OB

• First trimester

  • CRL is accurate for estimation of gestational age (+/- 1 wk)

  • Decidual cyst may represent early breakdown of the decidua

• Second trimester

  • 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

• Ectopic pregnancy

  • 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.

• Growth

  • SGA

    • 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.

  • Symmetric IUGR

    • 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.

• Umbilical vessels

  • Two umbilical arteries

    • A/B (peak systolic to end diastolic ratio) provides assesment of resistance to flow.

• BPP (0-10)

  • Assess acute hypoxia

    • HR - nonstress test

    • Breathing

    • Gross body movement

    • Overall tone

  • Assess chronic hypoxia

    • Amniotic fluid

• Polyhydramnios

  • Associated with CNS and GI anomalies

  • Mesoblastic nephroma and fetal ovarian cyst are also associated

• CNS

  • Anencephaly

    • Polyhydramnious is a secondary finding

  • Hydrocephalus

    • Ventriculomegaly and enlarged head

    • Thin parenchymal mantle is present

  • Hydranencaphaly

    • No cortical mantle

  • Microcephaly

    • TORCH

  • Holoprosencephaly

  • Facial clefts

  • Cephalocele/Encephalocele

  • Posterior fossa

    • 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.

  • Triple screen

    • 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

  • Meningocele/myelomenigocele

  • Paraspinal abnormalities

    • 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

• Chest

  • Cystic chest masses

    • Congenital diaphragmatic hernias

    • Type I and type II CAM

    • Bronchogenic cysts

    • Duplication cysts

    • Pulmonary sequestration

  • Solid chest lesions

    • Congenital diaphragmatic hernias

    • Type III CAM

    • Bronchopulmanory sequestration

  • Enlarged hyperechoic lungs

    • Laryngeal atresia

  • Aortic enlargement with small pulmonary artery

    • TOF

    • Hypoplastic right heart

  • VSD

    • Four types:

      • Perimembranous

      • Muscular

      • AV canal

      • Supracristal

    • 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

• Abdomen

  • Pseudoascites => does not extend deep to the ribs

  • Umbilical vein varix

  • Esophageal atresia

    • Polyhydramios and absent stomach bubble

  • Duodenal atresia

    • Double-bubble sign

  • Meconium ileus

  • Meconium peritonitis

  • Hyperechoic bowel

    • Cystic fibrosis

    • CMV

    • Chromosomal abnormalities

  • Anterior abdominal wall defects

    • Omphalocele => associated with other abnormalities

    • Gastrochisis

      • Umbilical cord inserts normally

      • Not covered by the membrane

    • Pentalogy of Cantrell

      • Ectopia cordis

      • Omphalocele

      • Diaphragmatic defect

      • Pericardial defect

      • Disruption of sternum

    • Limb-body wall complex

      • Deformities from amniotic bands

• GU

  • Bilateral hydronephrosis

    • Posterior urethral valves

    • Cloacal or urethral atresia

  • Unilateral obstruction

    • Multicystic dysplastic kidney

    • UPJ obstruction

  • Urinary bladder should be seen not later than 16 weeks.

• Skeletal

  • Thanatophoric dwarfism (most common lethal dysplasia)

    • Hydrocephalus, cloverleaf skull

    • Polyhydramnios

    • Severe micromelia

  • Homozygous achondroplasia

    • Severe micromelia

  • Heterozygous achondroplasia

    • Rhizomelia

  • Osteogenesis imperfecta

    • Osteoporosis

    • Micromelia, bone bowing, fractures

• Placenta

  • Normal thickness < 5cm

  • Subchorionic or retroplacental hemorrhages

  • Placenta accreta (invasion to myometrium), increata (invasion into myometrium), percreta (invasion through myometrium)

  • Placenta previa

  • Hydropic placental changes

    • DiffDx: Hydatiform mole

  • Placental infarcts

    • Usually not significant unless involve > 50% of the placenta

  • Chorioangioma

    • Benign placental vascular neoplasm

• Umbilical cord

  • 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

• Cervical incompetence

  • Normal length = 4cm

  • Incompetent cervix < or = 2.5 cm

    • Funneling of the endocervical canal can be seen

• Hydatiform moles

  • Complete

    • Non-invasive in 85% of cases

    • Locally invasive (chorioadenoma destruens) 13%

    • Invasive (choriocarcinoma) 2%

  • Partial

  • Theca lutein cysts can be seen

• Twin pregnancy

  • Risk of complications increases from single pregnancy to twin dichorionic diamniotic to mochorionic monoamniotic

  • Embryology

    • 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.

• Syndromes

  • Down syndrome

    • Most common chromosomal abnormality

    • Nuchal translucency > 3 mm in the first trimester or > 6 mm between 16 to 22 weeks.

    • Short humerus and femur

    • Echogenic bowel

    • Cystic hygroma

    • Duodenal atresia

    • Hydrocephalus

    • AV canal defects/TOF

Twin twin transfusion syndrome staging

• Stage 1

  • Polyhydramnious in recipient, oligohydramnious in donor

• Stage 2

  • Absent bladder in donor

• Stage 3

  • Abnormal cardiovascular function in either twin

• Stage 4

  • Heart failure in either twin

• Stage 5

  • Fetal demise in either twin