Objective: To present two-dimensional/three-dimensional (2D/3D) SlowflowHD features of the fetal duplex kidney. Case description: Two fetal unilateral duplex kidneys at 30 and 32⁺³ weeks were identified between February 2023 and January 2024. Lengths of both kidneys were >95th percentile of the reference ranges of the normal fetal kidney. Two separate noncommunicating renal pelvises (RP) were evident by 2D sonography and HDlive silhouette. 2D/3D SlowflowHD clearly showed perihilar renal arterial branching and characteristic bridge vessels between the upper renal moiety and lower kidney. Conclusion: SlowflowHD may provide novel and unique vascular information on fetal renal anomalies such as the duplex kidney.

We present hairpin curve tortuous ascending aorta of the fetus using radiant flow and HDlive flow. In a fetus with cystic hygroma and ductus venosus reverse flow at 12 weeks and 6 days of gestation, hypoplastic right ventricle and enlarged right atrium with significant tricuspid regurgitation were noted, and hairpin curve tortuous ascending aorta was evident using radiant flow and HDlive flow. At 17 weeks and 5 days of gestation, chromosome analysis showed Miller–Dieker syndrome [46XY, del(17)(p13.1)]. In another fetus at 21 weeks of gestation, hairpin curve tortuous ascending aorta and dilated pulmonary artery were identified using radiant flow. HDlive flow clearly revealed hairpin curve tortuous ascending aorta, dilated pulmonary artery, and cervical aortic arch. There were no obvious phenotypic features of connective-tissue disorder or other malformation. Tortuous ascending aorta and cervical aortic arch were confirmed after birth. To the best of our knowledge, this might be the first report of hairpin curve tortuous ascending aorta of the fetus with no obvious phenotypic features of connective-tissue disorder.

Endometrial cancer (EC) is the fourth most commonly diagnosed malignancy in the world. The first symptom of endometrial carcinoma usually is postmenopausal bleeding, but only about 10–15% of women presenting with postmenopausal bleeding will actually have EC, and a definitive diagnosis needs histological proof. Ultrasonography is a useful tool for detecting endometrial pathology in everyday practice. To optimize the sonographic assessment of endometrial tumors, a better understanding of the association between sonographic features and tumor stage, grade, and histological type is needed. Three-dimensional (3D) ultrasonography is a new imaging technique that has become currently available in gynecologic practice, specifically in gynecologic oncology. In addition, 3D/four-dimensional (4D) power Doppler ultrasonography allows a 3D reconstruction of the vascular network and also calculates vascular indices based on the total and relative amount of power Doppler information within the volume of interest. Accurate clinical staging of EC not only reduces complications caused by inadequate or overtreatment but is also a guarantee for the retention of fertility in young patients.

Rhabdomyoma is the most common fetal cardiac tumor accounting for 60–65% of all fetal tumors and up to 90% of cardiac tumors in pediatric population. Rhabdomyomas are benign lesions and the symptoms depend on the size and location of the rhabdomyomas. A single or multiple lesions are usually located within the left ventricle and projecting into the ventricular cavity or moving freely as a pedunculated mass. Intracavitary growth may cause ventricular outflow tract obstruction, valvular compromise, and disruption of intracardiac blood flows, leading to congestive heart failure. Rhabdomyomas >30 mm in diameter, regardless of number and location, are associated with postnatal arrhythmia. Cardiac rhabdomyoma is associated with tuberous sclerosis in about 50–90% of cases. Rhabdomyomas can be detected as early as the second trimester by echocardiography which is the primary diagnostic tool for the evaluation of cardiac tumors. They usually grow until 32 weeks gestation due to the transmission of maternal estrogens to the fetus, and then gradually regress. When cardiac rhabdomyoma is suspected on fetal echocardiography, it is important to check the kidneys and brain for tuberous sclerosis complex (TSC)-specific lesions. The prognosis depends on the number, size, and location of the tumors, as well as the presence or absence of associated anomalies. Rhabdomyomas, single or multiple, in the majority of cases, are not hemodynamically relevant and regress in infancy. Expectant management is the recommended approach, and neonatal management is always preferred when lung maturity is assured. Prenatal therapy is recommended only in case of severe fetal hemodynamic deterioration, hydrops, or uncontrollable arrhythmias.

