Human fetal foramen ovale flow velocity waveforms relative to fetal breathing movements in normal term pregnancies.

The relationship between foramen ovale flow velocity waveforms and high-amplitude fetal breathing movements was studied in ten normal term pregnancies using Doppler ultrasonography. Peak systolic and averaged flow velocities demonstrated a statistically significant increase during fetal breathing activity, suggesting a raised pressure gradient between the right and left atria. This could be explained by a temporal reduction in pulmonary venous return to the left atrium during the inspiratory phase of the fetal breathing cycle. The breathing-related increase in foramen ovale flow velocity suggests that fetal breathing activity facilitates the distribution of well-oxygenated blood to the aorta and cerebral circulation.     

The fetal thyroid: normal and abnormal sonographic measurements.

The thyroid of 31 fetuses at low risk for perinatal thyroid disease were evaluated sonographically. The transverse width and circumference of the fetal thyroid was measured prospectively to provide normative values for each gestational age. In addition, the thyroid of 23 fetuses at risk for thyroid disease were examined sonographically and compared to the control group. At birth, 18 of the neonates had no evidence of thyroid dysfunction, whereas 5 newborns had goiters and abnormal thyroid function. The fetal thyroid measurements for these 5 neonates were above the upper limit of the 95% confidence interval compared to the control group. The other 18 fetuses in the group at risk for thyroid disease but without evidence of thyroid dysfunction at birth had fetal thyroid measurement within the normal range.     

Fetal gastric size in normal and abnormal pregnancies.

OBJECTIVE: The aim of this observational study was to construct an ultrasound index of fetal gastric size for the prenatal detection of congenital digestive tract obstruction. SUBJECTS: A total of 386 fetal measurements were performed in routine ultrasonographic examinations of women with normal singleton pregnancies between 18 and 39 weeks of gestation. Gastric measurements were also performed in 13 fetuses with digestive tract obstruction. METHODS: The ultrasound plane which included the pylorus and which provided the largest stomach area was used for definition and measurement of gastric area and maximal longitudinal dimension. The transverse section at the center of the gastric corpus was used for transverse and anteroposterior dimensions. Gastric volumes were calculated as a prolate ellipsoid. The gastric area ratio was defined as the gastric area divided by the transverse abdominal area. Biparietal diameter (BPD) and abdominal transverse area were also measured. RESULTS: The fetal gastric area was significantly correlated with fetal gastric volume (r = 0.91) and gestational age (r = 0.74). However, the correlation coefficient for gastric area with gestational age was smaller than those of the BPD (r = 0.97) with gestational age and abdominal transverse area with gestational age (r = 0.97). Gastric area ratio decreased slightly towards term. The gastric area ratio was below the 95% confidence intervals for the predicted values in all five fetuses with esophageal atresia, and exceeded the 95% confidence intervals in seven of the eight fetuses with duodenal atresia or intestinal tract obstruction. CONCLUSION: Fetal gastric area correlates with ultrasound-determined gastric volume measurements and appears to be useful in the assessment of digestive tract anomalies.     

Tomographic ultrasound imaging of the fetal heart: a new technique for identifying normal and abnormal cardiac anatomy.

OBJECTIVE: In 2003 and 2004, the American College of Radiology, the American Institute of Ultrasound in Medicine, and the American College of Obstetricians and Gynecologists published guidelines for the standard ultrasound examination of the fetus. Each group recommended that the outflow tracts of the fetal heart be examined if technically feasible. One method to accomplish this task is to perform a free-hand sweep of the transducer beam directed in a transverse plane from the 4-chamber view to the fetal neck. One problem with this approach is that the examiner may not direct the beam transversely and, therefore, may not accurately identify the outflow tract anatomy. METHODS: A new technology, tomographic ultrasound imaging (TUI), allows the examiner to obtain a volume data set that simultaneously displays multiple images at specific distances from the 4-chamber view. This study examined TUI technology for identifying normal and abnormal fetal cardiac anatomy with the use of either static or spatiotemporal image correlation volume data sets. RESULTS: The 4 views used in the screening examination of the outflow tracts of the fetal heart (4-chamber, 5-chamber, 3-vessel, and tracheal views) could be identified with the use of TUI technology in fetuses between 13 and 40 weeks' gestation. Examples of fetuses with abnormal cardiac anatomy of the outflow tracts (tetralogy of Fallot, transposition of the great vessels, and pulmonary stenosis) all showed abnormal anatomy on TUI. CONCLUSIONS: Tomographic ultrasound imaging technology enables the fetal examiner to evaluate the 4-chamber view and the outflow tracts in a systematic manner to identify normal and abnormal cardiac anatomy.     

