The Development of Normal Fetal External Genitalia Throughout Gestation.

In this review, we describe normal development of fetal genitalia throughout gestation as well as the identification of normal male and female genitalia on ultrasound. We use abnormal and ambiguous genitalia as illustrative tools to assist with the identification of normal genitalia and recognition of some of the most common abnormalities in external genitalia development.

FundAl Retroflexion (FAR) Angle is a Novel Sonographic Marker Associated With Cesarean Scar Pregnancies in the First Trimester: A Case-Control Study.

OBJECTIVES: Early diagnosis of Cesarean scar pregnancies (CSP) remains difficult. This study describes a novel sonographic marker, the FundAl Retroflexion (FAR) angle, that may be used in the first trimester. The objective of the study is to compare the FAR angle between CSP and normal pregnancies. METHODS: For this case-control study, we reviewed images from our institution's database that were acquired from January 2016 to December 2019. All cases of CSP and randomly selected controls, defined as patients with history of Cesarean delivery and normal implantation, that underwent ultrasound evaluation at <14 weeks were included. The FAR angle, defined as the acute angle created between the endometrial echo and cervical canal, was measured. The mean FAR angle was then compared between the two groups and a receiver operating characteristic (ROC) curve was generated. RESULTS: We identified 15 cases of CSP during the study period and were able to measure the FAR angle in 14 of the cases. The mean FAR angle was larger in CSP than in normal control pregnancies (45° versus 27°, respectively, P < 0.001). Using an ROC curve, a FAR angle cut off of 40° maximizes the ability to distinguish between CSP from normal pregnancies. CONCLUSIONS: The FAR angle provides an easily obtainable and numerical measurement. CSP have larger FAR angle compared to normal controls with a distinguishing cut off of 40°. Larger studies are needed to determine if using the FAR angle can improve first trimester diagnosis for CSP.

What Are the Double Lines of the Fetal Cavum Septi Pellucidi on Ultrasound?

OBJECTIVE: To demonstrate the significance of the double line appearance of the septi pellucidi laminae (SPL) on fetal ultrasound. METHOD: A total of 522 uncomplicated singleton pregnancies (15 to 39 weeks' gestational age) with fetal ultrasounds were enrolled. The presence of a single versus double line SP as well as measurement of the cavum septi pellucidi (CSP) was determined retrospectively. Ultrasound settings from the CSP images were recorded. Thickness of the SPL was measured in 20 ultrasound and 14 MRI cases; histology was reviewed from one neonate. Maternal BMI and gestational age were also recorded. RESULTS: The presence of double line SPL is a normal sonographic finding, seen in 47% (188/403) of normal fetuses. Thickness of the SPL in 10 cases with double line averaged 1.4 mm and in 10 cases with single line averaged 0.8 mm; MRI measurements were within 0.1 mm of the corresponding ultrasound measurements. Double line cavum was more often seen with mid-dynamic contrast range settings (5, 6) rather than high range settings (7-10) (P value <.05). The double line was only visualized on ultrasound when the angle of insonation was at or near perpendicular to the laminae; it was never visualized on coronal ultrasound imaging or MRI imaging. CONCLUSION: A double line septum pellucidum lamina is a normal finding seen in almost 50% of uncomplicated singleton pregnancies. It may be attributed to borders of cell layers within each lamina that form separate specular reflections on both sides; this can be accentuated by ultrasound settings and beam angulation.

Ultrasound and Magnetic Resonance Imaging of Agenesis of the Corpus Callosum in Fetuses: Frontal Horns and Cavum Septi Pellucidi Are Clues to Earlier Diagnosis.

