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24October2014

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Basic OB Ultrasound

Basic OB Ultrasound

Preface

Why Ultrasound?

Appropriate use is helpful in obstetric practice, especially in gestational age estimation, fetal growth monitoring, obstetric hemorrhage, and anomaly screening

Indicated or Routine Ultrasound?

  • Generally well accepted for examination with indication
  • Routine screening at 18-20 weeks, recent more common practice, better or earlier diagnosis of GA, twins or anomaly but significant increase in cost and workload
  • The policy must be considered for cost-effectiveness and cost-benefit

Common Indications

  1. Diagnosis: pregnancy, number of fetuses, fetal life
  2. Size inconsistent with date: multiple pregnancy, oligo-, polyhydramnios, hydrocephalus, fetal growth restriction
  3. Estimate gestational age
  4. Growth monitoring
  5. Bleeding: abortion, placenta previa, placental abrutpion
  6. Amniotic fluid evaluation
  7. Pathology in the pelvis
  8. Anomaly screening: Routine at 18-20 wk or pregnancy at risk (maternal DM, familial history,advanced maternal age)
  9. Guidance for invasive procedures, i.e. amniocentesis, cordocentesis

 

Sonoembryology

Sonoembryology

Early Fetal Development

(Transvaginal Sonography; TVS)

  • 3-4 weeks (after LMP): Endometrial thickenings
  • 4-5 weeks: Gestational sac
  • 5-6 weeks: Yolk sac, double decidual sac sign (DDS)
  • 6-7 weeks: Embryo with heart beat
  • 7-8 weeks: Embryo movement, Rhombencephalon, Amnion
  • 8-9 weeks: Physiologic omphalocele, limbs, choroid plexus, spinal line
  • TVS demonstrates earlier than transabdomen (TAS) ~ 1-2 weeks

 

4-5 weeks

Endometrial thickening, no obvious sac

5 weeks

Gestational ring, white echogenic rim

Double decidual sac sign

Usually seen at 5-6 weeks

5 weeks

Note yok sac

6 weeks

Note: yok sac and early embryo

7-8 weeks

Rapid growth of embryo and amnion

8 weeks

Fetal body compartments : head trunk limbs

10 weeks

Facial structures becoming seen

Double Decidual Sac Sign (DDS)

  • Strongly suggestive of intrauterine pregnancy
  • Outer ring : Decidual vera
  • Middle sonolucency : Endometrial cavity
  • Inner ring : Decidual capsularis
  • Typically seen : 5-8 weeks

Double decidual sac sign

Usually seen at 5-6 weeks

5 weeks

Note yok sac

Mean Sac Diameter (MSD)

  • MSD : Average gestational sac diameter = width + depth + length / 3
  • MSD closely related to early GA
  • When MSD > 25 mm. GA (days) = MSD + 30

Mean sac diameter

Longitudinal diameter

Mean sac diameter

Transverse diameter and depth

 

Yolk Sac

  • Round, sonolucent with white border
  • Average 5 mm (3-8 mm)
  • Seen at 6-12 weeks peak 8-10 weeks
  • Nearly all seen when MSD > 8 mm.
  • Yolk sac > 10 mm. related to poor prognosis
  • Must be seen if MSD > 20 mm. by TAS or > 13 mm by TVS

Fetal Echo

  • Crown-Rump Length (CRL): the most accurate parameter for GA estimation (+ 3-7 days)
  • Useful only in the first trimester
  • Short CRL related to high abortion rate and aneuploidy
  • Head, trunk, limbs can be identified from 8 weeks

Amnion

  • Seen from 7-8 weeks (TVS)
  • Beginning with double bleb sign (yolk sac and amnionic sac)
  • Fast growing, finally embryo is in the sac
  • Yolk sac is outside

Yolk sac

Yolk sac adjacent to fetal echo in early gestation

Yolk sac

Note: yolk sac separated from amnion

 

 

Physiologic Omphalocele

  • Midgut herniation 8-12 weeks
  • Only bowel (no liver) in the proximal umbilical cord
  • Not seen if CRL > 44 mm
  • Size 4-7 mm.
  • Should be considered abnormal if > 7 mm, or seen after 12 weeks

Physiologic omphalocele

Prominent at 8-9 weeks

Physiologic omphalocele

At 8 weeks

 

Physiologic omphalocele

Physiologic omphalocele in abortus

 

Nuchal Translucency (NT)

