Obstetrical Ultrasound

Obstetrical Ultrasound

By La Lura White M.D.Maternal Fetal Medicine

Obstetrical Ultrasound• Introduced in the late 1950’s

ultrasonography is a safe, non-invasive, accurate and cost-effective means to investigate the fetus

• Computer generated system that uses sound waves integrated through real time scanners placed in contact with a gel medium to the maternal abdomen

• The information from different reflections are reconstructed to provide a continuous picture of the moving fetus on the monitor screen

Obstetrical Ultrasound• Indications:• Unsure last menstrual period• Vaginal bleeding during pregnancy• Uterine size not equal to expected for dates• Use of ovulation-inducing drugs confirm early pregnancy• Obstetric complications in a prior pregnancy: ectopic, preterm

delivery• Screen for fetal anomaly: abnormal serum screens, certain drug

exposure in early pregnancy, maternal diabetes. Rh isoimmunization

• Postdate fetus• Twins (monochorionic)• Intrauterine growth restriction (IUGR)

RADIUS study (1993) did not support routine US screening

Obstetrical Ultrasound• 1st. Trimester (less than 12 weeks)• Gestational sac location / size / shape• Embryo• Yolk sac• Amnion• Fetal cardiac activity• Placental position/Umbilical cord• Amnionitic fluid• Fetal morphology >11 weeks)• Cranium• Heart• Stomach/Bladder/Cord insertion/presence of limbs, hands

and feet


• Pre and peri-ovulation (1-2 weeks): ovarian follicle matures and ovulation

• Conceptus (3-5 weeks): Corpus luteum, fertilization, morula, blastocyst, bilaminar embryo

• Embryonic (6-10 weeks): Trilaminar C-shaped embryo

• Fetal Phase: (11-12 weeks):

Obstetrical Ultrasound (TVU)

Gestational sac: seen at 4 weeks, fluid filled with echogenic border, grow at least 0.6 mm daily.15

Yolk sac: 33 days (4.7 wk)

Embryonic echoes: 38 days (5.4 w) with embryo at 6 wk

In a normal pregnancy, the embryo should be visible if the gestational sac is 25 mm or larger in diameter.

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• An intrauterine gestational sac should be visualized by transvaginal ultrasound with β-hCG values between 1000 and 2000 IU and abdominal exam 5500-6500 IU

• Visible heart activity: 43 days (6.1w)• Normal heart rate at 6 weeks: 90-110 bpm • At 9 weeks:140-170 bpm.• At 8-9 weeks if nl heartbeat: no bleeding 3%loss

bleeding 13% loss• At 5-8 weeks a bradycardia (<90 bpm) is associated with a

high risk of miscarriage.


• CRL(Crown Rump Length):• Longest length excluding

limbs and yolk sac• Made between 7 to 13 weeks• 3 days: 7-10 weeks• 5 days: 10-14 weeks• Fetal CRL in centimeters plus

6.5 equals gestational age in weeks

Obstetrical Ultrasound• Ultrasound findings in a

pregnancy destined to abort include:

• A poorly-defined, irregular gestational sac

• A large yolk sac (6 mm or greater in size)

• Low site of sac location in the uterus

• Empty gestational sac at 8 weeks' gestational age (the blighted ovum).

Obstetrical Ultrasound• First Trimester Screening• In 2007, the American College of Ob Gyn endorsed offering

aneuploidy screening to all gravidas• Performed between 11 and 13 weeks 6 days (fetal crown–rump

length 42–79 mm).• Fetal nuchal translucency and maternal blood, β-hCG and

pregnancy-associated plasma protein A (PAPP-A). • This test can detect approximately 60-85% of fetuses with

Down syndrome, with a 5% false positive rate.2• Abnormal screen can increase the risk of genetic, other

aneuploidies and other cardiac anomalies

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Obstetrical Ultrasound• Nuchal translucency:• Translucent space between the back of the

neck and the overlying skin• The scan is obtained with the fetus in sagittal

section and a neutral position .• The fetal head (neither hyperflexed nor

extended, either of which can influence the nuchal translucency thickness).

• The fetal image is enlarged to fill 75% of the screen, and the maximum thickness is measured, from leading edge to leading edge. (inner to inner measurement)

• It is important to distinguish the nuchal lucency from the underlying amnionic membrane.