OBJECTIVES: We hypothesized that: (1) fetal frontal horn (FH) morphology and their proximity to the cavum septi pellucidi (CSP) can assist in suspecting complete agenesis of the corpus callosum (cACC) and partial agenesis of the corpus callosum (pACC) earlier than known indirect ultrasound (US) findings; (2) FHs assist in differentiating a true CSP from a pseudocavum; and (3) magnetic resonance imaging (MRI) is useful in learning FH morphology and pseudocavum etiology. METHODS: Thirty-two patients with cACC and 9 with pACC were identified on an Institutional Review Board-approved retrospective review. Of the 41 cases, 40 had prenatal US, and 21 had prenatal MRI; 17 had follow-up neonatal US, and 14 had follow-up neonatal MRI. Variables evaluated retrospectively were the presence of a CSP or a pseudocavum, ventricle size and shape, and FH shape (comma, trident, parallel, golf club, enlarged, or fused). Displacement between the inferior edge of the FH and the midline or cavum/pseudocavum was measured. RESULTS: Fetal FHs had an abnormal shape in 77% ≤20 weeks' gestation, 86% ≤24 weeks, and 90% >24 weeks. Frontal horns were laterally displaced greater than 2 mm in 85% ≤20 weeks, 91% ≤24 weeks, and 95% >24 weeks. The CSP was absent in 100% of cACC cases and 78% of pACC cases, and a pseudocavum was present in 88% of cACC cases and 78% of pACC cases across gestation. Magnetic resonance imaging confirmed US pseudocavums to be focal interhemispheric fluid or an elevated/dilated third ventricle. CONCLUSIONS: Frontal horns assist in assessing ACC ≤24 weeks and throughout gestation. Pseudocavums, often simulating CSPs, are common in ACC. Frontal horn lateral displacement and abnormal morphology, recognized by MRI correlations, are helpful in differentiating a pseudocavum from a true CSP. A normal CSP should not be cleared on screening US unless normally shaped FHs are seen directly adjacent to it.

Fetal Ultrasound and Magnetic Resonance Imaging Findings in Suspected Septo-Optic Dysplasia: A Diagnostic Dilemma.

OBJECTIVES: To investigate prenatal imaging findings supporting a diagnosis of suspected septo-optic dysplasia (SOD) by fetal ultrasound (US), magnetic resonance imaging (MRI), or both. METHODS: A retrospective review identified 11 patients with SOD: 9 had a clinical diagnosis of SOD postnatally, and 2 were terminated on the basis of suspicious prenatal imaging. Prenatal and neonatal imaging of the cavum septi pellucidi (CSP), frontal horns (FHs), and lateral ventricles was evaluated. RESULTS: The appearance of the CSP varied on US and MRI. Complete ("fused") FHs or partial absence of the CSP was reported in 6 of 11 patients by fetal US and 7 of 8 patients by fetal MRI. The diagnosis of SOD was prospectively suspected prenatally in 6 of 11 and in an additional 5 of 11 cases retrospectively. Fetal MRI incorrectly initially reported normal morphologic abnormalities for 2 cases with partial absence of the CSP, whereas US accurately identified the morphologic abnormalities in 1 of these cases before MRI. Imaging features were first suggested at anatomic US (4 patients) and follow-up prenatal US (2 patients). Neonatal imaging was concordant in all 9 live births: 5 completely absent CSP, 3 partially absent CSP, and 1 completely present CSP. Clinical manifestations included optic nerve hypoplasia (9 of 9), panhypopituitarism (5 of 9), and neurodevelopmental delays. CONCLUSIONS: Primary imaging features of SOD are "continuous" FHs with complete or partial absence of the CSP. Septo-optic dysplasia can be suspected in utero and can appear isolated but has substantial associated central nervous system anomalies identified on fetal MRI or after birth. Partial absence of the CSP can be a prenatal sign of suspected SOD, although fetal MRI lacked the spatial resolution to identify it accurately in all cases.

Ultrasound Measurements of Frontal Horns and the Cavum Septi Pellucidi in Healthy Fetuses in the Second and Third Trimesters of Pregnancy.

OBJECTIVES: To assess the visualization rate and size of the frontal horns (FHs) and cavum septi pellucidi (CSP) in healthy fetuses throughout pregnancy. METHODS: After Institutional Review Board approval, 522 consecutive uncomplicated singleton pregnancies between 15 and 39 gestational weeks were enrolled in the study. Ultrasound measurements of the anterior horn width (AHW), center from the horn distance (CFHD), distance from the FHs to the CSP, and CSP width were retrospectively performed using axial transventricular or transcerebellar planes. Available maternal body mass indices were recorded. RESULTS: At least 1 FH was seen in 78% of the cases. The mean AHW decreased over the second trimester and plateaued in the third trimester. The CFHD plateaued in the second trimester and increased in the third trimester. Downside FHs were generally larger than upside FHs. More FHs were measured in transventricular (69%) than transcerebellar (31%) planes. Frontal horns were seen with high, low, and no confidence in 57%, 21%, and 22% of cases, respectively. No-confidence rates were 17% in the second trimester and 42% in the third trimester. The CSP was not visualized in 4% of cases; 15 of 19 cases of a nonvisualized CSP were scanned between 18 and 37 weeks. Mean body mass indices ± SDs were 27.6 ± 6.7 kg/m2 for the patients in cases of a visualized CSP and 32.4 ± 9.1 kg/m2 for the patients in cases of a nonvisualized CSP. CONCLUSIONS: Normative data for the fetal FH and CSP width were established. Frontal horns are more frequently seen on transventricular views and are difficult to confidently assess in the late third trimester. This study challenges previously reported data that the CSP is seen in 100% of cases from 18 to 37 weeks.

