At the 11th National Congress of Obstetrics and Gynecology of the Chinese Medical Association held in Xiamen, China, March 12-15, 2015, Prof. Wu Qingqing, Department of Ultrasound Medicine, Beijing Maternity Hospital, Capital Medical University, gave a detailed presentation on the purpose of fetal ultrasound screening at 11-14 weeks of gestation and its importance in clinical practice, respectively. At the same time clinicians brought new thinking about the challenges faced by fetal screening and the application of multidisciplinary combination.
Ultrasonography of the fetus at 11-14 weeks of gestation is becoming increasingly important, and its screening is clinically significant for the following reasons.
In 1992 Nicolaides et al. found that most chromosomally abnormal fetuses showed NT thickening during 11-14 weeks. A prospective study of more than 200,000 pregnant women showed that NT screened more than 75% of fetuses with trisomy 21 and other severe chromosomal abnormalities. Since then, ultrasound screening of fetuses at 11-14 weeks has been introduced nationally and internationally.
How to screen, to what extent and what are the clinical implications? The following is a detailed introduction.
I. Screening for soft markers associated with fetal chromosomal abnormalities (genetic ultrasonography)
Fetal nuchal translucency thickness (NT).
Defined as the thickness of fluid accumulation in the subcutaneous tissue at the back of the fetal neck. The ultrasound image is an echo within the subcutaneous tissue at the back of the neck. First of all the head-rump length measurement requires very strict and there are many conditions to measure the standard and thus check the gestational week. The NT measurement technique also has these criteria: fetal head-rump length 45-84mm; fetal median sagittal plane with natural curvature; image is zoomed to the maximum, showing only the fetal head and upper chest; slight movement of the measurement scale changes the result by only 0.1mm; the widest distance between the skin and the soft tissue of the cervical spine is measured; three measurements are taken and the maximum value is taken. If the measurement is not accurate, a false positive will occur.
Clinical significance of NT measurement results: the 95th percentile of NT is 2.5mm, the possibility of fetal abnormalities occurring greater than or equal to 3mm increases; NT thickening is combined with fetal chromosomal abnormalities in about 10%, most commonly trisomy 21; the thicker the NT, the higher the risk of chromosomal abnormalities; it is closely related to fetal malformations and adverse pregnancy outcomes, especially the risk of precordial disease is 6 times higher than that of children with normal NT.
In addition to NT, abnormal fetal neck ultrasound signs, such as cysts in the neck and edema throughout the fetus, can be seen and are associated with chromosomal abnormalities. Therefore, karyotype analysis is recommended for fetal NT thickening, cysts, and edema. Those with normal karyotype have a 13% increased risk of structural abnormalities later in fetal development, associated with skeletal and cardiac malformations.
Normal NT is less than 5 mm at 14-18 weeks and less than 6 mm at 19-24 weeks.
Fetal nasal bone
The fetal nasal bone is clearly visible during fetal life and the skin of the nasal tip can also be seen, with different measurements from 12-40 weeks of gestation. Absence or shortening of the fetal nasal bone is closely associated with chromosomal abnormalities. Studies have shown that in normal fetuses, at least one side of the nasal bone can be shown, and in fetuses with chromosomal abnormalities, the rate of nasal bone display is significantly decreased. In the absence or hypoplastic nasal bone on both sides, trisomy 13 reached 80% and trisomy 18 reached 62.5%. Therefore, the fetal nasal bone can be used as a screening indicator for fetal chromosomal abnormalities.
The nasal bone is sometimes poorly displayed. With the development of new ultrasound techniques over the years, the posterior nasal triangle can be evaluated very easily.
Choroid plexus cysts
They can be detected in 1-2% of normal fetuses, and in more than 90% of detected normal fetuses they disappear after 26 weeks and are not clinically significant. Chromosomally normal fetuses with choroid plexus cysts are not associated with other anomalies and postnatal development. The incidence of chromosomal abnormalities is 1% for choroid plexus cysts alone and 10% for trisomy 18. In combination with other systemic anomalies, the incidence of chromosomal abnormalities can be up to 46%.
Echo enhancement of the fetal intestinal canal
Trisomy 21 is associated with 4.8% of cases. The rate of occurrence in normal fetuses is 0.6%. In addition to this intestinal canal echo is also associated with fetal cystic fibrosis, intrauterine infection, and amniotic hemorrhage.
Fetal venous duct (DV), umbilical vein: abnormal blood flow and chromosomal abnormalities
The role of the DV is to pump oxygenated blood from the umbilical vein into the fetal heart to supply the vital organs of the heart and brain. Its abnormal blood flow is associated with chromosomal abnormalities, especially the inversion of the diastolic A wave. It is also a marker of genetics as it accounts for 3.2% of whole ploidy, 66.4% of trisomy 21, 58.3% of trisomy 18, 75% of Turner syndrome and 80% of trisomy 21 in more than 10,000 fetuses examined with abnormal DV flow. In addition, umbilical veins do not pulsate under normal conditions, whereas in trisomy 18 and 13, they have pulsatile flow in 90% of cases. So they can also be used as an early predictor of chromosomal abnormalities.
Venous ductus (DV) is also associated with fetal structural abnormalities because it reflects the fetal right heart load, and if the right heart load is increased, such as pulmonary stenosis, there will also be a reversal of the A wave, so it is also a useful indicator.
