obtained from 900 normal singleton fetuses between 15 and 41 weeks GA (mean = 28 weeks). The FLV was computed from anterior-posterior, sagittal, and transverse dimensions of the fetal liver by assuming the liver to be a pyramidal structure. The mean FLV obtained ranged from 4.14 ± 0 cm 3 at 15 weeks to 76.88 ± 7.58 cm3 at 40 weeks and 79.45 ± 9.32 cm3 at 41 weeks. A simple regression analysis showed a positive linear relationship between GA and FLV ( r = 0.98), which is described by the equation FLV = 53.53 + 3.246 GA. A strong positive correlation was also noted between FLV and biparietal diameter (BPD; r = 0.968), FLV and head circumference ( r = 0.960), FLV and abdominal circumference ( r = 0.901), and FLV and fetal weight ( r = 0.979). Z test analysis showed no significant difference between GA estimated by FLV and GA estimated by BPD or femur length (α = 0.01). The use of FLV determined by 2D sonography has been shown to be accurate in dating pregnancy, and its use in a multiparameter biometry should improve the precision in predicting the expected date of delivery.

Fetal spine ossification: the gender and individual differences illustrated by ultrasonography

The spatial and temporal pattern of manifestation of ossification nuclei of the spinal column in fetal life have been well established by histologic and radiologic studies. Sonographic evaluation of the fetal spine depends on visualization of the ossification centers, but the sequence of development of ossification centers in the vertebral column obtained by embryologists and sonographers and radiology are conflicting. We carried out a longitudinal study to establish the ultrasonographic appearance and timing of development of primary ossification centers of the fetal spine in the first and second trimesters of pregnancy. A total of 80 mothers were evaluated during their pregnancy with two echographic controls; in the first trimester, the spine length was measured and, in the second trimester of pregnancy, the timing of ossification of the bodies and neural arches of sacral vertebrae and the difference in appearance between the female and male genders were evaluated. Spinal length measurements obtained in the first trimester and percentage of detection of sacral vertebral structures increased progressively with a regular pattern in relation to gestational age. Spinal length at first ultrasound examination was slightly correlated with time of appearance of sacral bodies and arches. Ossification timing was significantly earlier in females than in males. The study has attempted to improve our understanding of the sonographic detection of the spinal ossification. Data presented give some further information on the stages of appearance of sacral vertebrae body centers during intrauterine development. Differences between genders and interindividual variations in ossification timing were observed at a very early stage of development. This could be of value when fetal growth is evaluated. Moreover, further knowledge of spinal development may be useful for early diagnosis of spinal abnormalities and for fetal biometrics.

Estimation of gestational maturity of preterm infants by five fetal sonographic measurements compared with neonatal EEG and the last menstrual period

We previously reported no differences in estimates of gestational maturity between a cumulative score based on sonographic/obstetrical measurements and an EEG interpretation for healthy preterm neonates. For the present study, a rank order among 5 fetal sonographic measurements was used to estimate gestational age: head circumference, transcerebellar diameter, biparietal diameter, femur length, and abdominal circumference were compared with an electroencephalographic estimate and an arithmetic estimate of maturity (i.e., the mother's last menstrual period). A fetal sonographic study for each of 13 premature neonates (i.e., born at < 32 weeks estimated gestational age) was followed after birth by a neonatal EEG recording. EEG and sonographic estimates of maturity were assigned without knowledge of other clinical data. The mother's last menstrual period was obtained from the medical record. Principal component analysis determined that 86% of the variance was evenly distributed over the 5 sonographic measurements. Using a regression procedure, 61% of the variance (adjusted r2 = 0.61) was explained by EEG when compared with fetal sonographic estimates. Only 19% (adjusted r2 = 0.19) of the variance was explained by the estimate based on the mother's last menstrual period. Optimal subset selection determined that the rank order for prediction of gestational maturity among the fetal sonographic measurements was as follows: (1) head circumference; (2) transcerebellar diameter; (3) biparietal diameter; (4) femur length; (5) abdominal circumference. Cranial measurements on fetal sonography (i.e., head circumference, transcerebellar diameter, biparietal diameter) compared more closely with EEG estimates than non-cranial measurements (i.e., femur length and abdominal circumference). In conclusion, neonatal EEG estimates of gestational maturity compared more closely with sonographic measurements than estimates based on the time of the last menstrual period. These findings will be useful in situations when dates of conception are unknown or inaccurate, or when intrauterine growth restriction causes discrepancies in growth rates between cranial and non-cranial fetal measurements on sonography.

Comparative estimates of neonatal gestational maturity by electrographic and fetal ultrasonographic criteria

We previously reported a high correlation between electrographic and postmortem neuroanatomic (i.e., sulcal-gyral) estimates of maturity in sick preterm neonates who were clinically abnormal because of neonatal medical illnesses. Electroencephalographic studies have not yet been compared with ultrasonographic measurements in healthy fetuses who subsequently had normal neurodevelopmental outcome. Twenty-five EEG recordings on healthy neonates (28-43 weeks postconceptional age) had EEG estimates of gestational maturity without knowledge of obstetric, neonatal, or ultrasonographic criteria. Thirteen recordings from this cohort were obtained on very premature neonates (i.e., < 32 weeks estimated gestational age). Fetal ultrasonographic determinations of gestational maturity for these 13 subjects were also obtained prior to birth. Ultrasonographic estimates were assigned without knowledge of other clinical data. Gestational age estimates based on electroencephalographic analyses were compared with 5 ultrasonographic estimates of gestational age maturity using multivariate regression (i.e., biparietal diameter, abdominal circumference, femur length, transcerebellar diameter, and head circumference), as well as the mother's last menstrual period. No significant differences were detected between the electrographic and obstetric/ultrasonographic estimates of gestational maturity. An electroencephalographer's assessment of gestational age is as accurate as the fetal ultrasonographic estimates in the asymptomatic preterm neonate whose gestational age is < 32 weeks at birth.