The Fetal 3-Vessel Views: An Illustrative Case-Based Tutorial.

In 2018, the American Institute of Ultrasound in Medicine revised its obstetric Practice Parameter for the second-trimester fetal anatomic survey. The 2018 Practice Parameter recommends incorporation of the 3-vessel view and 3-vessel and trachea view "if technically feasible." Sonographers and other medical providers may require additional training and education to develop greater proficiency in obtaining and interpreting these views. This pictorial essay, including ultrasound images alongside their respective schematic diagrams, provides an up-to-date, practical, and clinically oriented review of the 3-vessel view and 3-vessel and trachea view and their most common presentations in the context of congenital heart disease.

Whole-exome sequencing reveals novel USP9X variant in female fetus with isolated agenesis of the corpus callosum.

Whole-exome sequencing in a female fetus detected a USP9X variant. This X-linked gene was recently associated with intellectual disability and distinct pattern of malformation in females. Isolated agenesis of the corpus callosum has not been reported in association with USP9X. Identifying this variant impacted management of the subsequent pregnancy.

Detailed Fetal Anatomic Ultrasound Examination: Effect of the 2014 Consensus Report on a Tertiary Referral Center.

This study evaluates the impact of extended cardiac views on examination time, repeat imaging, and anomaly detection before and after implementation of 76811 guidelines (American Institute of Ultrasound in Medicine Consensus 2014). It is a retrospective study of singleton pregnancies undergoing detailed ultrasound imaging at 18 weeks' gestation or greater before and after the protocol change in an academic, tertiary care fetal center. Views required prior to 2014: 4-chamber, left outflow tract, right outflow tract. Additional views required after 2014: bicaval, aortic arch, 3-vessel, and 3-vessel trachea. Fetuses with known anomalies were excluded. Rates of detection of congenital heart disease (CHD), examination completion, repeat examination recommendation, fetal echocardiogram recommendation, completion by body mass index, and cardiac examination time were determined. Six hundred twenty-four subjects were included, 217 before and 407 after protocol change. Views obtained were as stated in the American Institute of Ultrasound in Medicine/Society for Maternal-Fetal Medicine consensus. Detection of CHD was not improved. Examination times increased by 20% (6.4 vs 7.7 minutes, P < 0.05). Number of incomplete studies increased by 130% (11% to 26%, P < 0.05). Twice as many patients were referred for repeat examination (6% vs 13%, P < 0.05). Completion rates were negatively correlated with body mass index. Recommendations for fetal echocardiogram were unchanged (5% vs 6%, P = 0.6). Additional imaging did not increase detection rate of CHD (3% vs 2%, P = 0.3). Extended cardiac views resulted in increased examination time, more incomplete examinations, and more repeat examinations without changing detection rates of CHD.

Ultrasonographic prenatal imaging of fetal ocular and orbital abnormalities.

Technological progress in medicine has provided earlier diagnosis, even into the prenatal period. We address ultrasonographic imaging of the prenatal eye and orbit. During development of these structures, multiple pathologies and diseases can arise. Orbital anomalies can be detected prenatally using ultrasound or magnetic resonance imaging. Some of these include congenital cataracts, hypertelorism, hypotelorism, dacryocystocele, microphthalmia, anophthalmia, orbital tumors/masses, and septo-optic dysplasia. We describe characteristic ultrasound findings of these diseases. Prenatal ocular and orbital diagnosis is best facilitated by a team approach between ophthalmology, radiology, obstetrics, neonatology, and genetic counselors to optimize diagnostic accuracy, familial expectations, and early treatment.

A fetal diagnostic center's referral rate for perinatal palliative care.

