fetal circulation


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fetal

 [fe´t'l]
of or pertaining to a fetus or to the period of its development.
fetal acoustic stimulation test a test used to assess fetal health in compromised pregnancies; a vibroacoustic stimulus such as an electronic artificial larynx is applied either externally or directly to the fetus and resultant fetal movements, cardioacceleration, and alterations in respiration are compared to those of normal fetuses.
fetal alcohol syndrome a group of symptoms characterized by mental and physical abnormalities of the infant and linked to the maternal intake of alcohol during pregnancy. Clinical manifestations, which can be present in varying degrees, include prenatal and postnatal growth deficiency, mental retardation, irritability in infancy, hyperactivity in childhood, microcephaly, short palpebral fissures, smooth philtrum, thin vermilion border of upper lip, small distal phalanges, and ventricular septal defects. Although the exact amount of alcohol consumption that will produce fetal damage is unknown, the risk and extent of abnormalities are most likely to be increased when the daily intake of pure alcohol exceeds 2 ounces. The periods of gestation during which the alcohol is most likely to result in fetal damage are three to four and a half months after conception and during the last trimester. Abstinence from alcohol during pregnancy is recommended.
fetal assessment determination of the well-being of the fetus; techniques and procedures include: (1) medical and nursing histories and physical examination of the mother, (2) assays of amniotic fluid obtained by amniocentesis, (3) ultrasonography, (4) chemical assessment of placental function, (5) electronic and ultrasonic fetal heart rate monitoring, and (6) chorionic villus sampling. Extensive and thorough assessment of the health status of the fetus is indicated when maternal characteristics, obstetrical complications, and familial and genetic factors place the fetus at risk.

Amniotic fluid assay is most often done to establish the diagnosis of a genetic disorder, to monitor the fetus sensitized against the mother's rh factor, or to determine fetal lung maturity. Cells floating in the amniotic fluid sample can be examined to detect genetic disorders caused by chromosomal abnormalities and to detect certain metabolic aberrations. neural tube defects such as spina bifida and anencephaly are detected by analyzing the amniotic fluid for alpha-fetoprotein (AFP). When an open neural tube defect is present, the amount of alpha-fetoprotein can be increased as much as eight times the normal value.

The amniotic fluid also can be assayed for bilirubin, an indicator of the severity of Rh incompatibility between maternal and fetal blood. Fetal lung maturity can be assessed by evaluating the presence of pulmonary surfactant, a phospholipid protein, in the amniotic fluid. In normal fetal development the production of surfactant, a substance essential to lung expansion and adequate ventilation after birth, begins at about the 22nd week of gestation; however, surfactant is not present in sufficient quantities until 35 to 36 weeks. Two of its principal constituents, lecithin and sphingomyelin, can be evaluated by measuring the lecithin-sphingomyelin ratio (L/S ratio) in a sample of amniotic fluid. In general, a ratio greater than 2:1 indicates that the fetal lungs are mature and the newborn infant is not likely to develop respiratory distress syndrome of the newborn.

Ultrasonography is a noninvasive technique helpful in diagnosing unusual fetal presentations, placenta previa, multiple pregnancy, and fetal abnormalities such as hydrocephalus and hydronephrosis. It also can be used to trace fetal growth by periodic measurement of the biparietal diameter of the head of the fetus, femur length, or head:abdominal circumference ratio.

Chorionic villus sampling is a technique by which a small sample is obtained from the fetal portion of the placenta by aspiration through the cervical canal. It can be used for diagnosis of genetic abnormalities as early as the first trimester.

Chemical assessment of the nutritive and respiratory functions of the placenta can be accomplished by determining the amount of the hormone estriol in the maternal blood or urine. Throughout gestation a normally functioning placenta produces increasing amounts of estriol, the precursors for the production of which are provided by the fetal adrenal glands. Thus, a normal estriol value in maternal blood or urine indicates that both the placenta and the fetus are healthy.

Fetal monitoring using either ultrasound or direct electronic monitoring equipment to measure fetal heart rate and uterine contractions and the nonstress test to evaluate fetal heart rate changes in response to uterine contractions and fetal movements are discussed under fetal monitoring.
fetal circulation the circulation of blood from the placenta to and through the fetus and back to the placenta. Fetal circulation can be traced as follows: The oxygenated blood is carried from the placenta to the fetus via the umbilical vein. About half of this blood passes through the hepatic capillaries and the rest flows through the ductus venosus into the inferior vena cava. Blood from the vena cava is mostly deflected through the foramen ovale into the left atrium, then to the left ventricle, into the ascending aorta and on to the head and upper body. The arterial oxygenation of this blood is approximately 25 to 28 mm Hg; thus the fetal coronary circulation and brain receive the blood with the highest level of oxygenation.

