USG methods in obstetrics

1. Obstetrical
Ultrasound
Overview & First
Trimester
DR. JURY D. SHIRA,
PGT DMRD(NBE), DEPARTMENT OF RADIOLOGY, CIVIL HOSPITAL, SHILLONG
DATED: 3RD
MAY 2025

2. Ultrasound in
Ultrasonography
 In physics, the term "ultrasound" applies to
all acoustic energy (longitudinal,
mechanical wave) with a frequency
above the audible range of human
hearing. The audible range of sound is 20
hertz-20 kilohertz. Ultrasound is frequency
greater than 20 kilohertz.

3. Ultrasound Technology
 Principle of SONAR, used by bats and ships
 Generation of high-frequency sound waves
through a transducer
 Pulsed sound waves penetrate till structures
of different tissues densities is reached
 Reflected energy to the transducer is
amplified and displayed on a screen
 Detection of breathing, cardiac actions and
vessel pulsations

4. Obstetrical Ultrasound
 Introduced in the late 1950’s
ultrasonography is a safe, non-
invasive, accurate and cost-
effective means to investigate the
fetus
 Computer generated system that
uses sound waves integrated
through real time scanners placed
in contact with a gel medium to
the maternal abdomen
 The information from different
reflections are reconstructed to
provide a continuous picture of
the moving fetus on the monitor
screen

5. Risks and Side-effects
 Ultrasonography is generally considered a
"safe" imaging modality. However slight
detrimental effects have been occasionally
observed (see below). Diagnostic ultrasound
studies of the fetus are generally considered
to be safe during pregnancy. This diagnostic
procedure should be performed only when
there is a valid medical indication, and the
lowest possible ultrasonic exposure setting
should be used to gain the necessary
diagnostic information under the "as low as
reasonably achievable" or ALARA principle.

6.  World Health Organizations technical report
series 875(1998).supports that ultrasound is
harmless: "Diagnostic ultrasound is
recognized as a safe, effective, and highly
flexible imaging modality capable of
providing clinically relevant information
about most parts of the body in a rapid and
cost-effective fashion". Although there is no
evidence ultrasound could be harmful for
the fetus, US Food and Drug Administration
views promotion, selling, or leasing of
ultrasound equipment for making
"keepsake fetal videos" to be an
unapproved use of a medical device.

7.  Studies on the safety of ultrasound
A study at the Yale School of Medicine
found a correlation between prolonged
and frequent use of ultrasound and
abnormal neuronal migration in mice. A
meta-analysis of several ultrasonography
studies found no statistically significant
harmful effects from ultrasonography but
mentioned that there was a lack of data
on long-term substantive outcomes such
as neurodevelopment.

8. Types of Ultrasonography
Trans Abdominal
Ultrasonography
(TAS)
Trans Vaginal
Ultrasonography
(TVS)
Doppler Ultrasound Tissue Harmonic
Imaging (THI)
Three-dimensional
Ultrasound (3-D
USG

9. Trans Abdominal Ultrasound
(TAS)
• Major technique for imaging in 2nd
and 3rd
trimester
• Patient to have full bladder because
– Pushes the uterus out of the pelvis
– Provides an acoustic window
– Displaces pelvic bowel loop superiorly
• Real-time ultrasound equipment includes:
– Sector transducers, when access is limited
– Linear curved array transducers, for less distortion and
greater field of view

11. Trans Vaginal Ultrasound
(TVS)
 Method of choice for
 Monitoring infertility disorders
 Diagnosis of ectopic pregnancy
 Differentiation of normal and abnormal 1st
trimester pregnancy
 Diagnosis of congenital anomalies in 2nd
trimester
 Patient to have empty bladder because
 Uterus will be pushed posteriorly out of the field
of view of the transducer

12. Trans Vaginal Ultrasound (TVS)
cont
• Specially designed high frequency transducers
• Higher resolution images
• Favorable for obese patients or in early stage of
pregnancy
• Limitations include
– Reduced beam penetration
– More invasive nature of the technique

14. Doppler Ultrasonography
• Most widely employed for detection of:
– Fetal cardiac pulsation
– Pulsation in various fetal blood vessels
• Doppler waveform for useful information about
intra-uterine growth retardation
• Use remains controversial due to increased power

