Chapter 20: Assessment of Fetal Age and Size in the Second and Third Trimester Flashcards
minimum distance between two bright echoes along the path of the ultrasound beam, which is half the spatial pulse length
axial resolution
Ratio of the BPD to the OFD
Cephalic Index
Fetus over 4,000 g ( 8lb 13 oz)
macrosomia
measurement from the frontal to the occipital obtained at the same level as the BPD
occipital-frontal diameter (OFD)
precision rate or the probability of disease
predictive value
expected birth date
estimated date of confinement
estimated delivery date
type of fetal age calculation that uses the first day of the last menstrual period rather than date of conception
gestational age
Differences in normal growth parameters
altitude
genetics
maternal smoking
each measurement type needs to be within a “cluster” ranging between <2mm and 3 mm
averaging of multiple measurements
two ways of listing fetal age in charts
list estimated age in weeks and days
use weeks and tenths of weeks
Fetal age is usually computed in _____
menstrual weeks
Normally conception takes place about ___ weeks after LMP
2
Birth normally occurs ___ weeks from LMP
40
LNMP
last normal menstrual period
Routine measurements for fetal parameters
BPD, HC, AC, length of at least one extremity long bone
parameters obtained early in gestation are so small that any error in measurement due to limits of resolutions in the sonographer instrument used to operator error will be relatively larger
multiple fetal parameter
used to estimate fetal ages and weights
polynomial formulas
BPD carries a smaller interobserver variance or error, usually <__mm
2
BPD has lesser reliability after the ___ menstrual week
33
The BPD is measured from ____ skill table to _____ skull table
outer
inner
BPD can be measured routinely from ___ weeks gestation
12
BPD accuracy of predictive value
+/- 3 weeks from 29 weeks to LMPB
BPD should be obtained before __ weeks after LMP
33
circumference =
d1 + d2 x 1.57
measured from outer edge to outer edge of middle of frontal bone and occipital bone echoes
OFD
CI=
BPD/FOD x 100
used to determine if shape of transverse fetal skull can allow a reliable BPD measurement
cephalic index
long and narrow head
short BPD measurement
CI below normal
dolicocephalic head
BPD relatively wide
FOD short
CI greater than normal
Brachycephalic
reverse oxycephaly
often occurs late in pregnany or when crowding of the fetus puts pressure on the vertex of the skull, causing shortening of the vertical dimension of the skull and widening of both diameters of the transverse plane which may not affect CI
platycephaly
the distance from the outer edges of left and right fetal eyes
binocular measurements
valuable indicator of fetal growth because it reflects the development of abdominal organs such as liver and spleen
abdominal circumference
The abdominal circumference should be measured at the level of the ______ with ______ and perpendicular to the _____.
umbilical junction
portal vein
spine
Favored view in AC demonstrates the confluence of the umbilical and portal veins in fetal liver called _______view.
hockey stick
Abdominal circumference =
1.57 x (d1 +d2)
accuracy of humerus, tibia, and ulna =
+/- 3 weeks at term
At term the accuracy of femur length is:
+/- 2.2 weeks
most commonly used parameter for estimating fetal age
femur length
Femur length can be reliably used after __ weeks gestation.
14
The recommended measurement of the humerus length
entire ossified portion of humerus to end of longest epicondyle
The ____ is the largest bone in the forearm and is medial in location
ulna
The ____ is the largest bone in the lower leg located medially.
tibia
forearm bones
ulna
radius
lower leg bones
tibia
fibula
one of the most often sought parameters of fetal growth
weight
associated with higher incidences of neonatal morbidity and death
low birth weight/IUGR
birth weight 4,000 g or higher
macrosomia
increase in weight prediction accuracy through measurement of soft tissue
3D imaging
Variables in weight
gestational age and sex
maternal height/weight at first visit
ethnic group
parity
smoking
variation of a theme that uses parameters of the fetal head and abdomen or other sonographer parameters to estimate the relative fat content, as well as size of head and liver, and fetus’s length
MFPs
The _____ is the most uniform organ
brain
Femur length is usually proportional to ______
fetal length
powerful statistical tool for comparing the relative sizes of two parameters
ratio or nidex
parameter that is the so called “standard”
denominator of ratio
Compartive numerator in a ratio becomes larger
ratio increases
Ratio percentage =
100(numerator/denominator)
transverse head circumference/abdominal circumference ratio
Abdomen to head ratio
The HC/AC ratio is normally __:__
1
1
The use of _____ average ages and the range of ages produce more accurate dates and are more likely to expose abnormal parameters or erroneous measurements that is the use of single fetal parameter
MFPs
Any two fetal parameter ages from the same examination should not have a range in weeks over __% of the fetal age.
