CRL is accurate for estimation of gestational age (+/- 1 wk)
Decidual cyst may represent early breakdown of the decidua
BPD is accurate for estimation of gestational age (+/- 1 wk)
Normal gestational sac
Double decidual sign
Two hyperechoic lines, which surround a hypoechoic closed endometrial canal
Continous hyperechoic rim of 2 mm in thickness or greater
Spherical or ovoid shape
Growth of 1.2 mm/day
Pseudogestational sac occurs in 5%
Ectopic embryo with heart motion (PPV = 100%)
Adnexal mass with yolk sac or nonliving embryo (PPV almost 100%)
Tubal ring (PPV = 92%)
Adnexal mass (PPV = 95%)
Moderate to large amount of free fluid especially with internal echoes.
Can be constitutionally small or growth restricted
Asymmetric IUGR is a form of starvation with loss of subcutaneous fat and liver glycogen stores, which lead to decrease in abdominal size.
Asymmetric IUGR is usually seen in the third trimester.
Usually results from maternal and placental problems.
Volume of amniotic fluid may be decreased.
Usually occurs in the first trimester from insult to fetus or mother
Volume of amniotic fluid is normal
Macrosomia (4000-4500 gm or >90%)
Shoulder dystocia, particularly if asymmetrically large.
Two umbilical arteries
A/B (peak systolic to end diastolic ratio) provides assesment of resistance to flow.
Assess acute hypoxia
HR – nonstress test
Gross body movement
Assess chronic hypoxia
Associated with CNS and GI anomalies
Mesoblastic nephroma and fetal ovarian cyst are also associated
Polyhydramnious is a secondary finding
Ventriculomegaly and enlarged head
Thin parenchymal mantle is present
No cortical mantle
Cisterna magna obliterated => Chiari II
Lemon sign => flattening of frontal bones
Banana sign => abnormal curved shape of the cerebellum
Cisterna magna is large => Dandy-Walker
Diff. Dx. => Megacisterna magna, arachnoid cyst
Nuchal fold measured in AP at 15-21 weeks => layer of soft tissue posterior to occipital bone
Most sensitive and specific US marker for trisomy 21.
Nuchal translucency measured in sagittal plane at 11- 14 weeks => hypoehoic region along the posterior portion of fetal neck
Marker for aneuploidy (trisomy 21, trisomy 18, trisomy 13, Turner’s syndrome)
Choroid plexus cysts
If no other abnormalities to suggest trisomy 18 (clenched fist with overlapping fingers, rockerbottom feet deformity, cardiac anomalies) are present, choroid plexus cyst may be a normal variant.
AFP, hCG, unconjugated estriol
Trisomy 21 => low, high, low
Trisomy 18 => all three are low
Strawberry sign => banana sign due to hypoplasia of the frontal lobes and flattened occiput from hypoplasia of the hindbrain
Agenesis of corpus callosum
Vein of Galen aneurysm
May cause obstruction of the aqueduct of Sylvius
Cervical => cystic hygromas
Have spoke-wheel appearance
Lumbar => teratomas, which can be completely internal or external
Differential of posterior neck mass
Cephalocele => presents with calvarial defect
Cystic hygroma => demonstrates spoke-wheel appearance
Teratoma => contains solid, fluid and calcified components
Cervical meningocele => associated with spinal defect
Cystic chest masses
Congenital diaphragmatic hernias
Type I and type II CAM
Solid chest lesions
Congenital diaphragmatic hernias
Type III CAM
Enlarged hyperechoic lungs
Aortic enlargement with small pulmonary artery
Hypoplastic right heart
Other cardiac anomalies are seen on 40% of cases
Intracardiac hyperechoic focus
Calcification of papillary muscle
Intracardiac hyperechoic focus is seen in 17% of aneuploid fetuses
The significance of this finding in general population is controversial
Pseudoascites => does not extend deep to the ribs
Umbilical vein varix
Polyhydramios and absent stomach bubble
Anterior abdominal wall defects
Omphalocele => associated with other abnormalities
Umbilical cord inserts normally
Not covered by the membrane
Pentalogy of Cantrell
Disruption of sternum
Limb-body wall complex
Deformities from amniotic bands
Posterior urethral valves
Cloacal or urethral atresia
Multicystic dysplastic kidney
Urinary bladder should be seen not later than 16 weeks.
Thanatophoric dwarfism (most common lethal dysplasia)
Hydrocephalus, cloverleaf skull
Micromelia, bone bowing, fractures
Normal thickness < 5cm
Subchorionic or retroplacental hemorrhages
Placenta accreta (invasion to myometrium), increata (invasion into myometrium), percreta (invasion through myometrium)
Hydropic placental changes
DiffDx: Hydatiform mole
Usually not significant unless involve > 50% of the placenta
Benign placental vascular neoplasm
Increased incidence of anomalies in two vessel cord
Velamentous cord insertion => insertion site located beyond margin of placenta
Vasa previa => fetal vessels cross internal os
Normal length = 4cm
Incompetent cervix < or = 2.5 cm
Funneling of the endocervical canal can be seen
Non-invasive in 85% of cases
Locally invasive (chorioadenoma destruens) 13%
Invasive (choriocarcinoma) 2%
Theca lutein cysts can be seen
Risk of complications increases from single pregnancy to twin dichorionic diamniotic to mochorionic monoamniotic
Dichorionic diamniotic=> two separate ova and sperms or very early division of blastomere
Monochorionic diamniotic (1-7 days) => common chorion but separate amniotic sacs. Placental circulation may be parially or completely shared.
Monochorionic monoamniotic (7-13 days) => common chorion and common amnion
Conjoint twins (after 13 days) => embryos fail to completely separate
Number of placentas and sex
Two placentas define dichorionic diamniotic pregnancy
One placenta may be two separate placentas of dichorionic pregnancy or fused placenta of the monochorionic pregnancy
Evaluation of the genitalia is possible during mid second trimester (if different sexes than the pregnancy is dichorionic diamniotic
Lambda sign (twin peaks or triangle)
Placenta extends between sacs
Useful when only one placenta is identified. If seen in the second or third trimester, Lambda sign accuratelly predicts dichorionic diamniotic pregnancy.
Type of interposed membranes.
Four layers in the diamniotic dichorionic pregnancy are well defined and measure at least 2mm in thickness.
Monochorionic diamniotic membrane is thin (1mm) because it is composed of two thin layers of amnion
No interposed membrane in monochorionic monoamniotic pregnancy
Well defined thick memrane is diagnositic of dichorionic diamniotic pregnancy in all trimesters.
Late in pregnancy dichorionic diamniotic membrane may be thinned.
Most common chromosomal abnormality
Nuchal translucency > 3 mm in the first trimester or > 6 mm between 16 to 22 weeks.
Short humerus and femur
AV canal defects/TOF
Twin twin transfusion syndrome staging
Polyhydramnious in recipient, oligohydramnious in donor
Absent bladder in donor
Abnormal cardiovascular function in either twin
Heart failure in either twin
Fetal demise in either twin