Deoxygenated blood from the superior vena cava flows into the right atrium, right ventricle, and then into the pulmonary artery. Because of high pulmonary vascular resistance, only about 5 to 10 per cent of the blood in the pulmonary artery flows to the lungs, the majority of it being shunted through the patent ductus arteriosus and then down the descending aorta. The PaO2 of the blood in the descending aorta is about 22 mm Hg.
Postnatal Changes. After birth the changes in circulation involve closure of three fetal channels, the ductus venosus, the foramen ovale, and the ductus arteriosus. The ductus venosus closes with the clamping of the umbilical cord and inhibition of blood flow through the umbilical vein. The foramen ovale functionally closes after the first few breaths as pressure within the left atrium rises above that in the right atrium. The ductus arteriosus constricts partly in response to higher arterial oxygen levels that occur after the first few breaths. Other postnatal changes include a decrease in pulmonary vascular resistance and a decrease in pulmonary artery pressure. These changes result in the transport of 100 per cent of the cardiac output from the right heart to the lungs for oxygenation and then to the left heart and thence to the aorta.
A simplified scheme of the fetal circulation. From Betz et al., 1994.
fetal monitoring continuous intrapartal monitoring of the fetal heart rate and uterine contractions for the purpose of reducing preventable fetal and neonatal death by more accurate diagnosis and correction of problems related to fetal distress during labor, such as compression of the umbilical cord or placental insufficiency.
Noninvasive (Indirect) Monitoring. The fetal heart rate is measured using the techniques of ultrasonography or phonocardiography. Evaluations of this kind provide good data on the fetal heart rate and, unlike direct fetal monitoring, can be used while the amniotic membranes are still intact and the cervix has not yet dilated. These techniques are easier to use than invasive techniques but do not provide information as accurate and precise as that obtained by direct monitoring.

The duration and relative strength of uterine contractions and the length of intervals between them can be measured externally by placing a tokodynamometer on the mother's abdomen at the site of greatest uterine activity. The force of contractions is displayed on a screen. Layers of fat in obese patients and restlessness of the mother interfere with precise external monitoring of uterine contractions. Therefore high-risk patients can be more effectively monitored by internal techniques.
Invasive (Direct) Monitoring. Invasive techniques of fetal and maternal monitoring require direct access to the fetus and amniotic sac via the vagina and dilated cervix. Direct electrocardiography of the fetal heart is accomplished by attaching an electrode to the fetal presenting part. Proper placement of the electrode makes the risk to the mother and fetus negligible, and the data obtained are extremely accurate. Direct monitoring of uterine contractions uses an intrauterine amniotic fluid catheter to measure intrauterine pressure changes.

Simultaneous monitoring of the fetal heart rate and uterine contractions is essential to accurate interpretation of events taking place within the uterus during labor. Patterns of a slowing heart rate (deceleration) or increase in rate (acceleration) are examined in the context of the phase of the contraction in which the change in rate occurs. For example, decelerations that take place early during uterine contractions may indicate compression of the fetal head, a normal and expected event. However, a deceleration occurring late in the contraction may indicate placental pathology and uteroplacental insufficiency, a very serious and life-threatening condition. However, maternal hypotension and uterine hypotonus, both of which can be alleviated or corrected, may also cause late deceleration.
Contraction Stress Tests:Oxytocin Challenge Test. The purpose of this test, which is usually not done before the 28th week of gestation, is to assess the respiratory function of the placenta; that is, to determine whether the placenta and fetus will be able to withstand the stress of repetitive contractions during labor, and if they cannot, when and how delivery of the infant should be carried out. It is indicated for high-risk mothers, such as those with diabetes, hypertensive disease of pregnancy, history of a previous stillbirth, or anything else affecting the health status of the fetus. The oxytocin challenge test should not be attempted if placenta previa is present or if the mother has had a previous delivery by midline-incision cesarean section.

Oxytocin is given to stimulate enough uterine contractions to provide a sample of fetal response and determine whether there is adequate placental respiratory reserve to maintain the fetus for the remainder of the pregnancy and through labor. Data from the recorded fetal heart rate patterns during contractions are used to assess the status of the fetus and to make decisions about either allowing the pregnancy to continue until the fetus is more mature, or intervening promptly to avoid severe and perhaps fatal stress on the fetus.

