Published on February 17, 2014
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 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 5 weeks Endometrial thickening, no obvious sac Gestational ring, white echogenic rim
Double decidual sac sign 5 weeks Usually seen at 5-6 weeks Note yok sac 6 weeks 7-8 weeks Note: yok sac and early embryo Rapid growth of embryo and amnion 8 weeks 10 weeks Fetal body compartments : head trunk limbs 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 5 weeks Usually seen at 5-6 weeks Note yok sac Mean Sac Diameter (MSD) • • MSD : Average gestational sac diameter = width + depth + length / 3 • When MSD > 25 mm. GA (days) = MSD + 30 MSD closely related to early GA
Mean sac diameter Mean sac diameter Longitudinal 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) • Short CRL related to high abortion rate and aneuploidy • Head, trunk, limbs can be identified from 8 weeks Useful only in the first trimester Amnion • • Seen from 7-8 weeks (TVS) • Fast growing, finally embryo is in the sac • Yolk sac is outside Beginning with double bleb sign (yolk sac and amnionic sac)
Yolk sac Yolk sac Yolk sac adjacent to fetal echo in early gestation 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 Physiologic omphalocele Prominent at 8-9 weeks 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 Nuchal translucency Normal measured at 11 weeks Thickened nuchal translucency Nuchal translucency Nuchal translucency Thickened nuchal translucency at 14 weeks Thickened nuchal translucency after abortion Early Pregnancy Complications Threatened Abortion • Ultrasound examinations see if viable or nonviable pregnancy • Viable fetus with normal heart beat : very good prognosis • Nonviable:
o blighted ovum o missed / incomplete abortion o fetal death o ectopic pregnancy o molar pregnancy Threatened abortion Threatened abortion Normal fetus at 11 weeks 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 Blighted ovum Gestational sac without embryo, subcorion hematoma 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 Ectopic pregnancy Floating dilated fallopian tube in free fluid Gestational sac with embryo and yolk sac in the tube Ectopic pregnancy Adnexal omplex mass of blood clot and concepitus • • Molar Pregnancy o o Ultrasound findings: o Snow storm pattern or o Numerous small cystic echo or No fetus
o Placental-like echo o May show complex area of blood clot Molar pregnancy Molar pregnancy Numerous small cystic space in uterine cavity mass Snow storm appearance Molar pregnancy The opened uterine specimen after hysterectomy 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 Mean sac diameter Longitudinal diameter Transverse diameter and depth Crown-Rump Length (CRL) • • The most accurate parameter for GA (+ 3-7 days) • 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 Most accurate during 6.5-10 weeks
Crown-rump length Crown-rump length 8 weeks 9 weeks Crown-rump length 12 weeks Biparietal Diameter (BPD) • • The best parameter during 2nd trimester (+ 7-11 days during 14-26 weeks) • Ovoid and symmetry • Thalamus • Midline echo / third ventricle Technique: the distance from outer-to-inner skull table in the plane visualized of
• 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 Biparietal diameter Standard plane for BPD measurement Standard plane for BPD measurement Dolichocephaly Brachycephaly BPD not proper for gestatational age calculation 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 Abdominal circumference Standard plane for abdominal circumference Standard plane for abdominal circumference measurement 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 Femur lenght Standard plane for femur length measurement 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) Fetal Growth Restriction (FGR) FGR due to twin-to-twin transfusion syndrome FGR due to twin-to-twin transfusion syndrome 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 Polyhydramnios Four quadrant deepest verical pocket measurement 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 o Partial previa: placenta covers a portion of internal os (indistinguishable from marginal previa in o prenatal practice) o Total previa: placenta covers the os o Low-lying placenta: nearly the os, not true previa and vaginal deliver is possible o Ultrasound: should be done with an empty bladder because the cervix is spuriously long by full bladder leading to false previa o Most placenta previa diagnosed in the 2nd trimester is away from the os at term o The cervix could be visualized using TAS, TVS or transperineal approach
Placenta previa totalis Placenta previa totalis Standard plane for BPD measurement Standard plane for BPD measurement False placenta previa totalis False placenta previa totalis Full bladder compress lower segment, simulating placenta previa totalis The same case (after voiding) Placental Abruption o o cystic, complex, or hypoechoic areas may be seen between placenta and uterine wall o reveal type may be not diagnosed Placental thickening
retro placental hematoma may be isoechoic like placenta o Placental abruption Placental abruption Placental abruption Placental abruption 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 placenta Hydropic fetalis due to Hb Bart's diisease Hydropic fetalis due to Hb Bart's diisease Cardiomegaly Ascites Markedly enlarged heart in fetal Hb Bart's diisease 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 Anencephaly Base of skull contact with uterine wall / polyhydramnios 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 Hydrocephalus Markedly enalarged lateral ventricles Autopsy : markedly enalarged lateral ventricles Cystic Hygroma • • Lymph collections due to obstruction, especially jugular lymph sac • Cyst at the posterolateral neck, septate or nonseptate • Lethal if hydrops occurs, but simple cyst may regress and disappear Commonly associated with 45XO (70%), and trisomy 21, 18
Cystic hygroma Cystic hygroma Septate cyst at the back of fetal neck 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 Omphalocele Protruding mass containg liver with membrane covering 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 Gastrochisis Free floating bowels in amniotic fluid 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 Hydronephrosis Dilated renal pelvis and calyces Dilated renal pelvis and calyces
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