Classification and indications
Ultrasound anatomical examination of the fetus in early pregnancy can be divided into three categories: basic (class I), detailed (class II), and targeted (class III) examinations. In cases where clinicians are not satisfied with transabdominal ultrasound examination, a transvaginal ultrasound examination can be performed if there are no contraindications for transvaginal ultrasound examination and the pregnant woman agrees to it after being informed of the procedure.
Basic ultrasound anatomical examination of the fetus in early pregnancy (class I)
This technique is suitable for screening low-risk fetuses and is primarily used to detect any ultrasound anatomical abnormalities in the fetus in early pregnancy. Hospitals with the necessary resources may choose to perform a more detailed examination.
Detailed ultrasound anatomical examination of the fetus in early pregnancy (class II)
Fetal anatomical ultrasound examinations in early pregnancy include one measurement project (with 6 sub-projects) and 10 examination projects (with 26 sub-projects), which contain both recommended and suggested contents. All recommended contents are included in the basic ultrasound anatomical examination of the fetus in early pregnancy, while the detailed ultrasound anatomical examination includes both the recommended and suggested contents.
Generally, if no fetal abnormalities are observed following basic or detailed ultrasound anatomical examination of the fetus in early pregnancy, there is no need to perform targeted examination.
Targeted ultrasound anatomical examination of the fetus in early pregnancy (class III)
Targeted ultrasound anatomical examination of the fetus in early pregnancy is a type of examination driven by indications, and is generally recommended to be performed between 13+ 0 to 13+ 6 weeks of gestation. Targeted ultrasound examination includes both recommended and suggested contents. The recommended items are necessary for the examination, while the suggested items are not necessary and can be ignored if the image is difficult to display owing to the examination conditions. Indications for targeted fetal ultrasound anatomical examination include the following [10, 11]: (1) definite or suspected fetal abnormalities detected by ultrasound or clinically in the current pregnancy, such as increased nuchal translucency thickness, fetal structural abnormalities that are visible or suspected based on ultrasound and clinical examinations, high-risk results of prenatal screening tests (such as the triple or quadruple test or non-invasive prenatal testing), and abnormal results on chorionic villus sampling or non-invasive DNA testing; (2) a history of previous adverse pregnancy outcomes, such as fetal malformations or genetic or chromosomal abnormalities; (3) maternal factors that increase the risk of fetal malformations, such as (i) maternal age of 35 years or more, (ii) pre-existing metabolic disorders such as diabetes, phenylketonuria, or autoimmune diseases, (iii) a personal or family history of congenital malformations, such as cleft lip and palate or congenital heart disease, (iv) chemical exposure to teratogenic drugs or physical exposure to radioactive substances, (v) viral infections, (vi) conception through assisted reproduction, or (vii) multiple pregnancies; and (4) other situations that may require targeted fetal ultrasound anatomical examination in clinical settings.
Institutions and applications
Basic examination is applicable to county-level central hospitals and maternal and child health hospitals with screening/diagnostic qualifications. Detailed examination is applicable to comprehensive hospitals and maternal and child health hospitals at the municipal level with screening/diagnostic qualifications. Targeted examination is applicable to prenatal diagnosis centers with diagnostic qualifications.
Management and quality control
Strict quality control and management are key to improving the quality of ultrasound anatomical examination of the fetus in early pregnancy to reduce the rates of misdiagnosis and missed diagnosis for prenatal ultrasound examination in early pregnancy. Certain measures can be taken to ensure quality control. These include collecting and saving images of relevant standard sections according to different categories of ultrasound examination projects and corresponding examination contents, conducting prenatal ultrasound examinations from 11+ 0 to 13+ 6 weeks of gestation, and standardizing the writing of ultrasound reports (Appendix 1).
If satisfactory ultrasound images cannot be obtained owing to fetal position or maternal obesity, and a detailed examination is required, it is recommended to change the position or have the patient move and then perform a re-examination. If necessary, a higher-level doctor may be consulted. If the image is still unsatisfactory, it should be noted in the ultrasound report, and a short-term follow-up examination is recommended.
