2nd and 3rd trimester fetal assessment

BPD/HC

Axial view at level of 3rd vent, CSP and thalamus

Measure widest part of skull

Don’t include soft tissue

As the fetus ages, accuracy of fetal measurements for dating __________

Decreases

Fetal age derived from measurements should be within ___% average of fetal parameter age for that measurement

10

BDP is most accurate for dating before __ weeks

20

A slight ________ position may be helpful for evaluating fetal heads low in maternal pelvic

Trendelenburg

OFD

Perfomed at same level as BPD

Measure from anterior skull to posterior skull on outer edges

Cephalic index (CI)

Fetal head shape can be affected by molding or position, oligohydramnios or low fetal head can change head shape, this measurement helps describe shape of head

Ratio of BPD/OFD

0.7-0.85 WNL

Dolichocephaly

CI <0.7

Elongated head, BPD shortened

Seen with breech fetuses, holoprosencephaly and oligohydramnios

Brachycephaly

CI >.85

Rounded head, BPD elongated more equal to OFD

More commonly a normal variant than an abnormality

When abnormal can be associated with Trisomy 21

Lateral ventricles measurement

<10mm

Lateral ventricles are best visualized when the ventricular walls are perpendicular to the US beam

Cerebellum grows __mm a week and measures same distance in millimeters and number of weeks GA + or - 3-5mm

1

CM normal measurement

<10mm

Nuchal translucency

Inner to inner in sagittal plane

<3mm 11-14 weeks

Used for chromosomal abnormalities

Nuchal skin fold

Increase in skin thickness of posterior neck

Measured at base of skull in transverse with CSP, cerebellum, CM, and 3rd vent im image

Normal <6mm at 15-21 weeks

Least accurate fetal measurement for dating

AC

AC is more useful for estimating _______ than fetal age

Fetal weight

Hepatic length

Important to r/o hepatomegaly when intrauterine infection is present

Renal length

Important for comparison of size and normal size for fetal age

The femoral diaphysis length can be reliably used after __weeks GA

14

____ transducers provide most accurate measurement of long bones if fetal presentation allows good window

Linear

The middle phalanx of the __th digit is measured when Trisomy 21 is suspected

5

Normal HC/AC ratio

0.87 to 1.33

Normal BPD/FL range

71-87%

FL/AC normal range

20-24%

Normal CI range

70-85%

HC is more accurate for fetal dating than ____

BPD

Higher HC/AC and FL/AC ratios can indicate …

Asymmetric IUGR

Low CI values =

Dolichocephaly

High CI values =

Brachycephaly

Orbital diameter

Trans/axial view of head

Measure outer to outer orbits - Binocular distance

Helpful for dating fetus with abnormal or missing cranium

Lens of eye

Best evaluated in coronal in second tri

Fetal cataracts can be diagnosed as early as __ weeks

15

Nasal bone

Evaluated in sagittal midline profile

Length measured for level 2 evaluations with concerns for Trisomy 21

Fetal MRI

Evaluates brain tissues and surface, CNS abnormalities, diaphragmatic hernia

Preferred after 22 weeks

Singleton growth charts cannot be used for twins over ___ weeks

30

Which of the following measurements does not vary in accuracy with fetal head shape?

BPD

OFD
HC

All of above

HC

Cranial molding

Oligohydramnios or a low fetal head position can lead to external uterine pressure on the head and cause a change in head shape

Brachycephaly is defined as a cephalic index value of ___ and is most commonly considered __________

>0.85; a normal variant

Which of the following is most likely to cause overestimated measurements of the nuchal fold

Including the skin thickness in the measurement

Posterior neck flexion

Scanning the fetus when they are lying face down

Obtaining the measurement after 18 weeks gestation

Posterior neck flexion

All the following should be demonstrated on a correctly obtained image for abdominal circumference assessment, except:

Stomach and portal vein

Abdominal cord insertion

Three ossification centers of vertebral body

A full rib on each side of abdomen

Abdominal cord insert

Higher BPD/FL ratios can indicate:

Trisomy 21 or achondroplasia