  • NT : small fluid collection beneath skin at back of the fetal neck
  • Measured at CRL 35-80 mm (10-14 week)
  • Measured on midsagittal scan (plane for CRL)
  • The best sonomarker for screening Down syndrome
  • Abnormal if > 95th percentile (> 2.5-3.0 mm)
  • Thickened NT increased of aneuploidy, anomaly especially cardiac defect

Nuchal translucency

Normal measured at 11 weeks

Nuchal translucency

Thickened nuchal translucency

Nuchal translucency

Thickened nuchal translucency at 14 weeks

Nuchal translucency

Thickened nuchal translucency after abortion

Early Complications

Early Pregnancy Complications

Threatened Abortion

  • Ultrasound examinations see if viable or nonviable pregnancy
  • Viable fetus with normal heart beat : very good prognosis
  • Nonviable:
    • blighted ovum
    • missed / incomplete abortion
    • fetal death
    • ectopic pregnancy
    • molar pregnancy

 

Threatened abortion

Normal fetus at 11 weeks

Threatened abortion

Placental hematoma in case of blighted ovum

 

Early embryo death

Embryo size and sac disproportion

 

Blighted Ovum (Empty sac)

  • Intrauterine pregnancy without embryo
  • Diagnosed when
  • MSD > 25 mm (TAS) or > 20 mm (TVS) with no embryo seen
  • MSD > 20 mm (TAS) or >17 mm (TVS) with no yolk sac & embryo seen
  • DDx :
  • Early normal pregancy
  • Pseudosac in ectopic pregnancy
  • Blood or fluid collection

Blighted ovum

Gestational sac without embryo, subcorion hematoma

Blighted ovum

Gestational sac without embryo,

 

Blighted ovum

Aborted sac: placenta and sac without embryo

 

Ectopic Pregnancy

  • Clinically suspected with stable vital sign : ultrasound
  • Ultrasound results:
  • Definite IUP : exclude ectopic pregnancy
  • Definite EUP : extrauterine gestational sac
  • Highly suggestive of EUP : empty uterus with complex mass (separate from ovaries), echogenic fluid, dilated tube (May treat EUP or laparoscopic diagnsois in some cases)
  • Inconclusive : empty uterus without other abnormal finding (May need doubling time for beta-hCG)

    Ectopic pregnancy

    Floating dilated fallopian tube in free fluid

    Ectopic pregnancy

    Gestational sac with embryo and yolk sac in the tube

     

    Ectopic pregnancy

    Adnexal omplex mass of blood clot and concepitus

     

     

    Molar Pregnancy

    • Ultrasound findings:
    • No fetus
    • Snow storm pattern or
    • Numerous small cystic echo or
    • Placental-like echo
    • May show complex area of blood clot

     

    Molar pregnancy

    Numerous small cystic space in uterine cavity mass

    Molar pregnancy

    Snow storm appearance

     

    Molar pregnancy

    The opened uterine specimen after hysterectomy

     

     

     

Biometry

Fetal Biometry

Mean Sac Diameter (MSD)

  • MSD : Average gestational sac diameter = width + depth + length / 3
  • MSD closely related to early GA
  • When MSD > 25 mm. GA (days) = MSD + 30

Mean sac diameter

Longitudinal diameter

Mean sac diameter

Transverse diameter and depth

Crown-Rump Length (CRL)

  • The most accurate parameter for GA (+ 3-7 days)
  • Most accurate during 6.5-10 weeks
  • Limitation: Appropriate only in first trimester
  • Technique:
  • Mid-sagittal scan (note fetal nose, spine, crown and rump)
  • Measurement from the topmost of head to rump end
  • Precaution: best done in neutral position, not include yolk sac or limbs

 

Crown-rump length

8 weeks

Crown-rump length

9 weeks

 

Crown-rump length

12 weeks

 

Biparietal Diameter (BPD)

  • The best parameter during 2nd trimester (+ 7-11 days during 14-26 weeks)
  • Technique: the distance from outer-to-inner skull table in the plane visualized of
  • Ovoid and symmetry
  • Thalamus
  • Midline echo / third ventricle
  • Cavum septum pellucidum
  • Limitation: less reliable in case of
  • Cephalic index (CI: BPD/OFD x 100) < 75% (dolichocephaly) or > 85% (brachycephaly) (normal CI 85%; 75-85%)
  • Irregular skull shape or hydrocephalus
  • Varied in 3rd trimester (+ 2-3 wks)

Head Circumference (HC)