• > 6 mm considered abnormal

Obstetrical Ultrasound• 2nd Trimester Ultrasound (13 weeks-24 weeks)• Fetal survey:• Fetal number• Viability• Presentation• Fetal biometry

• Amnionitic fluid• Placenta• Cervix • Fetal Anatomic screening

Obstetrical Ultrasound• Cervical length• Endovaginal probe, examine in dorsal lithotomy position

with empty bladder• Normal cervix should have a length of 2.5cm or more from

10 weeks gestation until 36 week• The width of the cervical canal at the level of the internal

os should be less than 4mm• Document any evidence of funneling• Optimal gestational age for cervical length assessment is

after 16 to 20 weeks gestation• Assessment 20-24 weeks best time evaluation PTD


• Transvaginal probe

• Full bladder

• Cervical Length: internal os to external os


• Funneling (percentage): internal os to end of funneling over total cervical length)

Obstetrical Ultrasound• BPD:• Greatest accuracy between 12-28 weeks

(better>14 wks.)• The plane for measurement of head circumference

(HC) and bi-parietal diameter (BPD)must include:• Cavum septum pellucidum• Thalamus• Choroid plexus in the atrium of the lateral

ventricles.• Measure outer table of the proximal skull to the

inner table of the distal

• HC:• Measure the longest AP length• (BPD + OFD) X 1.62

Obstetrical Ultrasound• Abdominal circumference

• Determined on transverse view at the level of the junction of the umbilical vein, portal sinus, and fetal stomach

• Measured from the outer diameter to outer diameter

• Multiply mean diameter by 3.14

• Assessing fetal weight/IUGR/macrosomia

Obstetrical Ultrasound• Femur Length (FL):• Aligning the transducer with the lower

end of the fetal spine and rotating toward the ventral aspect of the fetus

• Can measure from 10 weeks onward• Measurement origin to distal end of

shaft and shows two blunted ends• Do not include femoral head or distal

epiphysis• Femur image is at an angle of less than

30 degrees to the horizontal.• It increases from about 1.5 cm at 14

weeks to about 7.8 cm at term.• Humerus• Measured similarly

Obstetrical Ultrasound• Amnionitic Fluid• AFI: measure four quadrants

of largest verticle pocket• 5-20 cm. nl, 6-8 cm.

borderline, <5 cm oligohydramnios

• Polyhydramnios is defined as an amniotic fluid volume in excess of 2000 mL. A single pocket of fluid that is 8 cm or larger

Obstetrical Ultrasound• Placenta:• Determining its upper and lower edges r/o

placenta previa• With increasing gestational age, the placenta

increases in echogenicity because of increased fibrosis and calcium content.

• This feature of placental maturation has led to a grading of placentas from immature (grade 0) to mature (grade 3).

• Placentolmegaly

Diabetes, fetal hydrops, Rh isoimmunization

• Small placenta:• Severe IUGR (symmetrical/asymmetrical)

Grade 0

Grade 1

Grade 3

Obstetrical Ultrasound• Abnormal placentas• Placenta Previa• found in approximately 5% of

second-trimester scans• If detected at 15–19 weeks, it

persists in 12% of patients.• If it is detected at 24–27

weeks, it may persist in up to 50%.

• Vasa Previa: membranous insertion of cord where exposed vessels cross internal os


• Fetal anatomy: • Head

• Atrium of lateral ventricles• Choroid plexus assessment• Cerebellum • Cisterna magna• Nuchal fold

Obstetrical Ultrasound• The atrium of lateral

ventricles should be less than 10mm in diameter (best measured at the occipital horn).

• The choroid plexii should be homogenous.

• Small, and sometimes multiple, choroid plexus cysts are a common finding on high resolution equipment.

• They are of doubtful significance as an isolated finding.


The cerebellar diameter should approximately equal the weeks of gestation. (Ex: 19weeks=19mm)Cisterna magna: < 10mmNuchal fold: (outer edge of occipital bone to skin surface ) <6mm (between 17-20weeks).

• Face:• Profile• Nasal

bone

• Nose• Lips


• Thorax • Lung volumes• Diaphphram• r/o CCAM• Congenital

diaphragmatic hernia

Obstetrical Ultrasound• Fetal Circulation• Blood from the placenta is carried to the fetus by the

umbilical vein• About half of this enters the fetal ductus venosus and is

carried to the inferior vena cava• The other half enters the liver proper from the inferior

border of the liver. • The branch of the umbilical vein that supplies the right

lobe of the liver first joins with the portal vein. • The blood then moves to the right atrium of the heart. • In the fetus, there is an opening between the right and

left atrium (the foramen ovale), and most of the blood flows through this hole directly into the left atrium from the right atrium, thus bypassing pulmonary circulation.