Prior to the administration of the oxytocin, the fetal heart rate is monitored for 30 minutes or more to determine baseline variability and fetal movement. Spontaneous movement of the fetus without oxytocin may mean it is not necessary. However, if there is no spontaneous movement, oxytocin is given in quantities sufficient to trigger three or four contractions.
Nipple Stimulation. This involves the application of warm, moist washcloths to the breasts, followed by 10 minutes of massaging and rolling of the nipples. If it is successful in inducing uterine contractions, it obviates the need for an oxytocin challenge test.
Nonstress Test. This test relies on spontaneous fetal activity rather than on oxytocin-induced fetal movement to assess fetal response to uterine contractions. If there is no spontaneous fetal activity, it may be elicited by external rubbing or gentle pressure on the mother's abdomen. Fetal heart rate is monitored externally and correlated with fetal activity. Acceleration of the heart rate can also be induced by vibroacoustic stimulation using an external source of sound such as an artificial larynx applied to the maternal abdomen over the fetal head. Increased confidence in the validity and accuracy of the nonstress test has led to its widespread use and, in many cases, its preference over the more time-consuming and often contraindicated oxytocin challenge test.
Accelerations and Decelerations. Periodic heart rate changes are evaluated in reference to a fetal “baseline” that is determined when there is no stress present. Deviations from the baseline occur in response to uterine contractions and fetal activity that affect fetal oxygenation and transfer of carbon dioxide.

Accelerations are transient increases of the fetal heart rate, occurring at the same time as uterine contractions and coming at anytime during labor. They may be the earliest indicators of fetal distress; however, without other abnormalities of fetal heart rate pattern, they are thought to be reassuring when in response to manipulation, stimulation, or fetal movement.

Decelerations are decreases in the fetal heart rate. The three types are early, late, and variable. Early deceleration is believed to be caused by fetal head compression. The fetal heart rate returns to the baseline at or before the end of the uterine contraction and is not associated with an abnormality. Late deceleration occurs after the uterus has begun to contract and may not cease with the contraction. It is an ominous sign of fetal distress, is believed to be caused by uteroplacental insufficiency, and is frequently associated with high-risk pregnancy and with maternal hypotension or uterine hyperactivity. Variable deceleration occurs at various times in relation to uterine contractions. It could be associated with umbilical cord compression and may be relieved by changing the mother's position.

Early signs that suggest fetal distress include irregularity and mild variable decelerations. Early signs of fetal compromise that are more ominous include further decreased variability, heart rate increased over baseline, and variable or late decelerations. Late signs of fetal distress include no variability, severe variable or late decelerations with minimal variability, bradycardia in relation to baseline heart rate, and a sinusoid pattern to the fetal heart rate.
External fetal monitoring. The heart rate of the fetus is evaluated, particularly in response to uterine activity or contractions. From Malarkey and McMorrow, 2000.

fe·tal cir·cu·la·tion

the circulation of the fetus in utero, with the placental circuit responsible for supplying oxygen and nutritive material and for eliminating CO2 and nitrogenous wastes.
See also: embryonic circulation.

fetal circulation

the pathway of blood circulation in the fetus. Oxygenated blood from the placenta travels through the umbilical vein to the heart. The blood enters the right atrium at a pressure sufficient to direct most of the flow across the atrium and through the foramen ovale into the left atrium; thus oxygenated blood is available for circulation through the left ventricle to the head and upper extremities. The blood returning from the head and arms enters the right atrium via the superior vena cava. It flows through the atrium at a relatively low pressure. Passing the tricuspid valve, it falls into the right ventricle, from which most of it is pumped through the pulmonary artery and the ductus arteriosus into the descending aorta for circulation to the lower parts of the body. A small amount of blood in the pulmonary artery is not shunted through the ductus and is carried to the lungs. The blood is returned to the placenta through the umbilical arteries.
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Fetal circulation

fetal circulation

Embryology Prenatal circulation which bypasses the lung and right heart, and is returned to the systemic circulation at the aorta via a patent ductus arteriosus, which usually closes at or shortly after birth, after which the blood flows to the lungs
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FETAL CIRCULATION
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FETAL CIRCULATION: Vessels that carry oxygenated blood are red

fetal circulation

The course of the flow of blood in a fetus. Oxygenated in the placenta, blood passes through the umbilical vein and ductus venosus to the inferior vena cava and thence to the right atrium. It then follows one of two courses: through the foramen ovale to the left atrium and thence through the aorta to the tissues, or through the right ventricle, pulmonary artery, and ductus arteriosus to the aorta and thence to the tissues. In either case the blood bypasses the lungs, which do not function before birth. Blood returns to the placenta through the umbilical arteries, which are continuations of the hypogastric arteries. At birth or shortly after, the ductus arteriosus and the foramen ovale close, establishing the postpartum circulation. If either fails to close, the baby may be hypoxemic.
See: illustration; patent ductus arteriosusillustration
See also: circulation

circulation

movement in a regular or circuitous course, returning to the point of origin, as the circulation of the blood through the heart and blood vessels. See also circulatory system.

