OB/GYNE - Chapter 50 (100% Error-free answers)
Fetal biometry correct answers - Biparietal diameter
- Head circumference
- Abdominal circumference
- Femur length
Biparietal diameter correct answers - In second trimester this is accepted as the single most
accurate measurement to estimate fetal age
- In third trimester can be difficult due to position of head low in the pelvis
- Between 17-26 weeks the predictive value is +/- 11 days in 95% of population
- By the end of third trimester, predictive values decrease to +/- 3 weeks
- Head should be imaged in transverse view with parietal bones in near field and far field
- BPD taken perpendicular to the fetal skull at the level of the falx, thalamus, and cavum septum
pellucidum
- Fetal head should be ovoid shape not round
- Caliper should be placed at leading edge of parietal bone to leading edge of the opposite
parietal bone (AKA outer to inner), perpendicular to falx, soft tissue should not be included
- If proper landmarks cannot be visualized due to early age (too late for CRL, too late for BPD),
the following landmarks can be used: smooth symmetric head, visible choroid plexus, and a
well-defined midline echo that is an equal distance between both parietal bones
Head circumference correct answers - HC is taken at the same level as the BPD (can be
measured on the same image as BPD)
- Calipers should be placed on outside of skull bone, NOT to include the soft tissue (AKA outer
to outer)
- Prenatal compression of the fetal skull is common -- commonly due to malpresentation
(breech), crowding (multiples), or fibroids
Dolichocephaly correct answers - Head is shortened in the transverse plane (BPD) and elongated
in the anteroposterior plane
- Underestimates fetal age
Brachycephaly correct answers - Head is elongated in the transverse diameter (BPD) and
shortened in the anteroposterior diameter
- Overestimates fetal age
Cephalic index correct answers - Measurement used to normalize fetal head shape assessment
- BPD/OFD x 100 = CI (%)
- BPD = biparietal diameter; side to side
- OFD = occipitofrontal diameter; front to back
- Range of normal CI = 75-85%
- CI greater than 85% suggests brachycephaly
- CI less than 75% suggests dolichocephaly
Fetal biometry correct answers - Biparietal diameter
- Head circumference
- Abdominal circumference
- Femur length
Biparietal diameter correct answers - In second trimester this is accepted as the single most
accurate measurement to estimate fetal age
- In third trimester can be difficult due to position of head low in the pelvis
- Between 17-26 weeks the predictive value is +/- 11 days in 95% of population
- By the end of third trimester, predictive values decrease to +/- 3 weeks
- Head should be imaged in transverse view with parietal bones in near field and far field
- BPD taken perpendicular to the fetal skull at the level of the falx, thalamus, and cavum septum
pellucidum
- Fetal head should be ovoid shape not round
- Caliper should be placed at leading edge of parietal bone to leading edge of the opposite
parietal bone (AKA outer to inner), perpendicular to falx, soft tissue should not be included
- If proper landmarks cannot be visualized due to early age (too late for CRL, too late for BPD),
the following landmarks can be used: smooth symmetric head, visible choroid plexus, and a
well-defined midline echo that is an equal distance between both parietal bones
Head circumference correct answers - HC is taken at the same level as the BPD (can be
measured on the same image as BPD)
- Calipers should be placed on outside of skull bone, NOT to include the soft tissue (AKA outer
to outer)
- Prenatal compression of the fetal skull is common -- commonly due to malpresentation
(breech), crowding (multiples), or fibroids
Dolichocephaly correct answers - Head is shortened in the transverse plane (BPD) and elongated
in the anteroposterior plane
- Underestimates fetal age
Brachycephaly correct answers - Head is elongated in the transverse diameter (BPD) and
shortened in the anteroposterior diameter
- Overestimates fetal age
Cephalic index correct answers - Measurement used to normalize fetal head shape assessment
- BPD/OFD x 100 = CI (%)
- BPD = biparietal diameter; side to side
- OFD = occipitofrontal diameter; front to back
- Range of normal CI = 75-85%
- CI greater than 85% suggests brachycephaly
- CI less than 75% suggests dolichocephaly
