ultrasound in obstetrics

2. •developed by professor Langevin for the French and
British admiralties during the first world war to combat the
growing menace of submarines.
•It was formerly referred to as SONAR which stands for
“sound, navigation and ranging”

3. •Sir Ian Donald was the first to demonstrate and document
the application of this technology to medical diagnosis.
•His pioneering efforts were published in The Lancet of 7
June 1958 which described his experience with ultrasound
for the diagnosis of a large ovarian cyst

4. •An ultrasound scanner consists of transducers (probes) that transmit
and receive ultrasound waves, a screen to view the image and its
technical data, and a variably sophisticated control panel.

5. • Ultrasound waves result from an inverse piezo-electric
effect.
• The piezo-electric effect refers to the phenomenon that
takes place when pressure is applied to the surface of
certain crystals referred to as piezo-electric materials :
the mechanical pressure produces an electric current.

6. •Inversely, when an electrical pulse is applied to piezo-
electric material, a mechanical wave results and this
mechanical wave is the ultrasound beam.
•When these wave meet the tissue interface, they are
reflected back to the transducer and converted to an electric
signal, which is processed and displayed as the ultrasound
image on the monitor.
•The amount of beam reflected back is proportionate to the
difference in the acoustic densities of the tissues meeting at
the interface

7. • When the acoustic densities are markedly different such as
when striking calcification, bone, stones and air, nearly the
whole beam is reflected back and the image is echo-rich.

8. •If the acoustic density differences are small, low level
echoes result and if the acoustic densities are identical as in
homogeneous fluids like blood, amniotic fluid and urine, the
entire wave is transmitted and none is reflected resulting in
an echo-free image.
•Because air is a poor transmitter of high-frequency sound
waves, soluble gel is applied to the skin to act as coupling
agent.
•The processor computes the location (depth) of the signal
based on time differences between transmitting and
receiving.

9. • Obstetric ultrasound employs frequencies of 2 to 15
Mhz.
• Higher frequency transducers have higher spatial
resolution. This means they can better differentiate two
closely located side-by-side spots in the region of
interest.
• The penetration of high frequency wave is however
limited. Therefore, high frequency probes are used to
look at near structures and lower frequency probes are
used to study tissues at depth.

10. •Abdominal transducers use a frequency of 2 to 6.5 MHz
and transvaginal transducers use frequencies of 5 to 15
MHz.
•Obstetric ultrasound uses a largely abdominal approach.
•Transvaginal scanning is used in the first trimester for more
accurate information on early pregnancy complications and
delineation of fetal morphology, assessing the cervical
length and other features of incompetence, delineation of
cranial anatomy in the deeply engaged head and in some
situations of suspected placenta previa and vasa previa.

11. •Conventionally, the left of the screen indicates the head-
end of the patient in a longitudinal section or the right side of
the patient in a transverse section. The top of the screen is
anterior and the bottom posterior.
•When imaging the fetus in the second and third trimesters,
these orientations are no longer relevant.

12. •Echo-free structures and lesions are also referred to as
anechoic, sonolucent, fluid or echolucent.
•Echo-rich structures are also called heperechoic,
echogenic, echo-bright or solid.
•Structures with few echoes are referred to as echo-poor,
echopenic or hypoechoic.

13. •A-mode studies were the most primitive forms of
ultrasound imaging and consisted of a graph indicating
reflectors at the level of their depth.
•These are no longer used in obstetrics.

14. •B-mode studies are currently in use and are what we mean
by conventional ultrasound now.
• These indicate reflections arranged along two axes in the
region of interest.
•B-mode studies currently use a grey scale which reflects
the intensity of the signal and imparts texture to the image.
The other attribute of B-mode studies is real-time.

15. •In the real-time mode, the image moves in the
same manner as the region of interest moves in
real life.
•The conventional ultrasound scan today is,
therefore, a real-time grey-scale B-mode study.
This is also known as 2D study.

16. •It is now possible to add a third dimension to the image
which is made possible by a special transducer and
computer software arrangement, and is referred to as 3D
ultrasound.
•Real-time 3D ultrasound is known as 4D ultrasound.

