This document summarizes normal and abnormal findings on obstetric ultrasound imaging during the first, second, and third trimesters of pregnancy. It describes the expected sonographic appearance of the gestational sac, yolk sac, embryo, fetal measurements, placenta, amniotic fluid, and common fetal anomalies. Abnormal findings that can be identified include anembryonic sac, miscarriage, ectopic pregnancy, fetal growth issues, placental abnormalities, and central nervous system, chest, abdominal, and heart defects.
5. Gestational sac
• After 5 weeks
• Well defined rounded or oval anechoic sac
• Site: within the endometrial cavity near the
uterine fundus
• Surrounded by chorio-decidual reaction > 2
mm.
• Double decidual sac sign (specific)
• MSD by > 1.2 mm /day
6.
7. Yolk Sac
• Spherical cystic structure that within the
gestational sac.
• Should be visualized :
- MSD > 20 mm by TA U/S
- MSD> 8 mm by TV U/S
8.
9. Embryo
• Double bleb sign is the earliest presentation
• Detected earlier by TVUS
• Should be visualized :
- MSD > 25 mm by TA U/S
- MSD> 16 mm by TV U/S
• Measured by Crown rump length (CRL)
14. Fetal measurements
• Mean sac diameter (MSD):
- Used when no embryo
- Average of 3 orthogonal planes
• Crown rump length (CRL):
- Most accurate in 1st trimester (till 12th week).
- Used as a baseline for assessment of fetal
growth for the rest of the pregnancy.
19. Anembryonic sac
- Distorted sac shape with low position.
- Poor chorio-decidual reaction (< 2mm) with
absence of double decidual sac sign.
- Growth < 1 mm/day
- Absence of yolk sac when MSD > 20 mm by
TA U/S or MSD> 8 mm by TV U/S
- Absence of fetal pole when MSD > 25 mm by
TA U/S or MSD> 16 mm by TV U/S
20.
21.
22. Abortion
• Threatened vaginal bleeding yet with live
embryo and closed cervix
• Inevitable open cervix with fetal tissue within
the cervical canal
• Missed GS within the uterus absent cardiac
activity
• Complete No retained products of conception.
• Incomplete retained products of conception.
23. Missed Abortion
• Absent cardiac activity when CRL > 5 mm by
TVUS
• GS within the endometrial cavity
• Closed cervix
31. Sub-chorionic hemorrhage
• Part of the picture of threatened abortion.
• Due to separation of chorion from the
myometrium.
• Before 20 wks
• US appearance varies with age:
- Acute hyper to isoechoic
- Subacute (clotted) hypoechoic
- Chronic (lysis) anechoic
32.
33. Ectopic Pregnancy
• Risk factors PID, IUCD , tubal surgery ,
endometriosis or previous ectopic pregnancy.
• Most common site isthmus of tube
• Other sites ovary , cervix , abdominal cavity
• Presence of intra-uterine pregnancy almost
excludes ectopic pregnancy (1 in 30000)
34. Ectopic Pregnancy
• Sure Signs of ectopic pregnancy:
- Live fetus outside the uterus
- GS with yolk sac outside the uterus
- GS outside the uterus with an echogenic ring
(tubal ring sign)
DD corpus luteum cyst :
- Thin walled
- Within ovary
35.
36.
37. Ectopic pregnancy
• Relative Signs of ectopic pregnancy:
Positive B-HCG +
- No intra-uterine pregnancy (43%)
- Pseudo-gestational sac (no double decidual
sac sign)
- Complex adnexal lesion (other than CL
cyst)(83%)
- Pelvic fluid collection (94 %)
42. Vesicular mole
• Benign form (no myometrial invasion)
• Complete mole no fetus
• Partial mole abnormal triploid fetus
• Classic US appearance (seen in second
trimester):
Uterus filled with innumerable variable sized
cysts (snow-storm appearance)
• Early appearance:
Solid echogenic mass
Anechoic fluid collection ( DD blighted ovum)
43.
44.
45. Invasive Mole
Choriocarcinoma
• Persistent or elevated B-HCG level following
molar evacuation.