Three-dimensional ultrasonography of the fetal distal lower extremity: normal and abnormal.

The objective of this study was to compare two-dimensional and three-dimensional ultrasonographic evaluation of fetal distal lower extremities. Data from two-dimensional and three-dimensional ultrasonographic examinations from 40 distal lower extremities in 33 fetuses from a predominantly high-risk patient population were compared. Three-dimensional ultrasonography routinely provided three orthogonal planes (coronal, sagittal, and axial) for distal lower extremity evaluation. Specific features of distal lower extremity evaluation were not different using two-dimensional and three-dimensional ultrasonography. Rotation of the rendered volume provided assistance in assessing all but one of 40 distal lower extremities. Time from image acquisition to assessment for two views (coronal and sagittal) was longer with three-dimensional ultrasonography (8.2 min) than with two-dimensional ultrasonography (3.2 min). Confidence in the diagnosis of abnormal distal lower extremities was slightly improved using three-dimensional ultrasonography compared to two-dimensional ultrasonography. Pregnancy management was assisted in three of the four cases with isolated limb anomalies. In conclusion, three-dimensional ultrasonography improves the ability to evaluate the fetal distal lower extremity because of the multiplanar nature of volume assessment and the ability to rotate volume data sets. In addition, it provides assistance in counseling families, particularly for cases involving isolated limb anomalies.     

Anatomy and physiology of feeding and swallowing: normal and abnormal

Eating and swallowing are complex behaviors involving volitional and reflexive activities of more than 30 nerves and muscles. They have two crucial biologic features: food passage from the oral cavity to stomach and airway protection. The swallowing process is commonly divided into oral, pharyngeal, and esophageal stages, according to the location of the bolus. The movement of the food in the oral cavity and to the oropharynx differs depending on the type of food (eating solid food versus drinking liquid). Dysphagia can result from a wide variety of functional or structural deficits of the oral cavity, pharynx, larynx, or esophagus. The goal of dysphagia rehabilitation is to identify and treat abnormalities of feeding and swallowing while maintaining safe and efficient alimentation and hydration.     

Time domain measurement of blood flow in the human fetal aorta during normal pregnancy.

OBJECTIVE: To evaluate blood-volume flow-rate measurement in the fetal descending thoracic aorta using a non-invasive, non-Doppler, ultrasound technique. METHODS: This was a cross-sectional, observational study. Volume flow measurements were obtained from the descending thoracic aorta in 59 human fetuses between 20 and 40 weeks' gestation. These were uncomplicated pregnancies that resulted in the live births of appropriately grown infants. The measurements were obtained using a time domain processing technique: color velocity imaging quantification (CVI-Q). RESULTS: The blood-volume flow rate increased consistently from the second trimester until term. The mean values ranged between 100 mL/min at 20 weeks' gestation and approximately 350 mL/min at term. The normalized (weight-adjusted) volume flow rates decreased with increasing gestation, from a maximum of 626 mL/min/kg at 23 weeks to a minimum of 45.6 mL/min/kg at 37 weeks. CONCLUSIONS: The regular measurement of blood-volume flow in the descending fetal thoracic aorta is feasible using CVI-Q. Although there is a considerable learning curve, with adequate training there are potential clinical applications for this non-Doppler technique. However, limitations exist with the currently available technology for clinical use in fetal vascular studies.     

The fetal portal vein: normal blood flow development during the second half of human pregnancy.