17. •The tern M-mode refers to a motion mode in B-
mode studies.
•This is currently employed in obstetrics to
evaluate fetal cardiac motion to assess heart rate
and rhythm as well as for studying the excursions
of the cardiac valves and the myocardium.

18. • Confirm an intrauterine pregnancy
• Evaluate a suspected ectopic pregnancy
• Define the cause of vaginal bleeding
• Estimate gestational age
• Diagnose or evaluate multifetal gestations
• Confirm cardiac activity
• Assist chorionic villus sampling, embryo
transfer, and localization and removal of an
intrauterine device

19. •Assess for certain fetal anomalies, such as
anencephaly, in high-risk patients
•Evaluate maternal pelvic masses and/or uterine
abnormalities
•Measure nuchal translucency when part of a
screening program for fetal aneuploidy
•Evaluate suspected gestational trophoblastic
disease

20. EMBRYONIC EVENTS
•day 14: ovulation
•day 15: fertilization
•day 18: morula stage
•day 20: blastocyst stage- beginning of
implantation
•Day 23: implantation complete
•Days 27-28: formation of secondary yolk sac
•Days 21-28: proliferation of syncytiotrophoblast

21. ULTRASOUND FINDINGS
•Implantation- conceptus measures 0.1mm &
cannot be detected by the available ultrasound
equipment
•trophoblastic flow with transvaginal color flow
doppler – increased blood flow velocity in the
endometrium is due to invasion of decidua by
chorionic villi.

22. •EMBRYONIC EVENTS
•day 29-30: gastrulation; formation of 3 primary germ
layers
•days 31-42: neurolation; formation of neural plate &
neural tube
•Day 35: primitive cardiovascular system consisting of
heart & a vascular network in the embryo, yolk sac,
connecting stalk & chorion

23. ULTRASOUND FINDINGS
Gestational sac:
Frequency at least 5 MHZ with TVS
Size-2-3mm MSD
Wks-4wks3d to 4wks 5d
yolk sac:
5.5 wks GA - MSD 8mm (TVS)
can be earliest seen with MSD 5mm & should always
be evident by MSD 8mm
6 to 7 wks GA- MSD 15 to 20 mm (TAS)

24. Methods Serum B hcg level in IU/ml
TVS--------- ------1000 TO 2000
TA-------------------6000
Yolk sac------------7000
Embryo---------------11,000

25. Small fluid collection surrounded completely by an
echogenic rim
Echogenecity of rim should exceed the level of
myometrial echoes
Position- fundus or in mid to upper uterus & is
always abutting the endometrial canal
GA in days=Gestational sac (MSD) size in mm +30

26. THRESHOLD LEVEL:
• lowest B-HCG level by which a normal
intrauterine gestational sac is possible to be
identified
DISCRIMINATORY LEVEL:
• level above which gestational sac must be
visualized
• 1000 MIU/ml for TVS

27. •Confirms- early intrauterine pregnancy
•1st recognizable structure inside the gestational sac &
should be seen when MSD is 8-10mm.
•Normal yolk sac diameter in 1st trimester 3-6mm
•Increases steadily by 0.1mm per day until 10 wks GA to a
maximum of 5 to 6mm
•Abnormal yolk sac size & morphology cannot be used as
absolute predictors of pregnancy outcome & need serial
evaluation to confirm or exclude an abnormal outcome

28. • following changes assessed by 2D US are related to
spontaneous abortion procedure
 absence of yolk sac
Too large - >6mm
Too small - <3mm
Irregular shape- mainly wrinkled with indented walls
Degenerative changes- abundant calcifications with
decreased translucency of yolk sac
Number of yolk sacs- has to be equal to the number of
the embryos

30. •MSD=10mm
•Consists of decidua parietalis( lining the uterine
cavity) & decidua capsularis (lining the gestational
sac) seen as 2 concentric rings surrounding an
anechoic gestational sac
•TAS-5 to 6 wks GA
•Confirms intrauterine pregnancy