Hydrops fetalis is defined as the accumulation of fluid with or without edema involving at least two fetal components. About 10% of cases are due to maternal hemolytic antibodies, that is, immune hydrops, while 90% of cases are nonimmune. Nonimmune hydrops fetalis (NIHF) is a heterogeneous condition that may be secondary to over 100 conditions, the cardiovascular causes are the most common. A significant percentage of cases will still not have an identifiable cause even after postnatal evaluation. Sonographic features include increased amniotic fluid volume, increased nuchal translucency, placentomegaly, fetal pleural or pericardial effusion, generalized fetal body swelling, and umbilical venous dilatation. Once the diagnosis of NIHF has been established, scans should be performed every 2–3 weeks to monitor the evolution of hydrops, and every effort should be made to identify the underlying cause. The treatment of nonimmune hydrops is determined by the gestational age (GA) at which the diagnosis is made, as well as the ability to identify the cause of the NIHF. Delivery should be done at a tertiary care hospital for appropriate neonatal interventions. Timing and method of delivery depend on the cause of hydrops. Preterm delivery is recommended only for obstetric indications including the development of “mirror syndrome.” The prognosis is dependent on the underlying cause and onset of NIHF. Progressive unexplained hydrops is often lethal before or soon after birth with an overall mortality of 50–90%. NIHF secondary to treatable causes such as fetal arrhythmia, chylothorax, or infection with parvovirus B19 has a better survival rate.

Preoperative diagnosis of endometrial pathology is essential for the outcome of treatment. It is important to preoperatively detect the malignant potential of changes and choose an adequate therapeutic approach. This is especially important for women who have not completed their reproduction in terms of choosing minimally invasive operative methods and preserving their fertile potential. It is very important to optimize the preoperative ultrasound examination of endometrial tumors concerning the differential diagnosis of an endometrial benign and malignant lesion, as well as the type of tumor, and to assess the degree of myometrial invasion of malignant lesions. The performance of the use of three-dimensional/four-dimensional (3D/4D) ultrasound in diagnostics, especially in the analysis of certain endometrial pathologies, has already been established and provides very useful information. However, the morphological and vascular characteristics might correlate with tumor stage, grade, and size, and that information could be of benefit in the assessment of the preoperative tumor and perhaps be used in risk evaluation in the future. Exploratory curettage and pathohistological findings of endometrial pathology are the gold standard, but in some cases, even these methods, which depend on several variables, do not provide a definitive, accurate diagnosis. This is why, in combination with new ultrasound techniques, the effectiveness of preoperative diagnosis of pathological changes in the endometrium increases.

Three-dimensional (3D) ultrasound offers the possibility of studying the fetal face in a more global way than conventional two-dimensional (2D) ultrasound. In normal cases, the images obtained help to transmit a feeling of calmness to the parents and reinforce the affective bonds with their child. In pathological cases, 3D ultrasound can help parents and other doctors involved to take a more realistic view of the problem. It is expected that the use of this technology will provide parents with the knowledge to have a better judgment while taking decisions.

Triploidy and monosomy X (Turner syndrome) are the two most common chromosomal anomalies at conception. Their prevalence decreases with increasing gestational age (GA), and they are relatively rare at birth. These genetic conditions can be prenatally or postnatally detected by karyotyping [chromosome analysis of fetal cells collected by chorionic villous sampling (CVS) or amniocentesis or blood lymphocytes]. Triploidy is caused by a complete extra set of chromosomes (the presence of 69 chromosomes). If the extra set of chromosomes is maternal in origin, the disease is called digynic triploidy, while if the extra set of chromosomes is paternal in origin, the disease is called diandric triploidy. Triploidy is lethal, most affected embryos are miscarried; however, some individuals survive a few hours or days after birth. Turner syndrome is an aneuploidy (monosomy X) in which only one chromosome X is present, and the other sex chromosome is either absent or abnormal. Severe forms of Turner syndrome present major fetal anomalies, including fetal hydrops and usually progress to early fetal demise (the lethal Turner phenotype). Postnatally, Turner syndrome presents as a form of primary ovarian insufficiency, determined by a gonadic digenesis (not by agenesis). Both triploidy and Turner syndrome must be taken in consideration if sonography reveals minor or major abnormalities in the first or second trimester of pregnancy. Active screening in the general pregnant population is not justified for these conditions alone. Both conditions can be diagnosed prenatally in individual cases.