BACKGROUND: Fetal specialists support standardizing the practice of offering women palliative care for life limiting fetal diagnoses. However, there is little data available regarding what fetal specialists do in practice. Since 2003, our center has kept a database of all women referred for fetal complications. METHODS: Retrospective electronic chart review of pregnant women between 2006 and 2012 using UCSD's Fetal Care and Genetics Center referral database. Objectives were to determine: (I) how many high risk pregnancies referred to the University of California San Diego Medical Center (UCSD) over a 6-year period have potentially life limiting fetal diagnoses; (II) pregnancy outcome; and (III) referral rate to perinatal palliative care. RESULTS: Between July 2006 and July 2012, 1,144 women were referred to UCSD's Fetal Care and Genetics Center, a tertiary care center. Of that cohort, 332 women (29%) were diagnosed prenatally with a potentially life limiting fetal diagnosis. Most women were Hispanic or Latino, married, and had previous children. The median gestation at confirmed diagnosis was 19 weeks. Trisomy 13, Trisomy 18, and anencephaly comprised 21% of cases. The pregnancy outcome was determined in 95% cases: 56% therapeutic abortion, 16% intrauterine fetal demise, and 23% live birth. Only 11% of cases were referred to perinatal palliative care. CONCLUSIONS: The vast majority of women with potentially life limiting fetal diagnoses are not referred to perinatal palliative care. Evaluation of how to integrate palliative care into high-risk obstetrics is needed.

Enlarged Cavum Septi Pellucidi and Vergae in the Fetus: A Cause for Concern.

OBJECTIVES: To investigate fetal cases identified at our institution to determine whether an enlarged cavum septi pellucidi or cavum vergae is associated with other fetal abnormalities and whether its presence warrants more detailed investigation of the fetus. METHODS: In a retrospective study, 15 high- and low-risk patients undergoing prenatal sonography who had an enlarged cavum septi pellucidi or cavum vergae identified were reviewed. Data were collected for the sonographic study indication, gestation age at diagnosis of a prominent cavum, and associated anomalies. Follow-up outcome data regarding further imaging, karyotype, diagnosis of brain anomaly, and associated congenital abnormalities were obtained. RESULTS: Fifteen patients met the inclusion criteria. Nine patients were identified as having a prominent cavum septi pellucidi, and 6 were identified as having a prominent cavum vergae. The mean gestational age ± SD was 22.7 ± 5.9 weeks. Eleven patients made it to delivery. Of the 15 patients, 4 were thought to have trisomy 21, and 13 had congenital anomalies. Outcomes included 10 major adverse outcomes, 4 cases with normal development or minor abnormalities, and 1 lost to follow-up. An isolated dilated cavum on prenatal sonography was seen in 5 cases: 1 with lissencephaly on a neonatal examination, 3 premature deliveries (1 demise, 1 hospice, and 1 normal), and 1 unknown. CONCLUSIONS: Our cohort had many associated clinical anomalies: 3 confirmed trisomy 21 and 1 probable trisomy 21, 2 genetic disorders, and 10 major adverse outcomes, 5 of which were grave. Although we studied a small cohort, we conclude that an enlarged cavum septi pellucidi or cavum vergae warrants consideration of genetic counseling, which may include noninvasive prenatal testing (cell-free DNA), amniocentesis with microarray testing, or both.

Anomalous Pulmonary Venous Return: Insights Into Prenatal Detection.

OBJECTIVES: To review all cases of total anomalous pulmonary venous return (TAPVR) or partial anomalous pulmonary venous return (PAPVR) identified prenatally or postnatally at a single institution and to identify factors that may lead to a correct or missed diagnosis in both high- and low-risk fetuses on screening examinations. METHODS: Fetal images from 16 cases of prenatally or postnatally diagnosed T/PAPVR were retrospectively reviewed to analyze factors that influenced interpretations and diagnoses. RESULTS: Sixteen diagnoses of T/PAPVR were made, with a final number of 10 confirmed cases, 1 of which was PAPVR. Ten fetuses with a presumptive diagnosis of T/PAPVR before delivery were at an average gestational age of 24.7 weeks, with 5 cases diagnosed postnatally. None of the diagnoses of isolated TAPVR were made during a screening examination. Twelve of the pregnancies were complicated by complex cardiac defects, including 6 with heterotaxy syndromes. Of the 5 abnormal cases identified in the postpartum period, 3 had isolated TAPVR. In the 3 patients with isolated defects, prenatal echocardiography was not performed; the anatomy scan interpretations were confounded by multiple factors. In retrospect, there was no obvious sonographic evidence of TAPVR in these patients; however, color flow Doppler imaging of the pulmonary veins was not performed on any of them. CONCLUSIONS: Although fetal echocardiography has improved the overall detection of TAPVR or PAPVR, this abnormality continues to elude prenatal diagnosis during screening in both low- and high-risk patients. We hypothesize that the use of color flow Doppler imaging in the 4-chamber view may assist in diagnosing TAPVR in screening low-risk patients, especially in those with difficult scans.