OBJECTIVES: The umbilical vein is the major source of blood for the fetal liver, but portal blood, which has not been measured directly in human fetuses, probably constitutes a physiologically important contribution. We aimed to establish a method for measuring blood flow in the fetal portal vein and to produce longitudinal reference ranges for diameter, blood flow velocities and volume blood flow during the second half of pregnancy. METHODS: After a pilot project to develop the measuring technique, 160 low-risk pregnant women were recruited to a longitudinal study that included ultrasound examinations at 4-5-week intervals starting at 20-22 weeks of gestation. The inner diameter (D) of the vessel was measured with a perpendicular insonation angle, and the time-averaged maximum blood velocity (TAMXV) and weighted mean velocity (VWMEAN) were recorded with an insonation directed along the long axis of the vessel. Portal flow was calculated as: Q = pi(D/2)(2) x h x TAMXV (where h is a velocity profile parameter and equals 0.5). Portal flow was normalized for estimated fetal weight based on birth-weight percentiles. RESULTS: The portal vein could be visualized and measured in 558/593 (94%) cases. Blood flow was pulsatile. D and TAMXV doubled during the second half of pregnancy (21-39 weeks), from 1.5 to 3.4 mm and from 8.4 to 14.9 cm/s, respectively. Correspondingly, the portal flow increased from 5 to 41 mL/min, and from 10 to 13 mL/min/kg when normalized for fetal weight. Similar results were achieved for VWMEAN. CONCLUSION: Portal flow can be measured with a standardized technique. It increases during the second half of pregnancy, even when normalized for fetal weight, suggesting that it has increasing importance in the fetal liver circulation.     

Foramen ovale: an ultrasonographic study of its relation to the inferior vena cava, ductus venosus and hepatic veins.

According to the literature, oxygenated blood from the ductus venosus and hepatic veins may either enter the right atrium before flowing through the foramen ovale to the left atrium, or flow directly from the ductus venosus and the hepatic veins to the foramen ovale, bypassing the right atrium. To address this problem, 103 normal fetuses were examined by two-dimensional imaging, M-mode and color Doppler at an average gestational age of 27 weeks (range, 15-40 weeks). The position of the ventricular septum and foramen ovale, and the angle and flow direction of the inferior vena cava, ductus venosus and hepatic veins were recorded. Two pathways for blood were described: a left ductus venosus-foramen ovale pathway that delivers blood directly to the foramen ovale circumventing the right atrium, and a right inferior vena cava-right atrium pathway that delivers blood into the right atrium through the right portion of the proximal inferior vena cava at an angle of 13 degrees to the long axis of the spine. The left and medial hepatic veins enter the left ductus venosus-foramen ovale pathway, and the right hepatic vein enters the right inferior vena cava-right atrium pathway. This supports the hypothesis that oxygenated blood from the ductus venosus and left hepatic veins flows directly through the foramen ovale to the left atrium avoiding extensive mixture in the inferior vena cava and an intermediate entrance to the right atrium.     

MR evaluation of cardiovascular physiology in congenital heart disease: flow and function.

Cardiovascular magnetic resonance (CMR) has become the method of choice in the evaluation of a number of questions in congenital heart disease. In addition to morphology, modern CMR techniques allow the visualization of function and flow in a temporally resolved manner. Among the pathologies where these methods play a major role are shunts, septal defects, aortic coarctation, anomalies of the pulmonary arteries, and valvular regurgitation. This paper explains the basics of functional and flow encoded CMR and discusses their application in the assessment of several types of congenital heart disease.     

Ultrasound assessment of the fetal foramen ovale.

OBJECTIVES: Based on the assumption that the horizontal area between the fetal foramen ovale valve and the atrial septum (the outlet) represents the limiting structure for the foramen ovale flow, our objective was to determine the normal size of this section during the second half of pregnancy. METHODS: One hundred and thirty-eight women with low-risk singleton pregnancies were examined in a cross-sectional study between 18 and 42 weeks of gestation. Using ultrasound imaging and M-mode, the area and diameter between the foramen ovale valve and the atrial septum were determined in a four-chamber view of the fetal heart above the foramen ovale limbus. The inferior vena cava cross section and right atrial width were also determined. RESULTS: The mean foramen ovale width increased from 3 mm at 18 weeks to 6 mm at term. Correspondingly, the horizontal area grew from 15 to 50 mm2. The mean ratio between this area and the area of the inferior vena cava fell from 1 at 18 weeks to 0.5 at term. The ratio between the transverse width of the foramen ovale and the right atrium remained at average 0.45-0.50 until 32 weeks, when a slight reduction was observed towards term. CONCLUSIONS: Normal values for the horizontal cross section and transverse diameter of the foramen ovale outlet were established for the second half of pregnancy. In particular, the horizontal transverse diameter and its ratio to the right atrial width are easy to determine, and use of these measurements is thus suggested for the assessment of the fetal foramen ovale.     