• Invasion of myometrium (invasive mole)
• Invasion of myometrium , parametrium and
distant metasteses ( choriocarcionoma)
• US nodules in myometrium (insensitive)
• MRI more sensitive in detection of
myometrial invasion
50. Fetal Measurements
1) Biparietal diameter
• Measured at the level of thalamus
• From outer table of near cranium to the inner table
of far cranium
• Affected by head shape
51. Fetal Measurements
2) Head Circumference
• Measured at same level as BPD
• Outer circumference of the cranium
• Independent of head shape
52.
53. Fetal Measurements
3) Abdominal Circumference
• Measured at the level of intra-hepatic portion of
umblical vein (portal vein)
• Outer circumference of the abdomen
57. Fetal Measurements
• Composite age (average of all parameters) and
estimated fetal weight (EFW) is more accurate than
any single parameter.
• Much more accurate in early pregnancy.
• All subsequent fetal examinations are compared
with 1st examination to assess fetal growth.
58. IUGR
• Diagnosed when EFW is less than the 6th
percentile for gestational age
• Or between 6th and 20th percentile +
oligohydraminos and maternal hypertension
• Normal fetal weigt gain in 3rd trimester is 100-
200 gm week
62. Fetal Doppler
2) Umblical Artery RI
• RI < 0.7
• If > 0.7 impaired feto-placental circulation
• Two arteries + one vein
• Single artery umblical artery ass. with congenital
anomalies
68. Cervical Competence
• Assessed in the beginning of 2nd trimester
• Best assessed by trans-vaginal or trans-labial
US on empty bladder.
• Full bladder falsely elongated the cervical
canal.
• Cervical length > 3 cm
69.
70.
71. Cervical Incompetence
• Cervical length < 25 mm
• Cervical canal diameter > 8 mm
• Funneling of internal os
• Bulging of membranes
75. Placental Grading
(Grade 0)
• Early 2nd trimester
• Uniform moderate echogenicity
• Smooth chorionic plate without indentations
76.
77. Placental Grading
(Grade I )
• Mid 2nd trimester – early 3rd trimester
• Subtle indentations of chorionic plate
• Small, diffuse calcifications randomly
dispersed in placenta
78.
79. Placental Grading
(Grade II )
• Late 3rd trimester
• Larger indentations along chorionic plate
• Larger calcifications
80.
81. Placental Grading
(Grade III )
• 39 wks – post dates
• Complete indentations of chorionic plate
through to the basilar plate creating
“cotyledons” (portions of placenta separated
by the indentations)
• More irregular calcifications with significant
shadowing
82.
83. Placenta Previa
• The placenta covers all or part of the internal
os.
• Low lying within 2 cm of os
• 45 % in 1st and 2nd trimester then most of
them resolves.
• Diagnosed in 3rd trimester
• Diagnosed by TVUS or trans-perineal US on an
empty bladder.
84.
85.
86. Placental Abruption
• Ass. With maternal hypertension
• Separation of the placenta from underlying
myometrium retro-placental hematoma
• US appearance varies with age:
- Acute hyper to isoechoic (identified by
placental thickening and disruption of retro-
placental complex)
- Subacute (clotted) hypoechoic
- Chronic (lysis) anechoic
87.
88.
89. Placental Anomalies
• Adherent placenta (acreta):
- If infiltrates myometrium (increta) and serosa
(percreta)
- US loss of retroplacental complex
retroplacental complex within bladder wall
- Best diagnosed by MRI
Uterine bulge- heterogenous placental signal-
intraplacental dark band -focal interruption of
myometrial wall – UB tenting
90.
91.
92.
93. Placental anomalies
• Circumvallate placenta : rolled placental
edges due to smaller chorionic plate (placental
shelf)
• Succenturiate placenta : small accessory lobe
• Bilobed placenta: two equal sized lobes
• Placenta membranacea: thin placenta
covering nearly all the uterine wall
• Chorioangioma: Benign vascular placental
mass… If large high cardiac output HF
94.
95.
96.
97.
98.