Regarding multidisciplinary consultation, if fetal abnormalities are suspected during early pregnancy ultrasound examination, referral to a prenatal diagnosis center with diagnostic qualifications for consultation is recommended, and multidisciplinary consultation may be necessary. It is recommended that pregnant women or her authorized dependents participate in these multidisciplinary consultations involving ultrasound doctors, obstetricians, pediatricians, geneticists, and radiologists to facilitate comprehensive evaluation and provide relevant opinions and suggestions.
A four-step management strategy should be established involving a system for prenatal ultrasound and clinical follow-up tracking in early, mid, and late pregnancy and after delivery. For diagnoses that cannot be made in early pregnancy, follow-up re-examination is recommended in mid-pregnancy.
Basic and detailed ultrasound anatomical examinations of the fetus at 11+ 0 to 13+ 6 weeks gestation
Basic and detailed ultrasound anatomical examinations should be applied to low-risk fetuses for early pregnancy ultrasound screening and must be performed by qualified institutions and personnel. The examination sections (Fig. 1) and contents used in the present study are shown in Table 1. For multiple pregnancies, the number of chorionic membranes and amniotic sacs should be noted, while for monochorionic multiple pregnancies, images of the placental cord insertion site should also be obtained. Cases of concomitant uterine adnexal diseases, such as uterine fibroids (especially fibroids at the site of placental attachment) and ovarian cysts, should also be noted [10].
Table 1
Basic and detailed ultrasound examinations of the fetal anatomy at 11+ 0 to 13+ 6 gestational weeks
Organ | Structure /measure | R/ S | Suggested plane | Key features | Possible anomalies |
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Measure | Crown-rump length | R | | | |
Nuchal translucency | R | | | |
Biparietal diameter | S | | | |
Head circumference | S | | | |
Abdominal circumference | S | | | |
Femoral diaphysis length | S | | | |
Head and brain | Skull | R | Ax | Oval uninterrupted shape, uniformly hyperechoic | Anencephaly, encephalocele, exencephaly |
Midline falx | R | Ax | Uninterrupted | Holoprosencephaly |
Lateral ventricles/CP | R | Ax | Symmetric, fulfilled by CP | Ventriculomegaly |
Cranial posterior fossa | R | Sag | Three similar anechoic spaces | Chiari malformation, cystic anomalies |
Neck | Nuchal translucency | R | Sag | Thickness < 95th centile | Marker for anomalies |
Spine | Vertebrae | R | Sag, Co | Uninterrupted vertebral line | Open spina bifida, kyphoscoliosis, scoliosis |
Dorsal skin | R | Sag | Uninterrupted skin | Myelomeningocele |
Face | Profile | R | Sag | No flat, no abnormal protrusions, regular chin, nasal bone | Micrognathia, flat face, Nasal bone loss |
Orbits | R | Sag, Co | Symmetrical anechoic orbit, lens, and ears | Microphthalmia, hypertelorism, cataracts, absence of ears |
| Anterior palate | S | Co, Ax, Sag | Uninterrupted bone, superposition line feature | Cleft palate |
Thorax | Lung fields | R | Ax, Sag | Homogeneous structure, shape continuity with abdomen | Pleural effusion, diaphragmatic hernia, lung agenesis, CHAOS, severe skeletal dysplasia |
Heart | Heart activity | R | Ax | Regular, 150–180 bpm | Arrhythmias |
Cardiac situs | R | Ax | Located in the left chest cavity, with the heart axis to the left(30°–60°) | Isomerism |
Size | R | Ax | Cardiothoracic area ratio of about 1/4 to 1/3 | Diaphragmatic hernia, hypoplastic Rt/Lt heart, ectopia cordis, heart failure, cardiomyopathy |
Four chambers | R | Ax | Four balanced chambers (consider Doppler) | Single chamber heart, hypoplastic Rt/Lt heart, valvular stenosis/ atresia, AV septal defect |
Three vessels/ arches | S | Ax | V-sign, balanced arches, Doppler suggested | Cono-truncal anomalies, valvular stenosis/ atresia |
GIT and abdominal wall | Stomach | R | Ax | anechoic, left-sided Morphological variability | Diaphragmatic hernia, esophageal or duodenal atresia |