  • Measurement on the same plane as BPD
  • The accuracy similar to BPD (+ 1 wk before 20 wk and + 2-3 wk in the 3rd trimester)
  • Theoretically better than BPD, but practically less accurate due to poor imaging of anterior and posterior of the skull secondary to acoustic shadow

 

Biparietal diameter

Standard plane for BPD measurement

Biparietal diameter

Standard plane for BPD measurement

Dolichocephaly

BPD not proper for gestatational age calculation

Brachycephaly

BPD not proper for gestatational age calculation

 

Abdominal Circumferece (AC)

  • Most varied among the standard parameter
  • Less accurate for GA estimation
  • Best parameter for fetal growth evaluation or estimate fetal weight
  • Plane for AC:
  • as round as possible
  • umbilical vein (middle-third) running to portal sinus in the liver (Note: if umbilical vein seen closely to anterior wall the plane is too low or oblique)
  • stomach
  • Measurement: perimeter around fetal skin
  • Limitation: not accurate for GA, not round due to pressure effect

 

Abdominal circumference

Standard plane for abdominal circumference measurement

Abdominal circumference

Standard plane for abdominal circumference measurement

 

Abdominal circumference

Standard plane for abdominal circumference measurement

 

 

Femur Length (FL)

  • The accuracy for GA similar to BPD, may be slightly less accurate and more accurate than BPD in 2nd and 3rd trimester respectively
  • Plane: the longest plane and straight with least curve as possible
  • Measurement between the both end, not include epiphysis
  • Precaution: FL among Thai is shorter than that of western pregnanc

 

Femur lenght

Standard plane for femur length measurement

Femur lenght

Standard plane for femur length measurement

 

Femur lenght

Standard plane for femur length measurement

 

 

Fetal Growth Restriction (FGR)

  • AC : most commonly used for diagnosis
  • HC/AC ratio : increased in FGR ( the ratio is date dependent ; decreasing with GA, > 1 before 32 week, ~ 1 during 32-36 wk, > 1 after 36 wk) unreliable for symmetrical FGR
  • FL/AC ratio : (date-independent) constant after 20 wk (normal ratio ~22+2 abnormal if > 24), unreliable for symmetrical FGR
  • Umbilical artery Doppler waveforms: high resistance or absent end-diastole for true FGR but normal for constitutional small fetus
  • Oligohydramnios is common among FGR
  • Estimate fetal weight (< 10th percentile)
  • Grade 3 placenta before 36 week

 

Fetal Growth Restriction (FGR)

FGR due to twin-to-twin transfusion syndrome

Fetal Growth Restriction (FGR)

FGR due to twin-to-twin transfusion syndrome

Placenta

Placenta & Amniotic Fluid

Amniotic Fluid

  • Amniotic fluid index (AFI): Sum of the four deepest depth of AF four quadrant
  • Oligohydramnios (AFI < 5) : commonly associated with FGR, rupture of membranes, and anomaly i.e. renal agenesis, polycystic kidney
  • Polyhydramnios (AFI > 95th centile or > 20-25) : commonly related to maternal DM, anomaly i.e.
  • esophageal atresia
  • neural tube defects
  • aneuploidy etc.

 

Amniotic fluid index

Four quadrant deepest verical pocket measurement

Polyhydramnios

Polyhydramnios due to fetal anencephaly

 

Placental grading

  • 0 : no calcifications
  • 1 : scattered calcifications
  • 2 : basal calcifications
  • 3 : basal and septal calcification; outline the cotyledons; commonly seen in postterm, FGR, PIH
  • Extensive calcification < 36 wk related to FGR

     

    Placental Grading

    Placental Grade 0

    Placental Grade 1

    Placental Grade2

     

    Placental Grade 3

     

     

    Placenta Previa

    • Marginal previa : adjacent to the internal os
    • Partial previa: placenta covers a portion of internal os (indistinguishable from marginal previa in prenatal practice)
    • Total previa: placenta covers the os
    • Low-lying placenta: nearly the os, not true previa and vaginal deliver is possible
    • Ultrasound: should be done with an empty bladder because the cervix is spuriously long by full bladder leading to false previa
    • Most placenta previa diagnosed in the 2nd trimester is away from the os at term
    • The cervix could be visualized using TAS, TVS or transperineal approach

     

    Placenta previa totalis

    Standard plane for BPD measurement

    Placenta previa totalis

    Standard plane for BPD measurement

    False placenta previa totalis

    Full bladder compress lower segment, simulating placenta previa totalis

    False placenta previa totalis

    The same case (after voiding)

