Umbilical Cord, Amniotic Fluid, Fetal Membranes Flashcards
What is the umbilical cord covered by?
amniotic membrane
How many vessels does the umbilical cord contain and what substance surrounds them?
two arteries, one vein
Wharton’s jelly; myxomatous connective tissue that protects vessels from tangling and being smashed
What is the normal size of the umbilical cord and when is it measured?
diameter: 1 to 2 cm
length: 40 to 60 cm
measured post labor
Describe the appearance and location of the ductus venosus.
Appears as thin intrahepatic channel with echogenic walls; lies in groove between left lobe and caudate lobe
patent during fetal life until shortly after birth when it transforms into the ligamentum venosum (second week after birth)
What length is the umbilical cord when it is considered short?
measuring less than 35 cm
What is an abnormal umbilical cord length associated with?
oligohydramnios, restricted space, intrinsic fetal anomaly, tethering of the fetus by amniotic band, inadequate fetal descent, cord compression, fetal distress
Is coiling of the umbilical cord normal or abnormal?
normal and related to fetal activity; usually coils to the left and near fetal insertion site
if coiling not seen, indirect sign of fetal distress
A short umbilical cord can lead to other obstetric problems such as…
preterm delivery, decreased heart rate during delivery, meconium staining secondary to fetal distress, fetal anomalies
When is omphalocele always present?
if cord is completely atretic (fetus attached directly to placenta at umbilicus)
What is the measurement of a long cord?
greater than 80 cm
What is associated with a long umbilical cord?
polyhydramnios, nuchal cord, true cord knots, umbilical cord compression, cord presentation, prolapse of cord, umbilical cord stricture or torsion resulting from excessive fetal motion
What is the size of an umbilical cord mass and when do they resolve?
generally less than 2 cm near fetal end of cord; resolved by second trimester (if not, associated with fetal anomalies and aneuploidy)
What masses are associated with the umbilical cord?
omphalocele, gastroschisis, umbilical herniation, teratoma of umbilical cord, aneurysm of cord, varix of cord, hematoma of cord, true knot of cord, angioma of cord, thrombosis of cord secondary to compression or kinking
Describe thrombosis of umbilical vessels and it’s risk factor.
occlusion of one or more cord vessels
primarily occurs in umbilical vein
incidence higher in infants of diabetic mothers
Why does thrombosis of the cord occur?
it is primary or secondary to torsion, knotting, looping, compressions, or hematoma
What are the maternal factors for thrombosis of the cord vessels?
phlebitis and arteritis
What should the sonographer look for in thrombosis of cord vessels?
aneurysmal dilation of cord and presence of fetal hydrops
True knots….
knots may be single or multiple and with an increased incidence of congenital anomalies
What may true knots be associated with?
long cords, polyhydramnios, intrauterine growth restriction, monoamniotic twins
When may true knots be formed?
when loop of cord slipped over infant’s head or shoulders during delivery
What are false knots?
seen when blood vessels are longer than cord
often folded on themselves and produce nodulations on surface of cord
What is the most common entanglement in the fetus?
nuchal cord
What is the nuchal cord?
multiple coils around the fetal neck
How often is a single umbilical artery?
occurs in 0.08 to 1.9% of singleton births and 3.5% of twin pregnancies
more frequent in miscarriages and autopsy series
What has a single umbilical artery been associated with?
congenital anomalies (20-50%), increased incidence of intrauterine growth restriction, increased perinatal mortality, increased incidence of chromosomal abnormalities
What organ systems can a single umbilical artery affect?
musculoskeletal (23%), genitourinary (20%), cardiovascular (19%)
gastrointestinal (10%), central nervous system (8%)
What is an aneurysm and varix?
focal dilation of umbilical vessels affecting umbilical artery and vein
nearly always intraabdominal, extrahepatic in location
What does a dilation of umbilical vessels look like sonographicaly?
appears as dilated intraabdominal, extrahepatic portion of umbilical vein; color Doppler shows continuity with umbilical vein
What is the prognosis of umbilical vessel dilation?
usually a normal outcome
What are the functions of amniotic fluid?
