Two- and three-dimensional sonographic diagnosis of fetal intra-abdominal umbilical vein varix: A case report

Fetal intra‐abdominal umbilical vein varix is a rare condition characterized by focal dilatation of the umbilical vein of the fetus. We report a case of fetal intra‐abdominal umbilical vein varix associated with additional sonographic abnormalities and detected at 31 weeks' gestation. Several follow‐up sonographic examinations were performed, and the prenatal findings were confirmed on postnatal ultrasound. The diagnosis was facilitated by the use of three‐dimensional power Doppler sonography. © 2012 Wiley Periodicals, Inc. J Clin Ultrasound, 2012;     

Three‐Dimensional Ultrasonography of the Fetal Vermis at 18 to 26 Weeks' Gestation

Objective. The purpose of this study was to establish the normality of the fetal vermis, ie, the time of appearance of the primary fissure, as well as its measurements between 18 and 26 weeks' gestation, using 3‐dimensional (3D) ultrasonography. Methods. A prospective cross‐sectional study of normal singleton pregnancies was conducted. Examinations were performed with high‐resolution transabdominal ultrasonography using the axial plane in 173 fetuses between 18 and 26 weeks' gestation. Postprocessing measurements of the fetal vermis were done with 4‐dimensional software using static volume contrast imaging and tomographic ultrasound imaging in the C‐plane. Detection of the primary fissure was evaluated in all cases, and the time of appearance was documented. Results. Adequate vermis measurements were obtained in 173 fetuses. Vermian length as a function of gestational age was expressed by regression equations, and the correlation coefficients were found to be highly statistically significant (P < .001). The normal mean ± 2 SD for each gestational week was defined. The primary fissure was observed at 24 weeks' gestation in all cases, at 22 weeks in 94% of cases, and as early as 18 weeks in 40%. Conclusions. This 3D study documents the appearance of the primary fissure and presents the normal range of vermian measurements, confirming normal development of the fetal vermis starting as early as 18 weeks' gestation. It also shows an easy method for visualizing the vermis with 3D ultrasonography at every gestational week regardless of fetal presentation.     

Interobserver Reproducibility of Transabdominal 3‐Dimensional Sonography of the Fetal Brain

Objective. The purpose of this study was to assess the interobserver reproducibility of transabdominal 3‐dimensional (3D) fetal neurosonography. Methods. This was a prospective observational study. We studied 23 consecutive singleton pregnancies between 18 and 23 weeks' gestation. All cases had normal fetal neurosonographic examination findings, which were confirmed after birth. A 3D sonographic volume of the fetal head was acquired transabdominally by a single operator using an axial approach. Fetal brain anatomy was later analyzed offline by 2 different operators. Axial, sagittal, and coronal views of the fetal brain were obtained to perform a detailed evaluation of the fetal brain. Each operator defined the scanning planes obtained as adequate or inadequate. Results were evaluated with 2 × 2 tables and the Cohen κ coefficient to assess interobserver agreement. Results. Good‐quality multiplanar images were obtained in 23 of 23 cases. The rate of adequate visualization was 100% for all of the axial planes, with κ values of 1.00. For sagittal and coronal planes, the rate of visualization ranged between 78% and 91%, with κ values ranging between 0.61 and 0.83. Conclusions. Transabdominal 3D sonography of the fetal brain at 18 to 23 weeks' gestation has an acceptable degree of interobserver reproducibility.     

Prenatal sonographic diagnosis of short umbilical cord in a dichorionic twin with normal fetal anatomy

Short umbilical cords are associated with fetal anomalies, often including those with decreased or absent fetal movement, fetal akinesia/hypokinesia sequence, and restrictive dermopathies and aneuploidy. In normal fetuses, abnormally short umbilical cords have been associated with an increased risk of umbilical vessel hematomas, thrombosis, rupture, thrombocytopenia, cord compression, variable fetal heart rate decelerations, instrumental and operative deliveries, and fetal demise. We report a 24‐year‐old gravida 2, para 0 with a concordant dichorionic twin gestation, at 26 weeks' gestation, in whom sonography depicted fetuses with normal‐appearing anatomy as well as short umbilical cord of the 1st twin. Increased fetal surveillance was conducted. Following delivery at 36 weeks' gestation, the presence of a short umbilical cord of the 1st twin measuring 19 cm was confirmed. Systematic review of the literature confirms that this is the first report of prenatal diagnosis of a short umbilical cord in an otherwise normal fetus. © 2009 Wiley Periodicals, Inc. J Clin Ultrasound 2010     

