Three-dimensional ultrasound has many functions, and is a little complicated to use perfectly. But by starting from easy cases, objects and display modes in daily practice, 3D ultrasound would be a powerful diagnostic tool when and after some abnormalities are suspected with 2D ultrasound. Some tips to use 3D ultrasound easily and efficiently are demonstrated for those who are not familiar with 3D ultrasound.

After the introduction of high-frequency transvaginal transducers in clinical obstetrics, the term ‘sonoembryology’ was first coined in 1990.¹ Three-dimensional sonography performed with a transvaginal approach has expanded the depth of inquiry and allowed threedimensional sonoembryology.

Transvaginal approach combined with high frequency (12 MHz) and a harmonic phase inversion method can provide us images with high quality and high resolution demonstrating detailed embryonal structures, including normal development of embryos and fetuses, and many congenital abnormalities, such as conjoined twin from 9 weeks, vertebral abnormality from 9 weeks, cleft lip/palate from 12 weeks, congenital cataract from 14 weeks, limb abnormality from 11 weeks, thoracoabdominal abnormality from 12 weeks of gestation.

It is possible that by developing 3D neurosonoembryology imaging in utero, current fetal staging (which uses gestational age based on last menstrual period or crown-rump length measurement) may change into a ‘morphological staging system’, such as the Carnegie staging system, which has been central to embryology.

A novel imaging technique of high-resolution transvaginal 3D sonography is illustrated in the definition of normal embryonic anatomy as well as in the identification of many congenital anomalies. They allow extending the detection of anatomical congenital anomalies to an earlier gestational age.

Doppler velocimetry has recently become an informative procedure for the real-time and noninvasive evaluation in fetal hemodynamics. The analysis of flow velocity waveforms in various kinds of vessels has been made for not only clarifying fetal physiology and pathophysiology of various disorders but also for determining the most appropriate intervention from the viewpoint of the integrated management protocol. The unique change in both the arterial and venous flow in normal and compromised fetuses has been demonstrated. Clinical applications of the Doppler technique in monitoring the fetus are reviewed.

Three-dimensional (3D) ultrasound is one of the most attractive modality in the field of fetal ultrasound imaging. In multiplanar imaging of the brain structure, it is possible to demonstrate not only the sagittal and coronal sections but also the axial section of the brain, which cannot be demonstrated from parietal direction by a conventional 2D transvaginal sonography. Parallel slicing provides a tomographic visualization of internal morphology similar to MR imaging. Fetal neuroimaging with advanced 3D ultrasound technology is easy, noninvasive and reproducible methods. It produces not only comprehensible images but also objective imaging data. It has been controversial whether ultrasound or MRI is more practical and effective in prenatal assessment of fetal CNS abnormalities.

In the assessment of enlarged ventricles, no significant difference between dedicated neurosonography and MRI in detection of intracranial structure. However, MRI is superior to ultrasound in evaluation of the brainstem, posterior fossa and cortical development especially in the late pregnancy. Meanwhile, transvaginal high-frequent 3D ultrasound has superiority to MRI in detection of intracranial calcification, vascular anatomy, intratumoral vascularity, bony structure.

For CNS anomaly screening scan, ultrasound is no doubt the first modality, and once CNS abnormality is suspicious, after considering each advantage and disadvantage of transvaginal 3D ultrasound and MRI, it is suggested to use those different technologies according to what to be detected and evaluated in each abnormal CNS case. Of course, those two technologies should be utilized as alternatives and complementaries as well. In terms of fetal neurological function analysis, four-dimensional ultrasound research on fetal behavior have been launched in multicenters, and it will be greatly expected to elucidate relations between antenatal behavior and postnatal neurological prognosis.

