Ch. 18 Fetal Biometry and Lie Flashcards
What is the most accurate measurement for determining gestational age?
Crown-rump length in the first trimester
Measurements taken in the second and third trimesters have a rang of aprox
+ or - 2 weeks
Term for how estimated due dates are determined from LMPs
Naegele’s Rule
What is Naegele’s rule
EDD=LMP - 3 months + 7 days
Term for a normal oval head shape
Mesocephaly
BPD measurements are not accurate at how many weeks
Accurate until 33 weeks
Which measurement is more accurate, HC or BPD?
HC, especially when dolichocephaly or brachycephaly is present
What measurement is the least reliable in determining gestational age
AC
Cephalic index (CI) defines head shape and is determined by
Dividing BPD by OFD (occipital-frontal diameter)
What is the normal range of CI
0.70 - 0.86 (70-86%)
Dolico CI would be
CI <70%
Brachycephaly CI would be
CI >86%
Term for an abnormally elongated head shape
dolichocephaly
Term for an abnormally rounded head shape
Brachycephaly
In cases of brachy or dolicocephaly, what should be disregarded
the BPD is eliminated from estimation of GA
The femur length is best obtained with what kind of transducer
Linear array
What portion of the femur should be measured and what should be excluded
Include only the ossified diaphysis, exclude the epiphyseal cartilage
When should skeletal dysplasia by considered in terms of the FL
When the FL falls more than 2 SD ratios below the mean
List other parameters that may be used to determine GA in cases of skeletal dysplasia when the bone measurements are inaccurate
Clavicular length, foot length (foot=femur length), binocular distance, transcerebellar distance
The system that is designed to detect fetal asphyxia
Biophysical profile (BPP)
What is the first ultrasound parameter in a BPP that will disappear with fetal hypoxia
Fetal breathing movements will be the first parameter to disappear in a BPP
What is the BPP criteria
30 seconds of breathing, 3 discrete gross body movements, 1 tone movement all within a 30-minute period and at least one pocket of amniotic fluid measuring 2 cm in the vertical axis (MVP) or an AFI of >5cm
What does NST stand for
Non-stress test. The demonstration of reactive FHR, consisting of 2 episodes of acceleration >15 BPM for 15 seconds over a 30 minute time frame (first NON US parameter to disappear with hypoxia)
In which type of cephalic presentation can vaginal delivery not occur
Brow cephalic presentation
Another term for cephalic is
Vertex
Describe all types of breech presentations
Footling - hips are extended, feet are presenting
Frank - hips are flexed and knees are extended. Legs in front of face
Complete - hips flexed, knees flexed