Three-dimensional ultrasonographic depiction of fetal brain blood vessels.

OBJECTIVE: The objective of this study is to evaluate the fetal cerebral vasculature by three-dimensional (3D) ultrasonography and Doppler technologies in normal fetuses and to describe a systematic method for analysis of volume data sets. METHODS: 3D volumes of the fetal brain were acquired prospectively in 25 patients between 12.3 and 36.3 weeks' gestation. Volumes were acquired with high-definition Doppler flow. The feasibility of identifying the fetal cerebral blood vessels and venous sinuses was analyzed. RESULTS: A step-by-step systematic approach to identify the cerebral vasculature from ultrasonographic volume data sets was developed. The volumes were rotated into a standard anatomic orientation in the multiplanar display, and then, by systematic navigation, the vessels were demonstrated. Arteries of the circle of Willis, basilar artery, pericallosal artery, and internal carotid arteries were demonstrated in more than half of the fetuses. Tiny vessels such as those that supply the cerebellum and those that branch from the pericallosal artery were demonstrated in less than 50% of the volumes. CONCLUSIONS: The essential fetal cerebral vessels can be visualized by 3D volume analysis. Systematic analysis enables identification of the fetal brain arteries, veins, and sinuses and provides knowledge about anatomical variations and the diversity of human anatomy. © 2016 John Wiley & Sons, Ltd.

Evaluation of Fetal First and Second Cervical Vertebrae: Normal or Abnormal?

OBJECTIVES: To use 3-dimensional sonographic volumes to evaluate the variable appearance of the normal fetal cervical spine and craniocervical junction, which if unrecognized may lead to misdiagnosis of malalignment at the first and second cervical vertebrae (C1 and C2). METHODS: Three-dimensional sonographic volumes of the fetal cervical spine were obtained from 24 fetuses at gestational ages between 12 weeks 6 days and 35 weeks 1 day. The volumes were reviewed on 4-dimensional software, and the vertebral level was determined by labeling the first rib-bearing vertebra as the first thoracic vertebra. The ossification centers of the cervical spine and occipital condyles were then labeled accordingly and evaluated for alignment and structure by rotating the volumes in oblique planes. The appearance on multiplanar images was assessed for possible perceived anomalies, including malalignment, particularly at the C1 and C2 levels. Evidence of head rotation was correlated with the presence of possible malalignment at C1-C2. Head rotation was identified in the axial plane by measuring the angle of the anteroposterior axis of C1 to the anteroposterior axis of C2. RESULTS: Of the 24 fetuses, 16 had adequate quality to assess the entire cervical spine and craniocervical junction. All 16 cases showed an osseous component of C1 that did not align directly with C2 on some of the multiplanar images when the volumes were rotated, which could lead to suspected diagnosis of spinal malalignment or a segmental abnormality, as occurred in 2 clinical cases in our practice. All 16 cases showed at least some degree of head rotation, ranging from 2° to 36°, which may possibly explain the apparent malalignment. The lateral offset from C1 to C2 ranged from 0.0 to 3.3 mm. CONCLUSIONS: The normal C1 and C2 ossification centers may appear to be malaligned due to normal offsetting (lateral displacement) of C1 on C2. An understanding of the normal development of the cervical spine is important in assessing spinal anatomy.

Ultrasound Evaluation of Primary Alveolar Grafting in Cleft Lip/Palate Treatment: Development of a Novel Sonographic Grading System.

OBJECTIVE: To explore ultrasonographic evaluation of primary alveolar repair in cleft lip/palate patients and develop a grading system to assess outcomes of graft success. DESIGN: Sixteen patients with an average age of 2 years 1 month had sonograms performed at various points in their treatment to determine the feasibility of ultrasound in visualizing alveolar bone defects and changes over time postgrafting. A total of 23 sonograms were performed: 21 at an average of 12 months postoperatively and 2 at an average of 1 month preoperatively. MAIN OUTCOME MEASURES: A 10-point grading system was developed assessing three categories: locations of lateral bone bridging across the cleft, quantification of residual defects with air or fluid channels, and locations of calcification. Three operators graded 10 sonograms to assess interobserver reliability, and the scores were also validated against dental radiographs in patients old enough for radiographic imaging. RESULTS: Linear weighted kappa statistics revealed substantial interobserver agreement for total scores, with an average kappa value of .708. In limited patients with radiographs, a total score of 9/10 correlated with a Chelsea score of 6.5/8 and category A. CONCLUSIONS: Sonographic evaluation, coupled with this novel grading system, shows potential for early assessment of outcomes of graft success when evaluating new techniques of primary alveolar grafting.