16. Tissue Harmonic Imaging
(THI)
 Processing of lower amplitude, higher frequency
waveforms accompanying fundamental frequency
 Lesser clutter and scatter
 Better visualization of fetal structure

17. Three-dimensional USG (3-
D)
 3-Dimensional “cleaner” image of the scanning
 Transducer captures series of images
 3-D processing done by Computer
 Significant improvement in identifying
 Cleft lips
 Spina bifida
 Polydactyl

19. WHO CAN PERFORM
OBSTETRIC
ULTRASONOGRAPHY?

20. A) The following qualified persons may
perform USG as far the provisions of the
Schedule i/ii/iii of IMC Act 1956 and
PCPNDT Act 1994
I. Radiologist with MD, DNB and DMRD
qualifications
II. Obstetric & Gynaecology
Specialist(MS/DNB/DGO) with 4 week of training
and 6months of experiences
III. Medical Officer(MBBS) with 6 months of training
in obstetric USG as mandate by PCPNDT Act 1994

21. PC-PNDT
Act 1994
 Pre-Conception and Pre-Natal Diagnostic Techniques
(Prohibition of Sex Selection) Act, 1994 an Act of the
Parliament of India enacted to stop female foeticides and
arrest the declining sex ratio in India. The act banned
prenatal sex determination.
Main provisions in the act are:-
1. The Act provides for the prohibition of sex selection, before or
after conception.
2. It regulates the use of pre-natal diagnostic techniques, like
ultrasound machine by allowing them their use only to
detect :- genetic abnormalities, metabolic disorders,
chromosomal abnormalities, certain congenital
malformations, haemoglobinopathies, Sex linked disorders.
3. No laboratory or centre or clinic will conduct any test including
ultrasonography for the purpose of determining the sex of
the foetus.
4. No person, including the one who is conducting the procedure
as per the law, will communicate the sex of the foetus to the
pregnant woman or her relatives by words, signs or any
other method.
5. Any person who puts an advertisement for pre-natal and pre-
conception sex determination facilities in the form of a notice,
circular, label, wrapper or any document, or advertises through
interior or other media in electronic or print form or engages in
any visible representation made by means of hoarding, wall
painting, signal, light, sound, can be imprisoned for up to three
years and fined Rs. 10,000.

22. INDICATIONS

25. Indications for
Ultrasonography
in Third Trimester
 Fetal growth monitoring
 Estimation of fetal weight
 Evaluation of fetal wellbeing
 Biophysical Profile
 Placenta position
 Amniotic fluid index
 Presentation and lie
 Follow up of anomalities in second
trimester
 Post dated(placental aging, fluid
and fetal status)

26. Post Partum
Indication of
Ultrasonography
PPH & Retained products of conception
Uterine rupture or dehiscene
Endometritis
Pelvic abscess
Bladder Injury
Ovarian vein thrombosis
Lochia abnormalities
CS scar evaluation

27. FIRST
TRIMESTER
PREGNANCY

28. First Trimester USG
• 0-4.3 weeks: no ultrasound findings
• 4.3-5.0 weeks:
• possible small gestational sac
• possible double decidual sac sign (DDSS)
• possible intradecidual sac sign (IDSS)
• 5.1-5.5 weeks:
• ​
gestational sac should be visible by this time
• 5.5-6.0 weeks
• yolk sac should be visible by this time
• gestational sac should be ~6 mm in diameter
• Double bleb sign
• Diamond ring sign(6weeks)

29. • >6.0 weeks
• fetal pole may be identifiable on endovaginal
ultrasound (1-2 mm)
• fetal heart rate (FHR) should be ~100-115 bpm
• gestational sac should be ~10 mm in diameter
• 6.5 weeks
• crown rump length (CRL) should be ~5 mm
• 7-8 weeks
• CRL is between 11-16 mm
• cephalad and caudal poles can be identified