antegrade circulation
circulation in the normal direction of flow.
artificial circulation
is maintained in cardiopulmonary arrest by cardiac compression.
collateral circulation
circulation carried on through secondary channels after obstruction of the principal channel supplying the part.
coronary circulation
that within the coronary vessels, which supply the muscle of the heart.
cutaneous circulation
cutaneous vessels are innervated by sympathetic adrenergic vasoconstrictor fibers; vasodilation is an important mechanism for losing heat after the body has been warmed.
enterohepatic circulation
the cycle in which bile salts and other substances excreted by the liver in the bile are absorbed by the intestinal mucosa and returned to the liver via the portal circulation.
extracorporeal circulation
circulation of blood outside the body, as through a hemodialyzer or an extracorporeal circulatory support unit.
fetal circulation
circulation of blood through the body of the fetus and to and from the placenta through the umbilical cord. See also fetal circulation.
hepatic circulation
includes the hepatic arterial blood supply and the supply from the portal vein; drainage is via the hepatic veins to the caudal vena cava.
lymph circulation
see lymph.
maternal circulation
the circulation of the dam during pregnancy, including especially that of the uterus.
micro-circulation
neonatal circulation
circulation in the newborn immediately after birth; the umbilical vessels contract forcing blood into the fetal veins; the foramen ovale closes, the ductus arteriosus narrows and eventually closes at day 1 to 2 after birth.
ocular circulation
consists of the uveal and retinal blood vessels supported by the aqueous humor and vitreous body.
placental circulation
consists of the umbilical arteries, the vessels of the placenta proper and the umbilical veins; approximates the fetal corporeal circulation in volume.
portal circulation
a general term denoting the circulation of blood through larger vessels from the capillaries of one organ to those of another; applied especially to the passage of blood from the gastrointestinal tract, pancreas and spleen through the portal vein to the liver.
pulmonary circulation
the flow of blood from the right ventricle through the pulmonary artery to the lungs, where carbon dioxide is exchanged for oxygen, and back through the pulmonary vein to the left atrium. See also pulmonary circulation.
splenic circulation
flow of blood through the splenic artery and arterioles to either the capillaries, e. g. white pulp, or the highly permeable sinuses of the red pulp. Splenic venous blood drains into the portal vein and passes through the liver before re-entering the general circulation.
systemic circulation
the flow of blood from the left ventricle through the aorta, carrying oxygen and nutrient material to all the tissues of the body, and returning through the superior and inferior venae cavae to the right atrium.
circulation time
the time required for blood to flow between two given points. It is determined by injecting a substance into a vein and then measuring the time required for it to reach a specific site.

fetal

of or pertaining to a fetus or to the period of its development.