Skeletal dysplasias are a heterogeneous group of bone growth disorders resulting in abnormal shape and/or size of the skeleton involving bone and cartilage structures. The current classification is based upon either descriptive findings or the presumed pathogenesis of the disease. The classification system most commonly used is the International Nomenclature and Classification of Constitutional Disorders of Bone. There are now over 33 osteochondrodysplasias groups and 3 genetically determined dysostoses. The prevalence of skeletal dysplasias identified at birth is approximately 2.4/10,000 births. The overall frequency of skeletal dysplasias among perinatal deaths is approximately 9.1/1000. While more than 200 different skeletal dysplasias have been described, the number that can be recognized by ultrasound in the antenatal period is far fewer. The antenatal diagnosis of skeletal dysplasia can be difficult. The challenge involves not only accurately identifying the fetus affected with an abnormal skeleton but also accurately diagnosing the skeletal abnormality and predicting the fetal outcome. The majority of skeletal dysplasias are diagnosed after the first trimester. Approximately 50% will be diagnosed prior to 24 weeks. The accurate antenatal diagnosis of skeletal dysplasias is good at 60--65%, with approximately 19% being missed diagnosed, in 21% the diagnosis was imprecise. Ultrasound can be a valuable tool not only in identifying the potentially affected fetus but also in counseling the parents regarding the potential outcome and options for pregnancy management.

Gastrointestinal tract and internal abdominal wall malformations are infrequent malformations. Their global incidence is estimated to be below three to six cases in every 1,000 newborns, although it is probably higher, since many of them are part of very severe multiple malformations syndromes, with a high incidence of intrauterine death even in early stages of pregnancy. They are often associated with polyhydramnios, which is in 10% associated with upper digestive atresias, and in another 10% with lower digestive atresias. Colon atresia is responsible of 5–10% of all the intestinal atresias with most frequent anal atresia occurring in around 1 in every 5,000 live births. Many other fetal intestinal disorders have been described by ultrasound including small intestine or anorectal atresia, Hirschsprung's disease, megacolon with anourethral atresia, and distended and descended colon, which is associated with Johanson–Blizzard syndrome. It is important to diagnose possible malformations in other organs and systems that may be related to these defects and therefore, will determine the neonatal prognosis. These anomalies are diagnosed by two-dimensional (2D) ultrasound assessment, many of them even in the first trimester, but three-dimensional (3D) and four-dimensional (4D) ultrasound is a remarkable advance in a better definition of the defect.

Conjoined twins have an estimated prevalence between one in 50,000 and one in 1,00,000 births. Prenatal two- and three-dimensional (2D and 3D) real-time ultrasonography is the most reliable method for establishing a prenatal diagnosis and detecting associated anomalies. Recent improvements in ultrasonography have made early diagnosis of conjoined fetuses in the first trimester possible. Most cases of conjoined twins occur in monochorionic monoamniotic pregnancies, making sonographic identification of distinct placentae and/or intervening amniotic membrane(s) a criterion to exclude fetal conjunction. There are two opposing pathogenetic theories, supporting fission vs fusion of embryos in the early first trimester. In very rare cases of diamniotic monochorionic conjoined twins, a distinct pathogenetic mechanism of conjoined twinning, similar to that of body stalk anomaly may exist. Prenatal diagnosis of conjoined fetuses is essential for further management. Parents need detailed counseling in order to decide among various management options—(1) pregnancy continuation and scheduled neonatal surgery, (2) termination of pregnancy, and (3) multifetal pregnancy reduction or selective fetocide in cases of high-order multifetal pregnancies with a component of conjoined fetuses. Pre- and postnatal management is challenging, and an interdisciplinary medical team involving obstetricians, neonatologists, pediatric surgeons, and anesthetists should carefully approach and assist parents in their decisions. In special cases, additional consultation by specialized centers in other countries may be needed. Furthermore, adequate psychosocial support should be offered, and palliative care services should be available in selected cases.