The fetal mandible measurement: an objective determination of fetal jaw size.

The sonographic diagnosis of micrognathia has been limited by the lack of an objective measurement of the fetal mandible. A cross-sectional study of 134 normal patients of known gestational age between 14 and 39 weeks' gestation was performed. Models to predict mandible length based on gestational age, biparietal diameter, head circumference or femur length were derived by least squares regression analysis. The 95% prediction limits were also derived. Utilization of these curves generated from a normal population should allow for a more sensitive and reproducible method to diagnose micrognathia in the fetus.     

Three-dimensional ultrasonography of normal fetal heart: comparison with two-dimensional imaging.

Thirty-one high-risk patients (16 to 35 weeks' gestation) underwent two-dimensional and three-dimensional ultrasonography to compare two-dimensional and non-cardiac-gated three-dimensional ultrasonography of the normal fetal heart. After normal two-dimensional studies, three-dimensional sonographic volumes were acquired without cardiac gating in transverse and longitudinal planes. Standard cardiac views were derived from three-dimensional data, analyzed, and rated as follows: (1) not identifiable, (2) identifiable but inadequate for diagnosis, (3) adequate, and (4) excellent. Two-dimensional ultrasonography demonstrated better yields of diagnostically acceptable images of basic echocardiographic views (four-chamber view, 100% for two-dimensional sonography versus 10 to 71% for three-dimensional sonography; right ventricular outflow tract, 42% for two-dimensional versus 6 to 26% for three-dimensional ultrasonography; left ventricular outflow tract, 71% for two-dimensional versus 13 to 45% for three-dimensional sonography). In one subject three-dimensional ultrasonography was superior to two-dimensional sonography in demonstrating an outflow tract. Aortic and ductal arches were not imaged with the two-dimensional technique but were available from the acquired three-dimensional volumes in 3 to 32% and 23%, respectively. False-positive and false-negative findings were observed on three-dimensional ultrasonograms. Overall, compared to two-dimensional ultrasonography, non-cardiac-gated three-dimensional sonography yielded inadequate reconstructed image quality of basic echocardiographic views (four-chamber view, right ventricular outflow tract, left ventricular outflow tract). Three-dimensional ultrasonography, however, shows potential for allowing nonechocardiographers to acquire some diagnostically acceptable views of the aortic and ductal arches.     

The physiology of fetal heart rate patterns and perinatal asphyxia

The purpose of electronic fetal heart rate (FHR) monitoring is the ongoing assessment of fetal oxygenation. FHR tracings are analyzed for characteristic patterns that signify specific hypoxic or nonhypoxic events. A working knowledge of fetal physiology and the fetal response to hypoxia can aid and refine clinical interpretation of FHR patterns during labor. This article reviews the fetal response to decreased oxygenation, the physiology of subsequent FHR patterns and the clinical presentation of asphyxia in the newborn.     

胎儿期动脉导管血流异常对先天性右心系统畸形患儿预后的评估价值

目的:探讨胎儿期动脉导管内血流变化对先天性右心系统畸形患儿出生后预后的预测和评价作用。方法:2015年2月至2017年2月产前诊断为先天性右心系统畸形的胎儿68例,依据胎儿期动脉导管血流变化,将其分为3组:A组(动脉导管内正向血流)、B组(动脉导管内双向血流)和C组(动脉导管内逆向血流)。随访至出生后6个月,分析各组患儿预后与其胎儿期动脉导管内血流方向变化的关系。结果:68例右心系统畸形胎儿中,A组31例(45.6%),B组25例(36.8%),C组12例(17.6%)。随着动脉导管内逆向血流的增多,肺动脉狭窄和肺动脉闭锁所占比例逐渐增高,且伴发右心室发育不良。39例随访至出生后6个月,A组和B组胎儿出生后一般情况尚可,且都能得到较好的双心室纠治;C组出生后预后相对较差,需要早期手术,且以单心室姑息手术为主。结论:动脉导管血流逆向胎儿多合并复杂右心畸形,评估胎儿期动脉导管内血流可间接反映胎儿肺动脉及右心室发育程度,对右心系统畸形胎儿预后有较好的预测及治疗指导作用。