32. •Gestational sac in which embryo failed to develop or died at a
stage too early to visualize
•Diagnosis- absence of embryonic echoes within the gestationl
sac, large enough for such structures to be visualized,
independent of the clinical data or menstrual cycle.
•If the volume of the sac is 2.5ml & is not increasing in size by
at least 75% over a period of 1 week, the definition of this
pathological condition in early pregnancy is a blighted ovum.
•A large empty sac usually measures 12-18mm in diameter

34. By Transabdominal approach
By TVS
MSD development
10 mm No double decidual sign
20 mm No yolk sac
25 mm No embryo with cardiac
activity
MSD development
8 mm no Yolk sac
16 mm No cardiac activity

35. METHODS GA in wks MSD in mm CRL
TVS 6 TO 6.5 13 TO 18 4mm
TAS 8 25 9mm

36. •If CRL is less + no cardiac activity
-Expectant management with follow up usg
-Use B hcg for follow up
•If CRL is more + no cardiac activity
-Non viable gestation is likely

37. GA in wks HEART RATE
6 110 TO 115
8 140 TO 170
9 137 TO 144

38. structure Gestational
age
spine 7-8wks
Upper limbs 7 wks
Lower limbs 8 wks
Feet & hands End of 10th
wk
Fingers & toes 11 wks
Maxilla & mandible 9th wk

39. •The distance from the top of the head( crown) to
the bottom of the buttocks (rump)
•Measured with embryo in neutral position with no
flexion or extension
•Mean of 3 readings
• to assess gestational age from 5 wks 3 days to
13 wks 6days

41. GESTATIONAL AGE IN
WEEKS
CRL in cm
6.1 0.4
7.2 1.0
8.0 1.9
9.2 2.5
9.6 2.9
10.5 4.0
12.2 5.5
13.2 6.9
14.0 8.0
Gestational age( in weeks) = CRL (cm) + 6.5

42. 1st trimester ultrasound
<= 5days discrepancy between
LMP & US estimate of GA
>5 days discrepancy between
LMP & US estimate of GA
Choose LMP derived GA
prediction
Choose US derived GA
prediction

43. •sonographic appearance of the subcutaneous
accumulation of fluid in in the region of fetal neck.
•Anechoic stripe
•seen in all fetuses in early pregnancy.

44. •Chromosomal abnormality
• cardiovascular (cardial septal defect, cardiac failure)
•Pulmonary (diaphragmatic hernia), Increased in intra
thoracic pressure, mediastinal compression causing
venous congestion
•Renal & abdominal wall defects, skeletal dysplasia
,infections, metabolic & hematologic disorders
•Connective tissue abnormalities, alteration of extracellular
matrix of skin (trisomy 21)
•Delay in development of Lymphatic system(turners
syndrome),
•Fetal hypo proteinemia

46. • midline sagittal section
• If facing towards the transducer- the fetal nasal
bridge and the nasal tip should be visible in same view
• If facing away from the transducer- the medulla ,pons
and the thalamus should be visible in the same view.
•11wks to 13wks 6days
•CRL 45-84mm
•Magnification of 75% such that only head & thorax occupy
the whole screen

47. •At the widest space of the NT
•Calipers placed “on to on” in transonic space
perpendicular to long axis of fetus
•Biggest of 3 measurements
•TAS preferable, but depending on fetal position
TVS can be done
•Exclude the presence of umbilical cord near neck
•Fetal neck in neutral position

49. NORMAL VALUES
Cut off at 3.5mm across 11-13 wks
CRL NT
45mm 1.2 -2.1mm
84mm 1.9-2.7mm

50. •ACOG recommends that patients who have fetal NT
>=3.5mm in 1st trimester despite a negative aneuploidy
screen or normal fetal chromosomes should be offerd a
targeted ultrasound examination,fetal echocardiogram
or both.
•A pregnancy should never be terminated on the basis
of this finding alone.

52. •downs syndrome
•turner’s syndrome
•trisomy 18
•trisomy 13
•triploidy
various other fetal defects and genetic syndromes with
normal no. of chromosomes.