Screening of the congenital heart disease (CHD) is one of the most important techniques in prenatal ultrasonographic examination. Step by step screening methods for taking account for the level of screener, especially in the area with poor detection rate, is needed for starting effective fetal CHD screening. In this review, the fetal cardiac screening is divided into two methods accounting for steps for learning screening technique; the basic screening and the advanced screening. Basic screening is a simple method even for the one who is not familiar to the cardiac anatomy. The goal of this basic screening is to detect most of the ductal dependent lesions including transposition of the great arteries. For the basic screening, ‘location’ and ‘size’ of the heart and vessels are checked in standard fourchamber view and three-vessel view. Advanced screening is a screening for detecting all fetal CHDs, including total anomalous pulmonary venous return. For the advanced screening, the side of the heart is defined, and then the ‘detail anatomy’ and the ‘function and blood flow’ are assessed in all standard screening views, including one fetal abdominal transverse view and three fetal chest transverse views, such as four-chamber, three-vessel and three-vessel and trachea view.

Ultrasonic screening was studied in the congenital and acquired disorders of fetal thorax cavity, diaphragm, lung and heart; those of fetal peritoneal cavity, liver, alimentary tract, abdominal wall; those of fetal kidneys, ureter and urinary bladder; and those of fetal genital organs.

The prenatal diagnosis of fetal bone and small parts is a challenging task to the variable disorders and large number of possible diagnosis. Fetal limb anomalies may be congenital or acquired in utero. The former occur as anomalies either systemically or, in some limbs, due to hereditary or sporadic impairment in the formation or development of bone, cartilage or soft tissue. Acquired anomalies are caused by mechanical factor of an amniotic band or oligohydramnios. Both types present functional and cosmetic abnormalities, and skeletal dysplasia in particular includes lethal diseases, which makes prenatal diagnosis in such cases highly important, both medically and societally. Diagnostic imaging for prenatal diagnosis is accomplished by ultrasound, MRI and CT scan, and chromosomal and genetic diagnosis is also performed as needed. We focus on skeletal dysplasia to review prenatal diagnosis of fetal bone and small part anomalies by noninvasive ultrasound. For the authors as perinatologists, this is the imaging modality of choice.

Ultrasound diagnosis of the preterm birth was discussed in the measurement of uterine cervical length, its significance for the prediction of preterm birth, fetal growth estimation for the study on fetal maturity and fetal lung immaturity assessment with noninvasive ultrasonic techniques for the prediction and treatment of neonatal respiratory distress syndrome.

Multiple pregnancies have a higher risk of both maternal and fetal prognosis. Accurate diagnosis of chorionicity and amnionicity plays an important role for optical perinatal management. In monochorionic pregnancies, there may be several unique pathological complications derived from vascular anastomoses on monochorionic placentation. Twin-twin transfusion, twin-reversed arterial perfusion sequence and single fetal demise have several issues on both perinatal prognosis and management. Recent investments of medical instruments have allowed intervention during prenatal period, such as fetoscopic laser photocoagulation of communicating vessels. These interventions provide more favorable perinatal prognosis. Another risk in multiple pregnancies is congenital anomaly, which is apparently higher than in singleton pregnancy. Therefore, detailed ultrasound examination is necessary for optical management.

Detail evaluation of amniotic fluid, umbilical cord and placenta has been obtained by means of ultrasound new technology, including 3D color Doppler imaging. This paper summarizes fetal membrane anatomy and disorders using many ultrasound images taken by not only 2D gray scale ultrasound but also 3D color Doppler images.

G-band and rapid FISH/QF-PCR are regarded as the gold standards for prenatal chromosomal diagnosis. Numerous microdeletion/ microduplication syndromes, however, are not detectable by conventional karyotyping. So far, we had a dilemma between fetal developmental/structural abnormalities with strong suspicion of chromosomal abnormalities and normal karyotype results. Fetal DNA chip includes more than 6,450 genetic loci and covers more than 100 common genetic diseases with numeric, structural chromosomal anomalies.

In April 2009, we launched prenatal diagnosis by fetal DNA chip of amniotic fluid samples or chorionic villi samples in the selected fetuses with sonographic abnormalities and suspicion of familial genetic disorders. We had seven cases with both abnormal ultrasound findings and pathologic copy number variations by DNA chip. In all cases, normal karyotype was confirmed by G-banding analysis.

Fetal DNA chip (array CGH) may become a strong modality to solve some part of this dilemma. Although we have to be prudent to select the patients, deal with DNA chip results and parental counseling, “sonogenetics” is one of the breakthroughs in prenatal diagnosis, and the further accumulation of case studies will be required in this new field.