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  • 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