THIRD TRIMESTER U/S

MAGDY ABDELRAHMAN MOHAMED

Lecturer of OB/GYN2015

Cardiac activity.Fetal presentation & lie.Fetal size (biometry & estimation

of fetal weight).Fetal anatomy.AF assessment.Placental localization.Evaluation of adnexa.

Fetal biometryBiparietal diameter (BPD).Head Circumference (HC).Abdominal Circumference (AC).Femur length (FL).

BPDLateral ventricle view.Thalami view.

BPDLateral ventricle view.

a rugby-football-shaped skull.Long midline.The cavum septum pellucidum

bissecting the midline one-third of the distance from the synciput to the occiput.

The two anterior horns of the lateral ventricles.

BPDThalami view.

a rugby-football-shaped skull.Short midline.The cavum septum pellucidum

bissecting the midline one-third of the distance from the synciput to the occiput.

the two thalami.

How to measure BPD

Outer to inner technique.

Fetal biometryBiparietal diameter (BPD).Head Circumference (HC).Abdominal Circumference (AC).Femur length (FL).

HC

HC

BPD in breech & transverse lie.BPD measurements can be unreliable.

The fetal head might be dolichocephalic (long and narrow) in shape which lead to underestimation of gestational age.

The head circumference measurement is unaltered by presentation and is therefore a reliable indicator of gestational age.

Fetal biometryBiparietal diameter (BPD).Head Circumference (HC).Abdominal Circumference (AC).

Femur length (FL).

AC Circular transverse section of the

fetal abdomen at the level of the liver.

Visualizing the whole circumference.

Short section of the of the intra hepatic umbilical vein -one third from the anterior abdominal wall.

ACStomach.Spine and descending Aorta.Short ‘unbroken’ rib echo.Ideally spine at 9 or 3 O’clock position.

Wrong?

Fetal biometryBiparietal diameter (BPD).Head Circumference (HC).Abdominal Circumference (AC).Femur length (FL).

FLThe femur should be imaged lying as

close as possible to the horizontal planeCare should be taken to ensure that the

full length of the bone is visualized and the view is not obscured by shadowing from adjacent bony parts.

a single measurement is adequate.

FL

Dating.U/S in 3rd trimester is not accurate

as regard dating ± 3 weak.BPD & HC are better than AC & FL

as regard dating.

Fetal weight.Estimated fetal weight is more

critical in 3rd trimester to detect IUGR & macrosomia.

AC is best marker for fetal weight.

Amniotic fluid assessmentSubjective assessment.Largest vertical pocket (2-8 cm).Amniotic fluid index (AFI).

4 quadrants.Normal 10-15 cm.Oligohydramnious < 5 cm.Polyhydramnious > 25 cm.

Placental localization

Placenta previa1st degree < 5cm from internal

os.2nd degree partially cover internal

os.3rd & 4th degree completely cover

internal os.

Placenta previaRisks factors:

Previous CS.High parity.Multiple pregnancy.Smoking.

Ultrasound Tips? esp. in obese. Fill maternal bladder to push fetus higher

up abdomen.Use umbilicus as acoustic window.Periumbilical area.Suprapubic area.Roll patient into decubitus position and

scan from flank or groin.Transvaginal scan with external

manipulation of the fetus.