Patterns of Fetal Growth in a Rural Indian Cohort and Comparison With a Western European Population

Objective. The purpose of this study was to describe fetal size on sonography in a rural Indian population and compare it with those in European and urban Indian populations. Methods . Participants were from the Pune Maternal Nutrition Study of India. Fetal growth curves were constructed from serial ultrasound scans at approximately 18, 30, and 36 weeks' gestation in 653 singleton pregnancies. Measurements included femur length (FL), abdominal circumference (AC), biparietal diameter (BPD), and occipitofrontal diameter, from which head circumference (HC) was estimated. Measurements were compared with data from a large population‐based study in France and a study of urban mothers in Vellore, south India. Results. Fetal AC and BPD were smaller than the French reference at 18 weeks' gestation (?1.38 and ?1.30 SD, respectively), whereas FL and HC were more comparable (?0.77 and ?0.59 SD). The deficit remained similar at 36 weeks for AC (?0.97 SD), FL (?0.43 SD), and HC (?0.52 SD) and increased for BPD (?2.3 SD). Sonography at 18 weeks underestimated gestational age compared with the last menstrual period date by a median of ?1.4 (interquartile range, ?4.6, 1.8) days. The Pune fetuses were smaller, even at the first scan, than the urban Vellore sample. Conclusions. Fetal size was smaller in a rural Indian population than in European and urban Indian populations, even in mid pregnancy. The deficit varied for different fetal measurements; it was greatest for AC and BPD and least for FL and HC.     

Fetal Megacystis

The purpose of our retrospective observational series was to determine whether the sonographic characteristics of fetal megacystic bladders can be used to reliably establish the most likely diagnosis in fetuses with this condition. The sonographic records of pregnant patients referred to our institutions over a 10‐year period who were found on initial 2‐dimensional sonography to be carrying fetuses with megacystis were examined for evidence of a keyhole sign, bladder thickness, amniotic fluid index, and fetal sex. When available, 3‐/4‐dimensional sonography, Doppler angiography, tomographic ultrasound imaging, virtual organ computer‐aided analysis, and automatic volume calculation were used as part of the detailed fetal anatomic survey. Twenty fetuses with megacystis were identified. Seventeen were male; 2 were female; and 1 had ambiguous genitalia. All male fetuses with megacystis originally had a diagnosis of prune belly syndrome. The diagnosis for 10 male fetuses with a keyhole sign was changed to megacystis secondary to posterior urethral valves. The fetus with ambiguous genitalia had prune belly syndrome. One of the female fetuses had a diagnosis of urethral atresia, and the diagnosis for the other female fetus was megacystis‐microcolon‐intestinal hypoperistalsis syndrome. In conclusion, in fetuses with megacystic bladders, it is possible to distinguish between cases with prune belly syndrome, posterior urethral valves, urethral atresia, and megacystis‐microcolon‐intestinal hypoperistalsis syndrome by a detailed anatomic survey using 2‐ and 3‐/4‐dimensioinal sonographic techniques.     

Evaluation of the Fetal Secondary Palate by 3‐Dimensional Ultrasonography

Objective. Diagnosis of cleft lip and palate remains a challenge with 2‐dimensional ultrasonography, particularly when clefting involves only the secondary palate. The utility of 3‐dimensional ultrasonography (3DUS) has enhanced our ability to detect clefts. We report our experience with a modification of the flipped face technique to aid in the diagnosis of clefting of the secondary palate. Methods. Ninety‐two volumes of 92 fetal faces were evaluated. Thirty‐six volumes were acquired prospectively. Fifty‐six volumes had previously been acquired and included 8 with clefting of the secondary palate. Volumes were obtained on 3DUS systems and reviewed by 4 blinded readers on personal computer workstations. Volumes were manipulated so that an upright profile was visualized. The palate was then rendered using a thin, curved render box. Statistical analysis was performed using the Fisher exact test for categorical data. Intraclass correlations were computed to assess inter‐rater agreement. Results. The mean gestational age at image acquisition ± SD was 22 ± 5 weeks. Image quality of the secondary palate was obtained and rated as adequate by at least 2 reviewers in 34% (31 of 92) of volumes. The sensitivity of cleft detection ranged from 33% to 63%, and the specificity ranged from 84% to 95%. The low sensitivity was mainly due to artifacts/shadowing. The inter‐rater reliability was 0.62 (95% confidence interval, 0.47–0.76). Conclusions. Three‐dimensional ultrasonography can be used to diagnose clefts of the secondary palate. This evaluation is limited by the fetal position and artifacts from shadowing of adjoining structures. Pseudoclefts can be created, and optimal imaging cannot be obtained in all fetuses.     