53. Absent or hypoplastic in:
o69% fetuses with trisomy 21
o50% of trisomy 18
o40% trisomy 13
o1.4% of chromosomally normal fetuses

55. •Transducer should be parallel to the direction of nose
•3 lines will be visible
 skin- top line
Echogenic nasal bone just below this which is thicker
than the overlying skin
3rd line in front of nose – tip of nose

56. NASAL BONE
PRESENT:
if more echogenic
than overlying skin
ABSENT:
Not seen or
echogenicity <=
skin

57. •Assessment of nasal bone is not yet recommended in
routine clinical practice
•studies show that
Nasal bone not
incorporated in 1st
trimester screening
Nasal bone incorporated
DETECTION RATE FOR
DOWNS SYNDROME
81.8%
FALSE POSITIVE 5.4%
90.9%
FALSE POSITIVE 3.7%

58. •It is the quantification of the flat facial profile seen in
fetuses with trisomy 21
•As maxilla is small & set back in these fetuses, the angle
becomes wider
•INCREASED IN:
5% euploid fetuses
45% trisomy 21
55% trisomy 18
45% trisomy 13

59. •Angle between line drawn along superior surface of the
palate & a line drawn from anterosuperior corner of the
maxilla to the anterior surface of frontal bone

60. •It is the quantification of the flat facial profile seen in
fetuses with trisomy 21
•As maxilla is small & set back in these fetuses, the angle
becomes wider
•INCREASED IN:
5% euploid fetuses
45% trisomy 21
55% trisomy 18
45% trisomy 13

61. •Angle decreases with increase in CRL
•Assessment of facial angle in addition to NT inreases
detection rate of trisomy 21 from 90 to 94%
GA CRL FMF ANGLE
11weeks 45mm 83
13weeks 6 days 84mm 75

62. •Abnorml ductus venosis flow in the 11-13wks 6days scan
is associated with chromosomal anomalies, cardiac
abnormalities, & adverse fetal outcomes
•Reversed flow in a wave is observed in:
• 3.7% euploid fetuses
• 70% fetuses with trisomy 21, 18 & 13.
•However in 80% fetuses with reversed a waves pregnancy
has a normal outcome
•When combined with NT- detection rate of trisomy 21
increases from 94 to 97%

63. •Increases risk of trisomy 21 & cardiac defects
•The incidence is correlated with nuchal thickening &
decreases with increasing CRL.
•Fetus should not be moving
•Apical 4 chamber view is obtained & magnified so that
entire screen is occupied by thorax
•Fetuses with TR with normal karyotype should be
followed carefully to assess for cardiac anomalies.

64. COMPLETE MOLE
•Enlarged uterus
•Classic sonographic apperarence- solid collection of
echoes with numerous small (3-10mm) anechoic spaces
(snowstorm or granular apperance)
•Molar tissue- bunch of grapes sign which represents
hydropic swelling of trophoblastic villi
•Variable apperance
•No identifiable fetal tissue

65. COMPLETE MOLE

66. PARTIAL MOLE
•placenta enlarged & contains areas of multiple diffuse
anechoic lesions
•Fetus with severe structural abnormalities or IUGR,
oligohydramnios, or deformed gestational sac may be
noted

67. PARTIAL MOLE

68. TUBAL/ ADNEXIAL RING SIGN OR BAGEL/ DONUT
SIGN
• extrauterine gestational sac (fluid filled) with echogenic
ring which surrounds an unruptured ectopic pregnancy.
• has a 95% positive predictive value for ectopic pregnancy

70. TWIN PEAK SIGN/ LAMBDA SIGN
•triangular projection of trophoblastic tissue isoechoic with placenta
insinuating between the layers of inter twin membrane from the
placental surface
•100% predictive of dichorionic pregnancy
•In 2nd trimester regression of chorionic frondosum leads to the gradual
loss of lambda sign
T SIGN
•Refers to lack of chorion extending between the layers of inter twin
membrane denoting a monochorionic pregnancy
•The intertwin membrane comes to an abrupt halt at the edge in a T
configuration

72. •Ian Donald’s practical obstetric problems, 7th edition
•William’s obstetrics, 24th edition
•Peter W. Callen ultrasonography in obstetrics and
gynaecology
•Donald School textbook of of ultrasound in Obstetrics
and Gynaecology 2nd edition

73. THANK YOU