20
All parameter ages from an examination should be with +/- __% of the average fetal parameter age.
10
Age estimates from fetal head parameters normally have about ____ the error (variance) of body parameter ages
half
Long-bone sonographic measurements should include:
only the osseus portions of the bone diaphysis
The fetal expected birth date is known as the EDC or:
EDD
The most accurate fetal measurement in the second and third trimesters can be obtained from:
a. the BPD
b. the AC and FL
c. the HC
d. multiple parameters
d
Which phase of pregnancy provides the most accurate dating?
a. early embryo measurements
b. Early second trimester, 16 to 18 weeks
c. Late second trimester, 25 to 26 weeks
d. Early third trimester, 28-29 weeks
a
The preferred measurement method for fetal growth is:
a. one single measurement
b. BPD, FL, AC, HL, HC
c. average of multiple measurements, three or more
d. HC, AC, FL
c
The normal duration of pregnancy is:
40 weeks from the LMP
Hadlock and coworkers and Ott determined the accurate indicator of fetal age is determined by:
a. single fetal parameter average age
b. FPA
c. multiple fetal parameter average age
d. femoral diaphysis length
c
The earliest successful BPD measurement can usually be secured at week:
12
If the cerebellum is seen in a BPD measurement, the plane is _____ in the posterior portion of the image.
too low
The most common and routine measurements to assess the fetal growth and well-being are:
BPD, AC, HC, and FL
Select a fetal characteristic that is not a late gestational individuation.
a. elongated fetus
b. dolicocephaly
c. thin fetus
d. bradycardia
d
What structures are seen in an accurate BPD measurement?
complete oval calvarium, sphenoid and petrous bones
To estimate an accurate fetal age, the BPD measurement should be obtained before:
33 weeks
An HC measurement should be obtained:
a. using the inner edge of the calvarium at the level of the BPD
b. using the outer edge of the calvarium at the level of the BPD
c. using the outer edge of the calvarium at the level of the cerbellum
d. at the level of the occipital circumference
b
What is the CI formula?
BPD/FOD x 100
Platycephaly is:
a. premature closure of the cranial sutures
b. flattening of the forehead, causing skull widening
c. a type of coneheadedness
d. shortening of the vertical dimension of the skull
d
The most exact of the orbit measurements is the:
BOD
All of the following are fetal long bones except:
a. tibia
b. humerus
c. metacarpal
d. ulna
c
Fetal weight by ultrasound is frequently requested to rule out all except:
a. macrosomia
b. BPP
c. IUGR
d. possible low birth weight
b
If the umbilical/portal junction is not visualized while attempting an AC measurement, use the level of the fetal:
stomach
Preferred technique for measuring the fetal abdomen and head circumference is:
ellipse
Two purposes for second and third trimesters of a fetus are estimating _____ and determining the size and development.
fetal age
Differences in fetal growth parameters can be caused by maternal _____, ______, and genetics.
smoking
altitude
Normally conception takes place about ___ weeks after the LMP
2
Molding and normal morphologic variations of the fetal head have a great effect on the accuracy of the _____ measurement in assessing age.
BPD
Exclude the _____ of the scalp when measuring from the leading edge of the parietal bone for a BPD measurement.
soft tissue
When taking fetal measurements, always use the transducer and focal range that provide the _____ resolution
best
Macrosomia equates to a fetus over _____ g.
4,000
If the fetal head is very low in the pelvis a(n) ______ transducer may allow accurate BPD measurements.
endovaginal
The head circumference should be measured on the same image used for the ___ measurement.
BPD
The more measurements obtained and averaged during a fetal ultrasound, the more _____ the fetal age estimate.
accurate
MFP (____) is the average gestational age determined by four common measurements of the fetus.
multifetal parameters
A measurement of the HC using the perimeter tracing method should be around the _____ edge of the calvarium.
outer
A fetus with a long and narrow head is called ______.
dochiocephalic
Cerebellar size is generally unaffected by fetal _____ disturbances and is independent of the shape of the ____.
growth
cranium
A correct AC measurement demonstrates the _____ vein junction with the _____ vein perpendicular to the ____.
umbilical
portal
spine
A structure within the cranium that maintains a relationship to fetal growth throughout pregnancy is the _____.
cerebellum
Common fetal body ratios are ___, ____, and ««<
FL
BPD
AC
The recommended technique to obtaining an accurate AC is to first locate the long axis of the _____.
fetal spine
The outer ____ line must be included in the abdominal circumference so that AC is not underestimated.
skin
The femur measurement can be reliably used after ____ weeks gestation.