Frontomaxillary Facial Angle Measurements in Euploid Korean Fetuses at 11 Weeks' to 13 Weeks 6 Days' Gestation

Objective. The purpose of this study was to evaluate the distribution of fetal frontomaxillary facial angles in a euploid Korean population at 11 weeks' to 13 weeks 6 days' gestation. Methods. Three‐dimensional volumes of the fetal head were obtained from women with low‐risk singleton pregnancies at 11 weeks' to 13 weeks 6 days' gestation who consented to this prospective study. Only fetuses with either a normal karyotype confirmed by amniocentesis or no abnormalities after delivery were considered eligible for analysis and were characterized as euploid for the purposes of this study. Women with multiple pregnancies and those who were lost to follow‐up and fetuses with abnormal karyotypes or anomalies diagnosed in utero or postnatally were excluded. The frontomaxillary facial angle was measured twice offline by a single examiner. Cases were categorized by crown‐rump length (CRL) in 10‐mm intervals for analysis of the frontomaxillary facial angle. Results. Among 375 enrolled cases, 158 were eligible for frontomaxillary facial angle analysis. The overall mean frontomaxillary facial angle ± SD was 88.6° ± 9.7°. The mean frontomaxillary facial angle for fetuses with a CRL of 40 to 49 mm (n = 35) was 93.7°; 50 to 59 mm (n = 53), 92.6°; 60 to 69 mm (n = 36), 85.3°; and 70 to 79 mm (n = 34), 81.0°, showing an inverse relationship between the mean frontomaxillary facial angle and CRL (r = ?0.5334; P < .0001). The proportion of cases with frontomaxillary facial angles of 85° or greater was 60.8%, and that of cases with angles of 90° or greater was 37.3%. Conclusions. Ethnic differences in frontomaxillary facial angle measurements should be considered when incorporating the frontomaxillary facial angle in fetal aneuploidy screening in the Korean population.     

Development of the Fetal Spinal Cord

Objective. The purpose of this study was to perform high‐resolution sonographic examinations to determine the normal anatomic relationship of the conus medullaris (CM) of the spinal cord with the vertebral column during different stages of gestation. Methods. In this prospective study, fetal sonographic evaluations were performed between 13 and 40 weeks' gestation. Transvaginal probes (7.5–8 MHz) or abdominal probes (5–8 MHz) were used, depending on gestational age and position of the fetus. The CM was located in coronal longitudinal sections. The positions of the kidneys and lumbosacral junction and the origin of the ribs determined the location of the vertebrae. The locations of the CM were divided into 5 groups according to their positions relative to the vertebrae. Results. A total of 110 fetuses between 13 and 40 weeks' gestation were studied. Between 13 and 18 weeks' gestation, the CM was situated at the level of the L4 vertebra, or more caudally, in 100% of the fetuses. At term, all fetuses showed the CM above L2. A distinct ascent of the CM was detected between 13 and 40 weeks' gestation. The results were statistically significant (P <.0001). Conclusions. A distinguishable ascent of the CM in relation to the vertebral column during fetal life was detected.     

Three‐Dimensional Ultrasonographic Depiction of Fetal Abdominal Blood Vessels

Objective. The purpose of this study was to identify fetal abdominal vasculature with 3‐dimensional (3D) ultrasonography and to describe a systematic method for analysis of volume data sets. Methods. Three‐dimensional volumes of the fetal abdomen were acquired prospectively in 30 patients between 15 and 34 weeks' gestation with color Doppler, high‐definition (HD) flow, power Doppler, and B‐flow imaging. All volumes were analyzed offline by 2 examiners separately. The feasibility of identifying the fetal abdominal blood vessels was analyzed. A standardized approach was applied to identify specific vessels by correlating the images with known anatomic landmarks. Results. The volumes were rotated into an anatomic orientation in the multiplanar mode, and then the vessels were identified in the following order: aorta (30 of 30), celiac trunk (29 of 30), superior mesenteric vein (28 of 30 and 26 of 30 for readers 1 and 2, respectively), superior mesenteric artery (29 of 30), left renal artery (25 of 30 and 26 of 30), right renal artery (27 of 30), common iliac arteries (30 of 30), umbilical arteries (26 of 27), external iliac arteries (20 of 22), umbilical vein (29 of 30), ductus venosus (30 of 30), hepatic vein (29 of 30), right portal vein (29 of 30), inferior vena cava (28 of 30), adrenal artery (2 of 30), hepatic artery (24 of 30 and 23 of 30), splenic artery (24 of 30 and 23 of 30), gastric artery (14 of 30 and 9 of 30), splenic vein (19 of 30 and 15 of 30), and renal vein (1 of 30). A step‐by‐step systematic approach to identify the abdominal vasculature from the ultrasonographic volume data set was developed. Conclusions. Fetal abdominal vessels can be easily visualized when a systematic analysis is performed on 3D data set volumes. Visualization of the vessels was optimal when volumes were acquired with HD flow imaging.     

