{tab=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

 

{tab=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

{tab=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

   

   

{tab=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

{tab=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

   

{tab=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

{/tabs}