99. Amniotic fluid
• AFI (N= 5-20) =
Sum of vertical diameters of the deepest
pockets in the 4 quadrants ( not containing
fetal parts or umblical cord)
• Polyhydraminos :
AFI > 20 , single pocket > 8 , fetus not touching
any uterine wall after 24 wks
• Oligohydraminos:
AFI < 5 , largest pocket < 1 , crowded fetal parts
100.
101.
102. Twin Pregnancy
• Amniocity : no of amniotic sacs
• Chorionicity: no of placentas
• Risk of anomalies:
Monoamniotic > diamniotic monochorionic >
diamniotic dichorionic
• Features of diamniocity:
- Separate placenta
- Different sex
- Chorion extending into the inter-twin membrane
(lambda sign)
103.
104.
105.
106. Twin Transfusion Syndrome
• Shunting through vascular connection in
placenta
• Only if monochorionic
• One fetus IUGR + oligohydraminos
• Other hydrops + polyhdraminos
107.
108. Twin Embolisation syndrome
• Demised Twin
Blood products from dead fetus shunted
through placenta to live fetus
DIC
116. CNS anomalies
2) Presence of Falx:
If absent
absent cortical mantle hydrancepaly
present cortical mantle holoprosencephaly
117.
118.
119.
120. CNS anomalies
3) Trans-thalamic plane:
- Measure BPD , HC
- Detect microcephaly , macrocephaly and
other structural abnormalities
121.
122.
123. CNS anomalies
4) Trans-ventricular plane:
- Dominant feature is choroid plexus within the
ventricular atrium.
- Ventriculomegaly atrial diameter > 10 mm
and separation of corid plexus from
ventricular wall by > 3 mm .
- Most common causes are Chiari II and
aqueductal stenosis.
124.
125.
126. CNS anomalies
5) Trans-cerebellar plane:
- Assess cerebellar hemispheres (hypoplastic in Dandy Walker)
- Assess Cisterna Magna (N= 2-11mm)
If < 2 mm Chiari II (+ small posterior fossa with banana
shaped cerebellum + frontal bossing “ lemon sign” +
hydrocephalus + myelomengiocele)
If > 11mm a)communicating with fourth ventricle
Dandy Walker
b)not communicating with fourth ventricle
Arachnoid cyst or mega cisterna magna
137. CNS anomalies
7) Spina Bifida:
- Outward convergence of vertebral laminae
- Defect in overlying soft tissues
- Protruding sac contain fluid and other neural structures
(menigocele , myelomenigocele)
- Associated with other anomalies e.g. Chiari II
142. Chest Anomalies
( Congenital Diaphragmatic hernia)
• Abdominal contents
within the chest
• Either postero-lateral
(Bochdalek) or antro-
medial (Morgagni)
• US fluid filled
multicystic mass
displacing the heart
+ absence of stomach in
abdomen
143. Chest Anomalies
( Cystic adenomatoid malformation)
• Multi-cystic lesion
• Cysts vary fro
microscopic to 2 cm
144. Chest Anomalies
( Pulmonary Sequestration)
• Mass of sequestrated
lung tissue.
• Extra-lobar type more
frequently detected by
fetal US
• US Homogenous
echogenic solid lung
mass displacing the
mediastinum
145. Fetal Heart Assessment
• Assessed in four chamber view on axial scan
• Ventricles are nearly equal in size
• Ventricles smaller than atria
• Apex is directed to the left at 45
• Any abnormality fetal echo is requested
155. Bladder
• Should be observed to
fill and empty.
• Related to the amniotic
fluid index
• PUV keyhole sign +
hydronephrosis
156. Abdominal Herniations
Gastroschisis
- On the side of umblical
cord
- No covering
membranes
- Normal cord insertion
- Isolated
Omphalocele
- Midline (at umblicus)
- Covered by membranes
- The cord inserts in it.
- Associated anomalies
are common
157.
158.
159. Skeletal Anomalies
US findings ass. with skeletal dysplasia:
- Extremity bone shortening (short femur)
- Fractures
- Bowing
- Demineralization
- Small thorax