     

    Placental Abruption

    • cystic, complex, or hypoechoic areas may be seen between placenta and uterine wall
    • Placental thickening
    • reveal type may be not diagnosed
    • retro placental hematoma may be isoechoic like placenta

     

    Placental abruption

    Placental abruption

    Placental abruption

    Placental abruption

     

Fetal Anomaly

Fetal anomaly

Fetal Hydrops

  • Fluid accumulation : subcutaneous edema, ascites, pleural effusion, pericardial effusion, placentomegaly
  • Most due to Hb Bart’s disease (1 : 1000 birth in northern Thailand), usually not related to other anomaly
  • Other causes
  • Rh isoimmunization
  • Fetal anomaly: cystic hygroma, cardiac anomaly, supraventricular tachycardia
  • Aneuploidy: 45XO, Down syndrome
  • Infections: parvovirus B 19, syphilis
  • Miscellaneous: chorioangioma, twin-twin transfusion syndrome etc.

Sonographic Findings of Hb Bart’s disease

  • cardiomegaly (increased cardio-thoracic ratio from midpregnancy) (The earliest sign)
  • Placentomegaly
  • Ascites
  • Pleural or pericardial effusion
  • Subcutaneous edema (late sign)
  • Oligohydramnios (in late pregnancy) (unlike other causes which commonly related to polyhydramnios)

 

Hydrops fetalis

Hydropic fetalis due to Hb Bart's diisease

Hydropic placenta

Hydropic fetalis due to Hb Bart's diisease

Cardiomegaly

Markedly enlarged heart in fetal Hb Bart's diisease

Ascites

Ascites in fetal Hb Bart's diisease

 

Subcutaneous edema

Scalp edema in fetal Hb Bart's diisease

 

 

Anencephaly

  • The most common NTDs (1: 1000 births)
  • Ultrasound findings
  • Absent skull
  • Prominent orbit
  • Often related to polyhydramnios

Anencephaly

Base of skull contact with uterine wall / polyhydramnios

Anencephaly

No skull above the orbits : Spectacle sign

 

Anencephaly

Postnatal appearance of a term anencephalic fetus

 

 

Ventriculomegaly

  • Enlargement of cerebral ventricles or with increased pressure (hydrocephalus)
  • Most cases of marked ventriculomegaly caused by obstruction of aqueduct of Sylvious
  • Ventriculomegaly (> 10 mm)
  • Dilated 3rd ventricle (> 3 mm)
  • Dangling choroid plexus sign
  • Thin cerebral mantle

 

Hydrocephalus

Markedly enalarged lateral ventricles

Hydrocephalus

Autopsy : markedly enalarged lateral ventricles

 

Cystic Hygroma

  • Lymph collections due to obstruction, especially jugular lymph sac
  • Commonly associated with 45XO (70%), and trisomy 21, 18
  • Cyst at the posterolateral neck, septate or nonseptate
  • Lethal if hydrops occurs, but simple cyst may regress and disappear

 

Cystic hygroma

Septate cyst at the back of fetal neck

Cystic hygroma

Postnatal finding

Omphalocele

  • A protrusion of bowel / liver through abdominal wall at the umbilicus
  • The protrusion covered by a membrane
  • 50% associated with other anomalies, especially cardiac defects
  • If containing bowel, 80% associated with abnormal chromosomes
  • Liver-containing omphalocele: 20% associated with abnormal chromosomes

 

Omphalocele

Protruding mass containg liver with membrane covering

Omphalocele

Note: extra-abdominal mass with covering membrane

Gastroschisis

  • A protrusion of bowel (rarely other visceral organ) through a defect of the abdominal wall, typically to the right of the cord insertion
  • No membrane covers the mass
  • Not related to chromosome abnormalities or other anomalies other than GI

 

Gastrochisis

Free floating bowels in amniotic fluid

Gastrochisis

Postnatal appearance: no covering membrane

Hydronephrosis

  • > 75% related to renal abnormalities
  • Ureteropelvic junction (UPJ) obstruction is the most common cause: dilated renal pelvis (> 10 mm) and calyces, often bilateral
  • Thin renal parenchyma suggestive of poor renal function
  • Renal pelvic dilation < 10 mm is often a normal variant but needs follow up and slightly increased risk of Down syndrome

 

Hydronephrosis

Dilated renal pelvis and calyces

Hydronephrosis

Dilated renal pelvis and calyces