Sonographic Measurements of the Thymus in Male and Female Fetuses

Objective. The purpose of this study was to determine whether the size of the thymus is different in male and female fetuses. Methods. In this prospective study, the transverse diameter and perimeter of the thymus were measured in healthy fetuses between 24 and 37 weeks' gestation. The means of the study variables from male and female fetuses were compared by the Student t test, and the relationships between the transverse diameter and perimeter of the thymus and gestational age and other common fetal biometric parameters were determined by linear regression modeling. Results. No differences were noted between male and female fetuses for the means of the study variables. After the relationship between the transverse diameter and perimeter of the thymus and gestational age was confirmed (R² = 0.8 and 0.75, respectively; both P < .01), the 95% confidence interval–predicted changes were calculated, and the scatterplots of the measurements suggested that sex did not affect the size of the thymus. Bland‐Altman plots were used to analyze intraobserver variability and showed good agreement for both of these thymic measurements for male and female fetuses. Conclusions. These results suggest that fetal sex does not affect the size of the thymus and, together with previous reports, support the hypothesis that a quantitative reduction in fetal thymus size could serve as an indirect marker of abnormal thymopoiesis and congenital thymic insufficiency.     

Abnormal Number of Fetal Ribs on 3‐Dimensional Ultrasonography

Objective. The purpose of this study was to describe the clinical importance of an abnormal number of fetal ribs. Methods. A retrospective study of all fetuses that were found to have an abnormal number of ribs during routine ultrasonographic examinations was performed. Volume data sets of the fetal ribs were acquired by either static 3‐ or 4‐dimensional volume contrast imaging in plane C. In all cases, a meticulous survey of the fetal anatomy was performed, and prenatal and postnatal records were reviewed. Results. Seventy‐five fetuses were found retrospectively to have an abnormal number of ribs. Ultrasonographic examinations were done between 14 and 31 weeks' gestation (mean, 21.8 weeks; median, 23 weeks). More than 24 ribs were found in 28 fetuses (37%), and fewer than 24 ribs were found in 47 (63%). Additional anomalies were found in 22 fetuses (29%). Cardiovascular anomalies were detected in 10 fetuses. Seven fetuses had renal anomalies. Two fetuses had mild ventriculomegaly, and 1 fetus had holoprosencephaly. Lung dysplasia was found in 2 cases. One fetus had enlarged nuchal translucency with wormian bones. Termination of pregnancy was performed in 3 cases because of major malformations. The other 19 fetuses with associated abnormalities and the 53 without associated anomalies were born alive with only minor anomalies. Conclusions. An abnormal number of fetal ribs is an isolated finding in most cases. It may also be seen with major anomalies; however, more frequently the anomalies are minor, and the overall prognosis is good.     

Three‐Dimensional Sonography of Placental Mesenchymal Dysplasia and Its Differential Diagnosis

Objective. Placental mesenchymal dysplasia (PMD) is an uncommon vascular anomaly of the placenta characterized by mesenchymal stem villous hyperplasia. Its main sonographic feature is a thickened placenta with hypoechoic areas, and an accurate sonographic diagnosis is challenging. The aim of this study was to report 2 cases of PMD and discuss the differential diagnosis of its sonographic features. Methods. Cases of placental masses were studied by 2‐dimensional (2D), 3‐dimensional (3D), and color Doppler imaging. Results. In case 1, a thick placenta with multiple hypoechoic areas was noted at 13 weeks' gestation. At 19 weeks, the multicystic area, clearly demarcated from a normal‐looking placenta, measured 6.5 × 8.5 cm and enlarged gradually. The patient gave birth to a 625‐g female neonate after spontaneous labor at almost 26 weeks' gestation. In case 2, a first sonographic examination at 25 weeks' gestation revealed a thickened placenta with hypoechoic areas and a fetus with a single umbilical artery and a ventricular septal defect. At 27 weeks, the abnormal area of the placenta measured 14.5 × 7.5 cm. At 32 weeks' gestation, a caesarean delivery was performed because of a nonreassuring fetal heart tracing, and a 1415‐g female neonate was delivered. Both cases were evaluated by 2D, 3D, and color Doppler imaging, and the pathologic features of both placentas were consistent with PMD. Conclusions. Placental mesenchymal dysplasia should be considered in the differential diagnosis of every placental mass, especially in cases of multicystic placental lesion with lack of high‐velocity signals inside the lesion, and a normal karyotype.     