acts as cushion to protect fetus, allows embryonic and fetal movements, prevents adherence of amnion to embryo, allows symmetric growth, maintains constant temperature, acts as reservoir to fetal metabolites before excretion by maternal system
Where is amniotic fluid produced?
by umbilical cord, membranes (1st trimester), lungs, skin, and kidneys (main production in 2nd trimester)
In the second half of pregnancy, what accounts for almost total volume of amniotic fluid?
fetal urination
=kidney function
As fetus and placenta mature, AF production and consumption change. What are these changes?
movement of fluid across chorion frondosum and fetal skin; fetal urine output and fetal swallowing; GI absorption
What is chorion frondosum?
portion of chorion that develops into fetal portion of placenta;
What happens at the chorion frondosum?
site where water exchanged freely between fetal blood and AF across amnion
When is the amount of urine produced the most significant?
at 18 to 20 weeks gestation
What is accomplished with the fetal skin being permeable to water and solutes and how long does this take place for?
allows direct exchange between fetus and AF until keritinization occurs at 24-26 weeks
When does fetal production of urine and the ability to swallow begin? What does this signify?
between 8 and 11 weeks
reflection of nervous system development and renal function
What is the function of keritin in skin cells?
it makes the skin resistant to water
What accounts for nearly total volume of AF by second half of pregnancy?
fetal urination - directly related to kidney function
If there is little to no AF, what could be the reason why?
fetus could have malformed kidneys or renal agenesis; fetus swallows AF, which is absorbed by digestive tract
What is the amount of AF regulated by?
production of fluid, removal of fluid by swallowing, fluid exchange within lungs, membranes and cord
How do the lungs rely on AF?
normal lung development depends on exchange of AF within lungs
What can happen if the AF is severely low? And what is the result?
inadequate lung development
fetus at high risk for developing small, or hypoplastic, lungs
Why does AF volume increase rapidly during the first trimester?
the fetus swallows fluid and it gets reabsorbed by the GI tract and is recirculated through the kidneys;
this results in increased AF production in first trimester
By 20 weeks gestation, AF volume increases by how much? And why?
10 mL/day
fluid produced by fetal urination slightly exceeds amount removed by fetal swallowing
Abnormalities of the fluid may…
interfere with normal fetal development, cause structural abnormalities, be an indirect sign of underlying anomaly
What anomalies could be associated with fluid abnormalities?
neural tube defect, gastrointestinal disorder, renal anomalies
How does a sonographer assess AF?
scan through the entire uterus and “eyeball” the fluid present, lie of fetus, and position of placenta
Describe how the amniotic fluid index obtained?
the uterine cavity is divided into four equal quadrants by two imaginary lines running perpendicular to each other; the largest vertical pocket of AF, excluding fetal limbs or umbilical cord loops, is measured
What AFI values are considered low, normal, and high?
5-10 cm = low fluid
10-20 cm = normal AF
20-24 cm = increased fluid
What is oligohydramnios defined as with AFI?
AFI less than 5 cm
largest vertical pocket measuring 2 cm or less
What is polyhydramnios defined as with AFI?
AFI greater than 24 cm
largest vertical pocket measuring 8 cm or more
What are considered low, normal, and high fluid pocket levels?
less than 2 cm = oligohydramnios
2 to 8 cm = normal AF
greater than 8 cm = polyhydramnios
What is a single pocket assessment?
maximum vertical pocket assessment of AF done by identifying largest pocket of AF
What is a two-diameter pocket assessment?
it uses largest pocket of AF
horizontal and vertical dimensions of the maximum vertical pocket are multiplied together to obtain a single volume
With a two diameter pocket assessment, what is considered normal?
15 to 50 cm
What type of pregnancies have a slightly lower median AFI value?
twin pregnancies have a slightly lower median AFI value than singleton pregnancies
What is polyhydramnios defined as with AF?
defined as AF volume of greater than 2000 mL
2L
What is polyhydramnios associated with?
increased perinatal mortality and morbidity and maternal complications
also central nervous system disorders and/or gastrointestinal problems
What does the patient present clinically and why is sonography ordered?