14
Cerebellar hypoplasia with herniation into the spinal canal describes which of the following malformations?
a. Type IV Arnold Chiari malformation
b. Classic Potter sequence
c. Type II holoproscencephaly
d. Type III agenesis of the corpus callosum
a
Choose the head end of the neural tube
a. nomogram
b. rachsischisis
c. rostral
d. neuropore
c
Choose the sonographic appearance of a cephalocele
a. macrocephaly
b. nuchal ligament forming a midline segment
c. complex paracranial mass
d. located in the anterior portion of the neck
c
Cranial anatomy is routinely visualized after how many gestational weeks?
12-14
Define brachcephaly
short broad head caused by premature fusion
During a sonographic examination, a wide high third ventricle, teardrop shaped ventricle, a widened ventricular atria, absent cavum septi pellucida, and a sunburst appearance of the gyri and suli were imaged in the fetal brain. What malformation do these findings support?
Agenesis of the corpus callosum
Increased AFP is due to:
open spinal defect
ventral wall defect
Down syndrome
Lissencephaly is an absence or paucity of gyri resulting in the characteristic appearance of:
a smooth cerebral surface after 20 weeks
Select the correct method to measure a BPD
a. transverse, lateral inner to inner
b. longitudinal, sagittal outer to outer
c. transverse, lateral outer to inner
d. longitudinal front to back
c
Select the meaurement from the frontal to the occipital bone obtained at the level of the thalami.
a. Biparietal diameter (BPD)
b. Cephalic index (CI)
c. Occipitofrontal diameter (OFD)
d. Binocular distance (BOD)
c
Select the sonographic features of semilobar holoproscencephaly
a. incomplete fusion of the thalami, microcephaly, partial separation of the hemispheres and ventricles
b. single ventricle, absent falx and corpus callosum, hypotelorism
c. clubfoot, polyhydramnios, frog-like eyes, abnormally shaped cephalic pole
d. herniation of the posterior fossa into the foramen magnum, hydrocephalus
a
The metencephalon and myelencephalon are part of the:
rhombencephalon
The most frequent anomaly noted with cleft palate or cleft lip is:
club foot
What is the ratio of the BPD and OFD called?
Cephalic index (CI)
Which anatomic landmarks help determine the correct level to measure the HC?
a. peduncles, cisterna magna, ventricles
b. thalamus, falx, cavum septum pellucidum
c. third ventricle, thalamus, cerebellum
d. cerebellum, parietal bones, medulla oblongata
b
Which cranial bones are the landmark for the measurement of the BPD?
a. parietal bones
b. occipital bones
c. frontal bones
d. sphenoid bones
a
Which of the following abnormalities is most commonly associated with cystic hygroma?
a. spina-bifida
b. beckwith-weidemann syndrome
c. turner syndrome
d. dandy walker syndrome
c
Which of the following central nervous system malformations is identifiable in the first trimester?
a. omphalocele
b. spina bifida
c. ectopia cordia
d. cystic hygroma
b
Which of the following demonstrates cystic dilatation of the fourth ventricles?
a. Type III Arnold-Chiari malformation
b. Dandy-Walker malformation
c. Lobar holoprosencephaly
d. anencephaly
b
Which of the following is a sonographic feature of anencephaly?
a. large cisterna magna
b. cyclopia
c. fused thalami
d. frogeyes
d
Which of the following is the congenital absence of one or both eyes?
a. dysgenesis
b. anophthalmia
c. myeloschisis
d. retrognathia
b
The central portion of the cerebellum between the hemispheres is termed the _____
vermis
_____ is a congenital brain anomaly resulting from a migrational defect of the occipital horns of the lateral ventricles leading to ventricular enlargement.
colpocephaly
_____ is abnormally formed organs
dysgenesis
_____ is a substance that interferes with embryonic development.
teratogen
The forebrain is also known as the _____
prosencephalon
The great cerebral vein is also called _____
the vein of galen
The third ventricle is positioned between the ____ and the frontal horns of the lateral ventricles.
thalami
The presence of a single median bony orbit with a fleshy proboscis above it is _____
cyclopia
Many brain structures develop between week ______, resulting in this time frame being identified as the critical period of brain development.
3 and 16
_____ is an abnormal increase in the volume of the cerebral ventricles
ventriculomegaly
A sonolucent area in the choroid plexus is known as _____
choroid plexus cyst
______ is the most severe form of holoprosencephaly
alobar
The most severe form of arnold-chiari malformation is ____
type III
_____ is the most common type of intracranial hemorrhage seen in the fetus
intraventricular hemorrhage