Difficulties in the prenatal diagnosis of microcephaly.

Our objective was to determine whether the diagnosis of microcephaly present at birth is apparent using standard biometry in the second trimester. Fetuses with prenatally suspected microcephaly (biparietal diameter > or = 3 standard deviations below mean) who had a first sonogram prior to 22 weeks' gestation and a confirmation of microcephaly after birth were included in the study. We excluded all fetuses who had neural tube defects or other major associated abnormality that would lead to a suspicion of microcephaly. We therefore included fetuses who either had normal-appearing brains sonographically or intracranial calcifications as the only sonographic abnormality seen prior to 22 weeks' gestation. Seven fetuses met these criteria. One fetus was diagnosed as having microcephaly prior to 22 weeks' gestation. The other six fetuses had a normal head size prior to 22 weeks' gestation and were diagnosed as having microcephaly at 27 weeks' gestation and later. Only one of the seven fetuses had a karyotypic abnormality. We conclude that the prenatal diagnosis of microcephaly is not excluded by normal biometry on second trimester sonography.     

Sonographic diagnosis of fetal intestinal volvulus with ileal atresia: A case report

Fetal intestinal volvulus is a rare life‐threatening condition usually manifesting after birth with most cases being associated with intestinal malrotation. It appears on prenatal sonography (US) as a twisting of the bowel loops around the mesenteric artery, leading to mechanical obstruction and ischemic necrosis of the bowel. We report a case of intrauterine intestinal volvulus with ileal atresia, suspected when US revealed a typical “whirlpool” sign at 37 weeks' gestation, with a segment of markedly distended bowel loops and small amount of fetal ascites. © 2012 Wiley Periodicals, Inc. J Clin Ultrasound 2013     

A Thai Reference for Normal Fetal Nasal Bone Length at 15 to 23 Weeks' Gestation

Objective. The purpose of this study was to establish a Thai reference for normal fetal nasal bone length at 15 to 23 weeks' gestation. Methods. The fetal nasal bone was measured by sonography in 295 pregnant women at 15 to 23 weeks' gestation from May to August 2005. One of the first 4 authors performed 3 measurements for each woman when the fetus was in the midsagittal plane and the nasal bone was close to a 45° or 135° angle to the ultrasound beam. All neonates were examined after delivery to confirm an absence of congenital abnormalities. Results. The median nasal bone length increased by gestational age from 3.6 mm at 15 weeks to 7.3 mm at 23 weeks in a linear relationship. The fifth percentile nasal bone lengths were 2.5, 3.04, 3.28, 3.64, 4.21, 4.82, 5.69, and 6.13 mm at 15, 16, 17, 18, 19, 20, 21, and 22 weeks, respectively. The median time for measurement was 5 minutes. Conclusions. The nasal bone length in Thai fetuses at 15 to 23 weeks was found to be on average shorter than that in white and African American fetuses.     

Transient Distention of Right Posterior Located Sigma,a New Sonographic Sign for the Prenatal Diagnosis of Anal Atresia

We describe a new sonographic sign for the detection of anal atresia in the early midtrimester on transvaginal sonography. In six cases of fetal anal atresia, the finding of a transient, distended, and right‐sided sigmoid colon was observed at 13–16 weeks' gestation. Three cases have undergone pregnancy termination due to multiple anomalies. In the other three, the colonic distension resolved by 19 weeks' gestation. In two of these, the finding was isolated, and no other anomalies were detected. In all six cases, anal atresia or cloaca was confirmed on postabortal autopsy or after delivery. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45 :160–162, 2017     