• The continuation of this blood flow is into the left ventricle, and from there it is pumped through the aorta into the body

Obstetrical Ultrasound– Some of the blood entering the

right atrium does not pass directly to the left atrium through the foramen ovale, but enters the right ventricle and is pumped into the pulmonary artery.

– In the fetus, there is a connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs

Obstetrical Ultrasound• Cardiac Anatomy• Four-Chamber View of the Heart

• The ultrasound beam is directed perpendicular to the midchest plane at the level of the heart.

• These chambers consist of the right and left atrial and both ventricular chambers

• Corresponding valves between them

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• The heart is approximately one-third the area of the chest, inclined to the left 45 degrees to the midline.

• The AP midline passes through the left atrium and the right ventricle

• The midline (AP) and the cardiac axis (arrowhead on dashed line) intersect and form the angle shown

• Look for asymmetry in chamber size, defects in the septum or displacement of the heart

• Detection rate 60-75% for anomalies with 4 chamber view, higher with outflow tracts

Obstetrical Ultrasound• Sweep the transducer beam in a transverse plane from the level

of the four chamber view towards the fetal neck• Right Outflow Tract Left Outflow Tract• Right outflow track comes Comes off left ventricle off right ventricle and bifurcates continues into aortic arch continues into pulmonary artery and then to descending

aorta


• Detect Fetal Heart Rate• M-mode

Obstetrical Ultrasound• Abdomen /Stomach (presence, size, and

situs)

• Liver

• Cord Insertion:• Ensure the abdominal wall

around the cord insertion is intact

• No bowel has herniated into the cord.

• 3-vessel


• Kidneys/Bladder• Kidneys• Confirm the presence

and position of both kidneys.

• Look for the anechoic renal pelvis.

• The renal pelvis TS diameter should be less than 5mm.

Obstetrical Ultrasound• Abnormal• Renal:• urethral atresia: large fetal

bladder (bl), urinary ascites (asc), and hydronephrotic kidneys

• Posterior urethral valves with keyhole bladder


• Spine:• Coronal or Sagital

of entire spine:• cervical• Thoracic• Lumbar• Sacral

• Transverse assessment of entire spine

Obstetrical UltrasoundUpper ExtremitiesNormal

Abnormal

Fist clenched Phocomelia

Obstetrical Ultrasound• Lower Extremities:


• Abnormal Ultrasounds

• Omphalocele

• Gastrochesis


• Doppler Ultrasound• Blood flow characteristics in the fetal blood vessels can be assessed

with Doppler 'flow velocity waveforms‘• Diminished flow, particularly in the diastolic phase of a pulse cycle is

associated with compromise in the fetus. • Various ratios of the systolic to diastolic flow are used as a measure of

this compromise. • The blood vessels commonly interrogated include the umbilical artery,

the aorta, the middle cerebral artery, ductus venosus (DV) and umbilical vein (UV)

• Abnormal uterine artery Doppler velocimetry and pre-eclampsia, intra-uterine growth retardation and adverse pregnancy outcomes.

Doppler Ultrasound

• Ductus venosus leads directly into the vena cava to allows some blood rich in oxygen and nutrients to be pumped out of the body without passing through the capillary beds in the kidney.

• Abnormal waveforms in the ductus venosus may be key to predicting right heart failure in the hypoxic fetus and an important indicator of imminent fetal demise (Kiserud 1991).

• Reversed flow in the ductus venosus is an ominous sign.

Doppler Ultrasound• The umbilical artery is

evaluated measuring the blood flow velocity at peak systole (maximal contraction of the heart) and peak diastole (maximal relaxation of the heart)

• These values are computed into different ratios like S/D or RI

Doppler Ultrasound

• Predict fetuses at risk for anemia or hydrops especially Rh alloimmunized pregnancies

• >1.5 MOM or ratios can be used

Obstetrical Ultrasound• Three-Dimensional

Ultrasound3D• Display multiple longitudinal,

transverse, and coronal images.

• Images may improve the accuracy of anomaly detection of the fetal face, ears, and distal extremities


• Abnormal 3D Images

Cleft lip Cyclopia


• 4D Ultrasounds that adds the element of time to the 3D process.

• Offers live images• Fetal changes like movement, kicking, reach

with hands and facial expressions can be seen


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Obstetrical Ultrasound

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