Test 3 Flashcards
when does pregnancy enter the second trimester?
after the first 12 weeks of pregnancy
by 20 weeks, what are the primary biometric parameters?
- biparietal diameter
- head circumference
- abdominal circumference
- femur length
when does a fetus enter the growth stage of pregnancy?
after midterm or 20 weeks gestational weeks?
what are measurements in thr 2nd and 3rd trimester more accurate for?
gestational size rather than age
what is considered to be one of the best predictors for gestational age?
BPD
what is the BPD?
a biometric measurement preformed in the transaxial view of the fetal head just above the level of the ears
how is the sound beam faced when looking for BPD?
from the lateral aspect of the fetal head, with the sound beam perpindicular to the interhemispheric fissue, also known as the cerebral falx
what should be seen when looking for BPD near the center of the cranium?
the diamond shaped hypoechoic thalmus
what should the BPD not show?
orbital rims anteriorly or the cerebellum posteriorly
how should the calipers be placed for BPD?
placed on the outer edge of the near fiels cranium and the inner edge of the far-field cranium
what is brachycephaly?
an abnormally widened BPD
what is dolichocephaly?
an abnormally shortened BPD
what plane is used when calculating head circumferance?
same as BPD
how should the ellipse tracing be placed for head circumferance?
placed along the outer border of the fetal cranium and should not include the soft tissues of the fetal scalp
why is HC helpful in cases of abnormal fetal head shape?
becuase it is least influenced by shape
what is calculation of AC used for?
estimation of fetal size or weight
how should the AC be obtained?
with the true transverse plane of the fetal abdomen at the level of the umbilical vein junction with the left portal vein
what should not be seen in the image of the AC?
kidneys should not be seen
what are the limitations for assessment of gestatinal age?
- fetal crowding can alter the fetal abdomen shape and its size
- oligohydramnois and advanced gestational age may influence the AC
- the fetal abdomen also has a large variation during the 3rd trimester because of biologic influences
- fetal AC is influenced more by fetal size than fetal age, especially in the 3rd trimester
can gestational age be relied on by the AC?
no, particullary in the 3rd trimester
what is the second to the BPD in accuracy for prediction of gestational age in the 2nd trimester?
femur length
what is least affected by surrounding structure?
femur length
should both or 1 femur be visualized be examined?
both femurs in the presence of ossification and gross symmetry
what femur should be examined?
the femur closest to the trasducer
how may occipital frontal diameter (OFD) be used?
may be used along with the BPD to determine the fetal head shape and size
what is the cephalic index calculation?
CI=(BPD/OFD) x 100
what is a normal cephlaic index?
76 to 84
what does a high cephalic index indicate?
brachycephalic
what does a low cephalic index indicate?
dolichocephalic
how is OFD demonstrated?
by the caliper line over the cerebral falx
what is the binocular measurement?
measurement across the distance of both orbital rims
what may binocular measurment assist in diagnosing?
facial abnormalities such as:
- hypotelorism
- hypertelorism
what is the transcerebellar (TCD) measurment?
the posterior fossa region of the fetal head evaluated for evidence of pathology (cerebellar hypoplasia)
what may be used as a secondary biometric measurement to assess gestational age?
TCD
what can be visualized when measureing the TCD?
- cerebellum
- cerebral peduncles
- thalmus
how are the cerebrellar hemispheres identified?
as 2 hypoechoic circular structures with echogenic borders on both sides of midline
what is the vermis?
brightly echogenic wedge shaped between the cerebellar hemispheres
what are the other structures included in the posterior fossa?
- cisterna magna
- nuchal fold
when does the cerebral hemispheres correlate with gestational age?
between 15-25 weeks
what is the cisterna magna?
anechoic space located in the posterior fossa immediately posterior to the cerebellum
what may an abnormal sized cisterna magna (1cm) suggest?
- ventriculomegaly
- cerebellar hypoplasia
- dandy-walker malformation
what is absence of obliteration of the cisterna magna associated with?
fetal spinal dysraphism
what is the nuchal fold measured for?
in the 2nd trimester to identify a risk for trisomy 21
what is the nuchal fold?
skin at the posterior edge of the fetal cranium
what measurments of nuchal fold suggest trisomy 21?
thickness of 5-6mm or more between weeks 18 and 24
where is the atrium of the lateral ventricle located?
inferior to the level of the BPD
what is the atrium of the lateral ventricle?
junction of the anterior, occipital, and temporal horns
what is the measuerment of the atrium of the lateral ventricles?
6-10mm throughout pregnancy
what does the choroid plexus produce?
CSF
what does thoracic circumferance get measured for?
diagnosis of potentially lethal fetal abnormalities
what can comparison of thoracic and abdominal provide information about?
skeletal dysplasias
what may an abnormally small thoracic to AC ratio assist in the assessment of?
risk of pulmonary hypoplasia
what is the normal heart circuferance>
1/3 of the thoracic circumferance
what does biophysical profile indirectly test for?
fetal hypoxia
how long is the fetus observed for in biophysical profile?
30 minutes
what are the 5 parameters assesed in biophysical profile?
- fetal tone
- fetal breathing
- body movements
- amniotic fluid volume
- nonstress test or placenta grade
placental grading-grade 0
<18 weeks
placental grading-grade 1
occasional parenchymal calcification (18-29 wks)
placental grading-grade 2
occasional basal calcifications with indentations of chorionic plate
placental grading-grade 3
significant basal calcifications with chorionic plate indentations to the basal layer (>39 wks)
what is fetal tone?
one complete episode of flexion to extension and back to flexion
what is fetal movement?
three seperate fetal movements within 30 minutes
what is fetal breathing movement?
movement of the diaphragm >30s
what is amniotic fluid volume?
amniotic pocket >2cm OR
amniotic fluid index >5cm
what is a nonstress test?
exhibits two fetal heart accelerations within 20 min or placental grade >2
what are the total points in biophysical test?
> 8
what are markers for acute fetal hypoxia?
- nonstress findings
- fetal tone
- breathing and body movements
what is a marker for chronic fetal hypoxia?
amniotic fluid volume
what is fetal presentation?
realtionship of the fetal head with the internal cervical os
when does fetal position change less frequently?
after 34 weeks
what is cephalic or vertex position?
fetal head lies most inferior, closest to the cervical os
what is the transverse postion?
- fetal head and body lie across the maternal abdomen
- check for signs of placenta previa
what is the oblique presentation?
-fetal head and body are lying at a 45 degree angle to the maternal sag plane
what is breech presentation?
- fetal head located in the superior portion of the uterus
- presenting part should be determines after 36 weeks gestation
what is frank breech presentation?
- fetal buttocks are presenting with the feet near head
- hips flexed and knees extended (most common)
what is complete breech presentation?
- fetal buttocks are presenting with the knees bent and feet down
- both hips and knees are flexed ( most common)
what is an incomplete breech presentation?
- footling breech-fetal foot is the presenting part
- one or both hips and knees are extended
- greatest risk for prolapsed cord