Ontogeny of adrenal steroid biosynthesis: why girls will be girls

Male and female external genitalia appear identical early in gestation. Testosterone exposure at 8-12 weeks' gestation causes male differentiation. Female fetuses virilize if their adrenals secrete excessive levels of androgens, as occurs in congenital adrenal hyperplasia due to 21-hydroxylase deficiency. This can be ameliorated by administering dexamethasone to the mother. A study by Goto et al. in this issue of the JCI provides a rationale for this treatment by demonstrating that the fetal hypothalamic-pituitary-adrenal axis is fully functional when the genitalia differentiate (see the related article beginning on page 953). Dexamethasone suppresses this axis, reducing abnormal secretion of adrenal androgens. Their results also show that cortisol synthesis by the fetal adrenal decreases after this period, allowing the adrenal to secrete high levels of dehydroepiandrosterone, an androgen precursor. However, this does not virilize female fetuses because androgens are aromatized to estrogens in the placenta. Thus normal sexual differentiation requires exquisite timing of fetal cortisol and androgen secretion versus placental capacity for aromatization.     

Volume of Preclinical Xenograft Tumors Is More Accurately Assessed by Ultrasound Imaging Than Manual Caliper Measurements

Objective. The volume of subcutaneous xenograft tumors is an important metric of disease progression and response to therapy in preclinical drug development. Noninvasive imaging technologies suitable for measuring xenograft volume are increasingly available, yet manual calipers, which are susceptible to inaccuracy and bias, are routinely used. The goal of this study was to quantify and compare the accuracy, precision, and inter‐rater variability of xenograft tumor volume assessment by caliper measurements and ultrasound imaging. Methods. Subcutaneous xenograft tumors derived from human colorectal cancer cell lines (DLD1 and SW620) were generated in athymic nude mice. Experienced independent reviewers segmented 3‐dimensional ultrasound data sets and collected manual caliper measurements resulting in tumor volumes. Imaging‐ and caliper‐derived volumes were compared with the tumor mass, the reference standard, determined after resection. Bias, precision, and inter‐rater differences were estimated for each mouse among reviewers. Bootstrapping was used to estimate mean and confidence intervals of variance components, intraclass correlation coefficients (ICCs), and confidence intervals for each source of variation. Results. The average deviation from the true volume and inter‐rater differences were significantly lower for ultrasound volumes compared with caliper volumes (P = .0005 and .001, respectively). Reviewer ICCs for ultrasound and caliper measurements were similarly low (1%), yet caliper volume variance was 1.3‐fold higher than for ultrasound. Conclusions. Ultrasound imaging more accurately, precisely, and reproducibly reflects xenograft tumor volume than caliper measurements. These data suggest that preclinical studies using the xenograft burden as a surrogate end point measured by ultrasound imaging require up to 30% fewer animals to reach statistical significance compared with analogous studies using caliper measurements.     

Application of 3‐Dimensional Ultrasonography to Imaging the Fetal Anal Canal

Objective. Ultrasonography has been applied previously to the assessment of the fetal anal canal. We aimed to examine the potential of 3‐dimensional ultrasonography (3DUS) in the evaluation of the fetal anal canal and to obtain normal fetal anal canal measurements. Methods. Patients were recruited from an unselected population of gravidas with known gestational age (by dates or first‐trimester ultrasonography) and without known fetal anomalies presenting for fetal evaluation in the ultrasound units of 2 tertiary care centers between 16 and 39 gestational weeks. In addition to the ordered scan, 3DUS imaging of the fetal anal canal was performed. Transverse and sagittal views and volumes were obtained. Measurements of the fetal anal canal anteroposterior diameter, lateral diameter, and length were performed in transverse and sagittal planes, respectively, and scatterplots of these dimensions were created. Measurements were performed and repeated on raw data sets by 2 independent observers, and the results were analyzed to estimate interobserver and intraobserver reliability. Results. A total of 186 patients were examined for this study at 16 to 39 weeks' gestation (mean, 27.4 weeks). The anteroposterior diameter of the fetal anal canal in this study group ranged from 4 to 21 mm (mean, 11.2 mm; SD, ±3.5 mm), whereas the lateral diameter ranged from 7 to 18 mm (mean, 9.1 mm; SD, ±3.0 mm). The length of the fetal anal canal in this study group ranged from 3 to 24 mm (mean, 14.3 mm; SD, ±3.8 mm). Conclusions. Ultrasonographic assessment of the fetal anal canal with 3DUS is feasible. Scatterplots were created for internal anal sphincter width and length measurements from 16 to 39 weeks' gestation. Larger studies are necessary to establish nomograms of these measurements and their application to the evaluation of pathologic cases. We speculate that 3DUS assessment of the fetal anal canal may improve detection rates of disorders involving this system.