fetal age
age of the fetus; this may be determined by its crown to rump length, and various other surface features such as hair follicles and eyelids.
fetal alcohol syndrome
in humans and laboratory animals; in laboratory animals manifested by small head and nose, narrow forehead, short palpebral fissures, long thin upper lip.
fetal circulation
the circulation of blood through the body of the fetus and to and from the placenta through the umbilical cord. Oxygenated blood from the placenta is carried to the fetus by the umbilical vein. The blood from the fetus is returned to the placenta by two umbilical arteries. Oxygenation of the fetal blood and disposal of its waste products is carried on through the placenta. When the lungs begin to function at birth some of the fetal vessels, such as the ductus arteriosus, and the fetal passages, such as the foramen ovale, begin to fall into disuse. This is a gradual process of fibrosis that takes place in the period after birth.
fetal crowding
too much fetal tissue in the uterus. May cause fetal retardation in some; also papyraceous fetus. Thought to cause some of the minor congenital deformities, e.g. carpal flexion in calves, facial distortion in foals.
fetal death
results in resorption, mummification or discharge to the exterior.
fetal death ratio
see fetal death ratio.
fetal dimensions
crown to rump (tail head) length; varies with species; useful as a guide to pregnancy duration.
fetal disease
disease of the fetus in utero.
fetal dropsy
in cattle may be due to inherited defect of lymph nodes and lymphatic drainage.
fetal dystocia
dystocia caused by some characteristic of the fetus, e.g. size, monstrosity, dropsy.
fetal early death
see early embryonic mortality.
fetal extractor
a device consisting of a breech bar that fits across the back of the cow's thighs below the vulva, with a 6 ft long rod with a ratchet running its length. A small tractor is levered along the ratchet and exerts traction on the calf via obstetric chains fitted to its feet. Has the advantages of a block and tackle but with the mobility of being fixed to the cow.
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Calving jack (fetal extractor) for use in a cow. By permission from Parkinson TJ, England GCW, Arthur GH, Arthur's Veterinary Reproduction and Obstetrics, Saunders, 2001
fetal fluids
the amniotic and allantoic fluids.
fetal giantism
due to prolonged gestation, although all prolonged gestations are not giants. Inherited in Holstein cows.
fetal hepatitis
focal or diffuse lesions in the fetal liver caused by bacteria or viruses, e.g. Tyzzer's disease, equine herpesvirus 1.
fetal maceration
sterile necrosis and dissolution of the fetus. May be ejected in this form or go on to mummification.
fetal malposition
presentation of the fetal parts in inappropriate positions for the easiest passage through the cervix, e.g. retention of the head, breech presentation.
fetal maternal rotation
alteration of the longitudinal relationship of the fetus to the dam effected per vaginam by manipulation with the hand or an obstetric crutch, or externally by casting the dam and rolling her from side to side while the fetus is held in position via a hand in the vagina.
fetal membranes
the membranes which protect the embryo and provide for its nutrition, respiration and excretion; the yolk sac (umbilical vesicle), allantois, amnion, chorion, decidua and placenta. See also extraembryonic membranes, placenta.
fetal membrane expulsion
occurs usually at the birth or less commonly within 12 hours; expulsion is by means of separation of the uterine attachment and contraction and involution of the uterine wall.
fetal membrane retention
see retained placenta.
fetal membrane slip
the sensation of a thread or edge of tissue slipping through the fingers when the amniotic vesicle in an early pregnant bovine uterus is grasped between the thumb and forefinger; the best indicator in a manual check for pregnancy until the time when cotyledons can be palpated.
fetal mobility
fetal movements during pregnancy.
fetal mole
see mole.
fetal monstrosities
fetal position
position of the fetus within the dam, described in terms of the dorsum of the fetus and the sector of the circumference of the dam's pelvis, e.g. dorsosacral, dorsoventral.
fetal posture
relationship of the movable extremities or appendages of the fetus to each other and the rest of the fetus, e.g. flexed neck.
fetal presentation
fetal rotation
a method of correcting uterine torsion in cows; the fetus is reached manually via the vagina and the fetus rotated around its long axis using a firm grasp on the upper part of a limb as a handle; the uterus, clinging to the fetus, rotates with it, undoing the torsion. Requires a fresh parturition, a slim but strong forearm and a nice appreciation of the physical law of torque.
fetal resorption
early death of the embryo during the fetal period with lysis and complete resorption of all of the products of the conception. The dam resumes normal estral cyclicity after a period of anestrus while there is maternal recognition of the pregnancy. See also early embryonic mortality.
fetal sex diagnosis
the karyotype of the fetus is determined from fetal cells collected from the amniotic fluid by amniocentesis.
References in periodicals archive ?
For nucleated maternal cell transfer into the fetal circulation, the proportion of cases with detectable maternal cell traffic into the fetal circulation was higher than those reported using less sensitive technologies, such as minisatellite analysis (14,33).
It is currently unknown whether the same rapid clearance kinetics could also be observed for maternal DNA clearance from the fetal circulation.
Transfer of nucleated maternal cells into fetal circulation during the second trimester of pregnancy [Letter].
We examined what proportion, if any, of the erythroblasts in the fetal circulation were TUNEL positive.
We conclude that >50% of the fetal erythroblasts in the fetal circulation and cord blood are TUNEL positive.
Newborn lung failure is typically associated with under development as a result of birth defects, damage, or persistent fetal circulation found in premature or full-term birth; adult lung dysfunction is more often the result of trauma.
The author explains the physiology of normal fetal circulation and the effects of congenital cardiac lesions, with particular reference to the interactions between the lesions and fetal cardiovascular development.
Sarah Garratt has been assessed at the Fetal Medicine Centre at Birmingham Women's Hospital and in-utero surgery has been performed to 'separate' the two fetal circulations.
Short term, effects of inhaled albuterol on maternal and fetal circulations.