Cord insertion | R | Ax, Sag | No bowel protrusion | Exomphalos, gastroschisis, body stalk anomaly |
Abdominal and venous catheter blood flow spectrum | R | Ax, Sag | Continuous diaphragm, three-phase waveform of venous catheter | Abnormal flow spectrum, diaphragmatic hernia |
Urinary tract and genitalia | Bladder | R | Ax, Sag | Round-shaped, anechoic, diameter < 7 mm | Bladder exstrophy, bilateral renal agenesis, megacystis, LUTO, cloacal anomaly |
Umbilical arteries | R | Ax | Two arteries on the bladder sides (Doppler) | Single umbilical artery |
Kidneys | S | Ax, Co | Two symmetric kidneys, homogeneous structure, upper abdomen | Renal agenesis, pelvic/horseshoe kidney, cystic/hyperechoic kidneys, hydronephrosis |
Genital tubercle | S | Sag | Flat shape for females, upward position for males | - |
Limbs | Active movements | R | - | Flexion/extension | Neuromuscular anomalies, FADS |
Three segments | R | Ax, Sag | Bones present, regular proportions | Limb reduction defects, skeletal dysplasia |
Hands/feet | R | Ax, Sag | Present | Limb reduction defects |
The basic examination included all recommended items, whereas the detailed examination included the recommended and suggested items |
Ax, axial; AV, atrioventricular; bpm, beats per minute; CHAOS, congenital high airways obstruction syndrome; Co, coronal; CP, choroid plexus; FADS, fetal akinesia deformation sequence; GIT, gastrointestinal tract; Lt, left; LUTO, lower urinary tract obstruction; R, recommended; Rt, right; S, suggested; Sag, sagittal |
Targeted ultrasound anatomical examination of the fetus at 11+ 0 to 13+ 6 weeks gestation
Targeted fetal ultrasound anatomical examination is performed only under the indicated conditions. Currently, three sites or organs are performed for targeted ultrasound examinations.
Targeted examination of the central nervous system of the fetus at 11 + 0 to 13+ 6 weeks gestation
The main sections (Fig. 2) and contents of the targeted examination of the fetus's central nervous system are shown in Table 2. Three-dimensional ultrasound technology can be used to improve the display effect of the fetal central nervous system. Through targeted examination of the fetus’ central nervous system, abnormalities such as holoprosencephaly, lateral ventricular dilation, open spina bifida, Dandy-Walker malformation, and agenesis of the corpus callosum can be detected early [12–14].
Table 2
Targeted ultrasound examination of the central nervous system of fetuses at 11+ 0 to 13+ 6 gestational weeks
Suggested plane | R/S | Structure | Key features | Possible anomalies |
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Suprathalamic axial view | R | Skull | Complete strong echo ring | Anencephaly, exencephaly, encephalocele |
Brain middle | Straight and continuous high echo lines | Holoprosencephaly |
Lateral ventricles and choroid plexus | The choroid plexus occupies almost the entire lateral ventricle in a "butterfly" shape | Ventricular dilatation, hydrocephalus, choroid plexus cyst |
Archicortex | The choroid plexus occupies almost the entire lateral ventricle, forming echoic tissue inside the "butterfly" shaped skull. There are no brain sulci or gyri, but the precursor of the lateral fissure can be observed | Schizencephaly |
Transsection of thalamus | R | Brain middle | Only the first 1/3 is displayed | Malformation of the brain line structure |
Thalamus | Bilateral symmetrical oval hypoecho | Whole forebrain without lobes |
Third ventricle | The bilateral thalamus is slender and anechoic | Hydrocephalus |
Aqueduct of Sylvius | There is no echo in the posterior rectangle of the thalamus | Mesencephaly |
Mesencephalic tectum (tetraplegia) | Medium-high echo on both sides of the aqueduct | |
Anteroposterior median sagittal profile | R | Diencephalon | Round, medium echo | |
Brainstem | "S" shaped medium echo, including the midbrain, pons, medulla oblongata | |
Fourth ventricle | No echo in the back of the brain stem | |
Cisterna fossa posterior | No echo behind the fourth ventricle | |
Brain-stem-occipital spacing | The ratio ranges from 0.5 to 1.0 | Open spina bifida, Chiari-II deformity, Dandy-Walker deformity |