What are maternal symptoms for polyhydramnios?
patient will present with clinical findings of uterus greater than dates
sonography ordered to rule out multiple gestation, molar pregnancy, or fetal size greater than dates
acute onset may be painful, compress other organs/vascular structures, cause hyponephorosis, produce shortness of breath
What can a CNS disorder cause?
depressed swallowing
What do GI abnormalities result in?
ineffective swallowing that are often caused by a blockage (atresia) of the esophagus, stomach, duodenum, or small bowel
What types of maternal conditions are associated with polyhydramnios?
diabetes mellitus, obesity, Rh incompatibility, anemia, congestive cardiac failure
What are the sonographic findings for polyhydramnios?
free floating fetus with swollen amniotic cavity, accentuated fetal anatomy, AFI of 20 cm or greater
What is oligohydramnios?
overall reduction in amount of AF resulting in fetal crowding and decreased fetal movement
In the second trimester, what is the prognosis of oligohydramnios?
poor; even if maternal serum alpha-fetoprotein is elevated
What can the development of oligohydramnios be attributed to?
congenital anomalies (specifically kidneys, obstruction of urine), IUGR, post term pregnancies, rupture of membranes, iatrogenesis
What may produce growth restriction and oligohydranmnios?
fetal hypoxemia and placental insufficiency
There is a ___fold increased risk of growth delay when oligohydramnios is present
four fold increase
What does placental insufficiency result in?
decreased kidney function (produces redistribution of fetal blood flow away from kidneys and toward brain to counterattack hypoxia)
decreased urine output, which decreases fluid volume
Oligohydramnios is a common complication of what?
postdate pregnancies
diminished placental function and arterial redistribution of fetal blood flow with brain sparing effect
What are iatrogenic causes of oligohydramnios?
medications, insensible fluid loss, maternal intravascular fluid depletion, prior procedures such as chorionic villi sampling, amniocentesis
What specific medications cause oligohydramnios?
nonsteroidal antiinflammatory drugs, angiotensin-converting enzyme inhibitors, calcium channel blockers, nitrous oxide
What are nonanomalous causes of oligohydramnios?
IUGR, premature rupture of membranes, postdate pregnancy (42 weeks), chorionic villius sampling
What are fetal anomalous conditions related to oligohydramnios?
infantile ploycystic kidney disease, renal agenesis, posterior urethral valve syndrome (more common in males), dysplastic kidneys, chromosomal abnormalities
What is amniotic band syndrome?
a common, non-recurrent cause of various fetal malformations involving limbs, craniofacial regions, trunk
associated with abnormality in fetal membranes
What are other names for amniotic band syndrome?
ADAM complex (amniotic deformities, adhesion, mutilation), amniotic band sequence, aberrant tissue bands, congenital constricting bands
What are common findings with amniotic band syndromes?
facial clefts, asymmetric encephaloceles, constriction or amputation defects of extremities, clubfoot deformities
What can predict amniotic band syndrome?
amniotic bands that entangle or amputate fetal parts
What are the sonographic findings for ABS?
following the band closely with real time scanning, the sonographer can observe where the band is attached to the uterine wall and what, if any, constriction is placed on the fetus
What are amniotic sheets?
amniotic sheets, shelves, or folds identified as echogenic, nonfloating bands crossing through amniotic cavity
are thicker than bands associated with amniotic band syndrome
What do amniotic sheets signify?
uterine synechia
What are uterine sheets caused by?
uterine scars from previous instrumentation used in uterus, c-sections, episodes of endometritis
Who is at risk for developing uterine scars?
patients with history of endometrial D&C, intrauterine infections, endometritis, removal of fibroids or endometrial polyps, or prior c-sections
What are the sonographic findings for amniotic sheets?
fine echo dense line in uterine cavity separated from uterine wall by echo-lucent space, membrane may either completely surround fetus or be freely movable in amniotic cavity, can appear anywhere in uterine or cervical cavity, seen extending from one side of uterus to other, oblique across uterus or as multiple echogenic lines
Where does a thrombosus of the umbilical vessels primarily occur?
umbilical vein
When is the largest amount of AF fluid seen?
between 20 and 30 weeks gestation
At the end of pregnancy, there are particles (fatty substance) in the AF. What is this?
vernix caseosa