Placental Sonolucencies in the First Trimester: Incidence and Clinical Significance.

OBJECTIVES: The aims of this study were to determine the incidence of placental sonolucencies on first-trimester screening sonograms in a general obstetric population and assess whether these findings are associated with adverse obstetric outcomes. METHODS: A retrospective cohort analysis of 201 pregnant patients screened at a high-risk prenatal diagnostic center was conducted with first-trimester cine clips reviewed by 2 radiologists. Placental sonolucencies were defined as intraplacental anechoic or heterogeneous areas 0.7 cm or greater. Obstetric and neonatal outcomes were collected by chart review. RESULTS: Placental sonolucencies 0.7 cm or greater were seen in 45 (22.4%) of first-trimester ultrasound examinations. The ultrasonographic presence of a placenta previa, marginal sinus, and subchorionic hemorrhage was not more common in those with placental sonolucencies 0.7 cm or greater (P > 0.05). Sonolucencies were not associated with prior cesarean deliveries (P > 0.05). Both the groups with and without sonolucencies 0.7 cm or greater had similar rates of antepartum hemorrhage, preeclampsia, preterm delivery, cesarean delivery, postpartum hemorrhage, and delivery of small-for-gestational-age infants. One placenta accreta and no fetal demises occurred in the study population. CONCLUSIONS: Placental sonolucencies detected on first-trimester screening sonograms in the general obstetric population are not predictive of poor obstetric outcomes.

Setting up a Nuchal Translucency Clinic: What Radiologists Need to Know.

The purpose of this article was to discuss the process of setting up a nuchal translucency (NT) screening clinic in clinical practice, how to interpret the information in combination with other clinical tests, what to do if abnormal results are obtained, and to illustrate some of the fetal anomalies that are associated with an increased NT. The NT was initially implemented to predict the likelihood of a fetus with Down syndrome. Maternal age can be combined with fetal NT and maternal serum biochemistry (free ß-hCG and PAPP-A) at 11 to 14 weeks to identify about 90% of affected fetuses. Setting up a clinic to perform the NT screening requires certified physicians and certified sonographers. Certification can be obtained for both physicians and sonographers through Nuchal Translucency Quality Review and Fetal Medicine Foundation. Cell-free DNA testing is now altering what our patients are choosing to evaluate fetuses at risk for chromosomal anomalies and congenital anomalies. Common pitfalls to performing, interpreting, and conveying results of the NT are illustrated in this article. Nasal bone measurement, fetal anatomy examination and fetal echocardiography are tools that add sensitivity to the detection of chromosomal abnormalities. Examples of fetal anomalies discovered during the NT screening are also illustrated. Screening for obstetric complications is an additional benefit to the NT clinic.

Simplifying the ultrasound findings of the major fetal chromosomal aneuploidies.

Sonographic aneuploidy markers and structural anomalies associated with the 5 most common chromosomal aneuploidies are organized and simplified to highlight the many sonographic findings that are commonly seen with each aneuploidy. Identification of these findings allows families to have the option to pursue prenatal genetic testing to confirm or exclude chromosomal abnormalities suggested by such prenatal ultrasound findings and make informed decisions about the subsequent management of their pregnancy. We review the most common major human chromosomal aneuploidies, including trisomies 21, 18, and 13; Turner syndrome; and triploidy. The focus is on the major structural anomalies seen with each of these, as well as ultrasound markers (findings associated with increased risk of chromosomal abnormality but also seen in normal fetuses). The role of clinical information such as maternal serum screening and new cell-free fetal DNA screening is also reviewed. As patients do not usually present for fetal ultrasound with a known diagnosis, a concise knowledge of ultrasound and clinical findings will alert radiologists to concerning cases and prompt a guided search for important associated anomalies. Fetal ultrasound can be challenging owing to the many findings and sometimes technically difficult evaluation. By simplifying the ultrasound findings seen with the major chromosomal abnormalities and highlighting the role of clinical history, we hope that an informed search for specific sonographic findings can be performed; thereby, reducing missed diagnoses.