The dome joins with the front | Hyperechoic thin band above the anterior diencephalon | |
Median sagittal profile posteriorly forward | S | Midbrain aqueduct and fourth ventricle | There is no echo behind the brain stem, which is separated by an isthmus | Posterior encephaly |
Aqueduct of Sylvius | The medial tectum forms the apex | |
Top of the fourth ventricle | The choroid plexus is divided into the upper and lower medulla, namely the anterior and posterior membranes. The anterior membranes continues with the vermis of the cerebellum and gradually disappears with the development of the vermis of the cerebellum. The posterior membranes show a "finger-like" projection toward the cistern of the posterior fossa to form the Blake lacuna | Cyst of Blake lacunae |
Coronal section of transfrontal lobe | R | Brain middle | Continuity and symmetry | Holoprosencephaly without lobes |
Lateral ventricles and choroid plexus | The choroid plexus fills the lateral ventricles | |
Frontal bone | | |
Eye orbit and lens | Anechoic eyeball and strong oblate echo | Malformation of the eyeball and lens |
Coronal cross-section via the caudate nucleus | S | Brain middle | Continuity and symmetry | Abnormal brain parenchyma and intracranial structure |
Choroid plexus | Hyperechoic and filled the lateral ventricles | |
Basal ganglion | Hypoechoic | |
Basal nuclei | Hypoechoic | |
Third ventricle | Non-expansion | |
Transthalamic coronal view | S | Brain middle | Continuity and symmetry | Abnormal brain parenchyma and intracranial structure |
Lateral ventricles and choroid plexus | The choroid plexus fills the lateral ventricles | |
Thalamus | Hypoechoic and bilateral symmetrical | |
Third ventricle | Echoless, no expansion | |
Coronal view of the brain stem via the occipital lobe | S | Paracele | symmetry | Abnormal brain parenchyma and brain stem structure |
Aqueduct of Sylvius | Located between the tectal cortex of the midbrain | |
Tectum mesencephali | Medium-high echo and symmetrical | |
Cerebellar hemispherical precursor | Located on both sides of the brain stem | |
brainstem | Medium echo and centered | |
Coronal cross-section of the fourth ventricle via the occipital lobe | S | Paracele | Symmetry | Abnormal brain parenchyma and posterior brain structure and brain stem |
Aqueduct of Sylvius | The absence of echo is located between the midbrain tectum | |
Tectum mesencephali | Medium-high echo, bilateral symmetry | |
Isthmus | Closely related to the aqueduct | |
Cerebellar hemispherical precursor | Isoecho, bilateral symmetry | |
Fourth ventricle and choroid plexus | Centered, echoless, choroid plexus hyperechoic | |
Brainstem | Located at the foot of the fourth ventricle, the echo was moderate | |
Median sagittal profile of intracranial vessels | S | Pericallosal artery and its branches | Located above the corpus callosum and gives off tree-like branches | Agenesis corporis callosi |
Internal carotid | | |
Vertebrobasilar artery | | |
Confluence of sinus | The inferior, superior sagittal sinus and Galen vein flow into the straight sinus, and all three flow into the sinuses | Venous lesions or thrombosis |
Axial view of intracranial blood vessels | S | Cerebral arterial circle | The anterior cerebral artery, the middle cerebral artery, the posterior cerebral artery, and the posterior communicating artery form a "benzene ring" like color blood flow | Malformation of the cerebral artery |
The suggested items are non-essential and can be ignored if the affected ultrasound examination is not satisfactory. R, recommended; S, suggested |
Targeted ultrasound anatomical examination of the fetal heart at 11+ 0 to 13+ 6 weeks gestation
The main sections (Fig. 3) and contents of the targeted ultrasound examination of the fetal heart are shown in Table 3. Color Doppler flow imaging technology should be used to enhance the display effect of the fetal heart structure. Most major cardiac abnormalities can be detected early with targeted ultrasound examination of the fetal heart [15–18].