II. Screening for fetal structural malformations at 11-14 weeks of gestation
The International Society for Ultrasound in Obstetrics and Gynecology issued a screening guideline at the end of 2013 with the aim of advancing the time of screening for fetal anomalies, screening early for soft markers of fetal chromosomal abnormalities, and providing an opportunity for earlier termination of pregnancy in pregnant women with lethal fetal anomalies.
Screening for fetal neurological abnormalities at 11-14 weeks
The general structure of the fetal nervous system is fully developed at 11-14 weeks, but the cerebellar earth and corpus callosum are fully developed at 19-20 weeks of gestation, and the cerebral sulcus begins to develop at 23-25 weeks. 11-14 weeks measurement of BPD/TAD can predict open spina bifida. 26 cases of open spina bifida were detected in more than 20,000 fetuses examined, and the diagnostic rate of BPD less than or equal to 5 th% was 46.2%, and the diagnostic rate of BPD/TAD less than or equal to 1 was 46.2%. The diagnostic rate of BPD less than or equal to 1 is 69.2%, and the combined index has a diagnostic rate of 76.9%, which can be combined with Down screening.
Another indicator associated with neural tube abnormalities is intracranial hyaline thickness (IT). In 199 NT scans, IT was not seen in 49 cases, open spina bifida was suspected in 6 cases, and eventually there were 4 cases of open spina bifida after birth, which can also be used as an indicator for early screening.
The width of the medullary pool of the cerebellum at 11-13 weeks and the posterior cranial fossa is suspected to be enlarged and Blake’s cyst if it is greater than 2.3 mm. If the medullary pool of the cerebellum is particularly small, less than 1.1 mm, open spina bifida can be diagnosed.
Fetal heart abnormalities at 11-14 weeks
NT is associated with fetal heart. 537 cases of precocious heart disease (CHDs) were found in more than 200,000 chromosomally normal fetuses. an NT greater than the 99th percentile increases the risk of CHDs more than 20-fold; an NT greater than the 95th percentile increases the incidence of CHDs by 1:48; an NT greater than the 99th percentile increases the incidence of CHDs by 1:19. the thicker the NT, the higher the incidence of cardiac anomalies. Cervical hydatid tumors are associated with the heart, but their size is not related to the rate of cardiac malformations.
At 11-14 weeks of fetal life the fetal heart is too small to be seen at all, but the fetal heart axis can be seen, and the heart axis is associated with precordial disease. Cardiac axis abnormalities and increased risk of cardiac malformations, especially outflow tract abnormalities, can be associated with chromosomal abnormalities. It is associated with diaphragmatic hernia and thoracic occupations, such as pneumocystic adenoma. Leftward shift of the heart may be associated with abdominal cleft and umbilical bulge. The normal cardiac axis is about 50 degrees early on, with increasing degrees suggesting fa IV, pulmonary atresia, atrial septal defect, and aortic constriction.
Fetal abdominal abnormalities at 11-14 weeks
In the early period, the main focus is on screening for skin abnormalities of the anterior abdominal wall, such as umbilical bulge, ventral fissure, cloacal and bladder exstrophy, and body tissues abnormalities. In 14 cases of abdominal cysts studied in early fetal period, there were 4 cases combined with other systemic anomalies and 10 cases of simple cysts. 10 cases persisted in 2 cases and disappeared in 8 cases during follow-up, all these 8 cases ended with normal fetuses, and one of the 2 cases that persisted was a common bile duct cyst. Therefore, 80% of simple abdominal cysts in fetal life can be absorbed, but differential diagnosis of gastrointestinal and genitourinary tract cysts is necessary.
An enlarged fetal bladder can be a normal variant or combined with chromosomal abnormalities or structural abnormalities. Bladder size correlates with gestational weeks, with bladder length less than 7 mm at 11-14 weeks. giant bladder can occur at any gestational week, greater than 7 mm by 14 weeks, mild enlargement at grade I is 8-11 mm, moderate enlargement at grade II is 12-15 mm, and severe enlargement at grade III is greater than 15 mm.
Fetal skeletal system at 11-14 weeks
The fetal skeletal system is particularly easy to see in the early stages because of the fetal posture and the relatively large fetal space. 40 cases of fetal ultrasound diagnosed limb anomalies such as hand entropion, abnormal ossification, polydactyly, trisomy 18, mermaid sequence syndrome, and osteogenesis imperfecta.
11-14 weeks fetal anomalous syndromes, sequential signs and syndromes
Combined anomalies such as umbilical bulge, bladder exstrophy, anal atresia, spinal defects, early pregnancy OEIS ultrasound features NT thickening, anterior abdominal wall cystic mass, spinal anomalies, and single umbilical artery. As in Cantrell’s pentad, umbilical bulge, cardiac ectasia, sternal cleft sternal segment defect, anterior diaphragmatic wall defect, and pericardial wall defect with abdominal traffic. Combined twins are more meaningful when detected early, allowing for early termination of the pregnancy, and delivery is difficult when detected in the mid to late stages.
Another indicator at 11-14 weeks is the uterine artery blood flow. 11-14 weeks bilateral uterine arteries at normal is 34.2% presence of diastolic early cut-off. The presence of the tangent is associated with its resistance index and with the occurrence of a baby younger than gestational age.