Table 3
Targeted ultrasound examination of the fetal heart at 11+ 0 to 13+ 6 gestational weeks
Suggested plane | R/S | Structure | Key feature | Possible anomalies |
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Transverse view of abdomen | R | Magenblase | On the left and not echoic | Diaphragmatic hernia, esophageal or duodenal atresia, visceral ectopic |
Cross section of the aorta and inferior vena cava | The aorta is located on the left front of the spine, and the inferior vena cava is located on the right front of the aorta | Visceral ectopic, cardiac translocation/ectopic, complex congenital heart disease |
Umbilical veins Venous catheter and spectrum | The sagittal sinus of the portal vein bends to the right. Maximum ventricular systolic flow rate (S wave), maximum ventricular diastolic flow rate (D wave), and forward atrial systolic flow rate (a wave) | Permanent right umbilical vein, atrial isomerism Venous catheter absent, wave a reversed or disappeared |
Four-chamber view | R | Location | Located in the left thoracic cavity, the mandrel to the left (30°–60°) | Lung disease, diaphragmatic hernia, heart transposition/ectopic, complex congenital heart disease |
Size | The cardiothoracic area ratio is approximately 1/4–1/3 | Heart failure, complex congenital heart disease |
Four chambers and two sets of atrioventricular valves | The left and right atria and ventricles are largely symmetrical, forming a "cross." CDFI showed the two bundles of blood flow were basically symmetrical, without tricuspid regurgitation | Complex congenital heart disease |
View of left ventricular/right ventricular outflow tract | R | Left ventricular outflow tract and right ventricular outflow tract | The aorta originates from the left ventricle, and the pulmonary artery from the right ventricle. Crosses showing valves are included. The CDFI blood flow is separated, laminar, and symmetrical | Malformations of the great arteries, obstruction or atresia of the outflow tract, abnormal valves |
Tri-vessel/tri-vessel - trachea view | R | Pulmonary artery | Located on the left side of the aorta with an internal diameter larger than that of the aorta. It has backward-flowing blood flow, and the borrowing catheter joins the aorta into the descending aorta | Malformation of the conical trunk of the great artery, ectopic pulmonary vein drainage, branch vagus/ectopic of the great artery |
Aorta | Located on the right side of the pulmonary artery and the left side of the trachea, with an inner diameter smaller than the pulmonary artery. It flows backward and into the descending aorta with the arterial catheter |
Precava | Located on the right side of the aortic arch, the inner diameter is smaller than the aorta |
Airtube | Located behind the right arch of the aorta, no blood vessels passing behind |
Bilateral subclavian artery view | S | | The blood vessels emanate from the aortic arch, and the CDFI blood flow is "W" shaped and symmetrical bilaterally | Subclavian artery vagus |
The suggested items are non-essential and can be ignored if the affected ultrasound examination is not satisfactory. R, recommended; S, suggested |
Targeted ultrasound examination of cleft lip and palate of the fetus at 11 + 0 to 13+ 6 weeks gestation
The main sections (Fig. 4) and contents of the targeted ultrasound examination of the cleft lip and palate of the fetus are shown in Table 4. Targeted ultrasound anatomical examination of the cleft lip and palate of the fetus can early detection of cases of primary and secondary cleft palate [19–21].
Table 4
Targeted ultrasound examination of fetal cleft lip and palate at 11 + 0 to 13 + 6 gestational weeks
Suggested plane | R/S | Key features | Possible anomalies |
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Transverse section of the maxillary alveolar process | R | Continuous integrity of the maxillary alveolar process | Alveolar process cleft, cleft lip and palate |
Median sagittal section | R | Continuous integrity of the palatal line, no "overlapping line" sign, and no sign of a maxillary bone gap. | Cleft lip and palate, isolated cleft palate, isolated cleft palate with micrognathia |
Oblique coronal section of the posterior nasal triangle | R | Continuous integrity of the posterior nasal triangle base, mandibular gap. | Primary cleft palate, micrognathia or severe retrognathia |
Coronal section of the nose and lips | S | Continuous integrity of the lip | Cleft lip |
Transverse section of the horizontal plate of the palate | S | Horizontal plate of the palate, maxilla, and tongue. | Secondary cleft palate |
The suggested items are non-essential and can be ignored if the affected ultrasound examination is not satisfactory. R, recommended; S, suggested. |