30. • 8-9 weeks
• CRL is between 17-23 mm
• limb buds appear
• head can be seen as separate from the body
• 9-10 weeks
• CRL is between 23-32 mm
• fetal heart rate 170-180 bpm
• fetal movement can be seen
• a round hypoechoic structure in the fetal brain
represents a developing
embryonic/fetal rhombencephalon
11 weeks:
nuchal translucency may begin to be seen

31. Gestational Sac
USG
• Round or oval with
regular margin
• Eccentric toward one
side of endometrium
• May show yolksac or
embryo inside
• Wall is thick with
echogenic rim
• Intrauterine pregnancy

32. Double Decidual Sac Sign

34. PGS: Fluid filled
collection within the
uterus, often mistaken
for a GS
USG:
• Irregular shaped with pointed
edges and/or filled with
debris(beaking).
• Centrally located in endometrial
cavity
• Usually empty.
• Absent of double decidual sac
• Wall is thin
• Often seen in ectopic
pregnancy

35. Fetal Heart Rate on USG
 Visible heart activity: 43 days (6.1w)
 Normal heart rate at 6 weeks: 90-110 bpm
 At 8-9 weeks if nl heartbeat: 140-170bpm
 At 9 weeks:140-195 bpm(average=170)
 At 5-8 weeks a FHR <90 bpm is associated with a
high risk of miscarriage

38. USG Features and
Gestational Age in weeks

44. NUCHAL TRANSLUCENCY
 Fluid filled space in the back of the foetal neck.
 Its measurement is used in the screening of the
chromosomal abnormalities in the first trimester
 Ideal time for measuring NT is between 11 weeks
to 13weeks 6days of gestation (CRL between 45
to 84mm)
 Can be scan using TAS & TVS
 Fluid filled anechoic space at the back of the
foetal neck
 Normal NT measurement <2mm

45. NUCHAL TRANSLUCENCY MEASUREMENT

46. Measurement of Nuchal Translucency
Nuchal
Translucency

47. Evaluation of Uterus and Adnexal
structures
Uterus and cervical plug

48. COMMON
CONDITIONS IN
FIRST TRIMESTER
PREGNANCY

49. Obtetrica
l
perspecti
ve:
 Pregnancy losses
Threatened abortion, inevitable
abortion, incomplete abortion,
complete abortion, missed abortion,
septic abortion
 Ectopic Pregnancy
 Molar Pregnancy
 Hyperemesis gravidarum
 Early Pregnancy bleeding
 Chromosomal Abnormalities
 Structural Abnormalities
 Multiple Pregnancy

50. Sonologic
al
Perspectiv
e
 Early Pregnancy Failure
 Ectopic Pregnancy
 Molar Pregnancy
 Subchorionic Haemorrhage
 Multifetal pregnancy
 Foetal Anomalies
 Cervical Insufficiency

51. Early Pregnancy Failure
CRL>/=7MM WITH NO FOETAL HEART BEAT OR MEAN SAC DIAMETER >/=25MM
WITH NO EMBRYO

52. Ectopic Pregnancy:
 Implantation of fertilised
ovum outside of the
uterine cavity
 Risk of 1-2% of all the
pregnancy. The risk as
high as 18% first trimester
pregnancies with
bleeding
Locations:
 Tubal ectopic: 93-97%
(ampulla 65%, Isthmus
11%, fimbria 10%,
interstitial 3%)
 Ovarian ectopic: 0.5-1%
 Cervical ectopic: <1%
 Abdominal ectopic:
1.4%
 Scar(CS):Rare

54. USG of Ectopic Pregnancy
 Empty uterine cavity or no evidence of
intrauterine pregnancy(exception: heterotopic
pregnancy)
 Pseudogestational sac/decidual sac may be
seen in 10-20% of EP
 Thick echogenic endometrium
 Tube and ovary: simple adnexal cyst, complex
extraadnexal cyst/mass, solid hyperechoic
mass(not specific), tubal ring sign, ring of fire sign
 Peritoneal cavity: Free pelvic
fluid/hemoperitoneum in pouch of Douglas, free
fluid in hepatorenal recess/Morison’s pouch

56. RING
OF FIRE

57. TUBAL
RING
SIGN

58. MOLAR PREGNANCY:
The most common forms of
gestational trophoblastic
disease
 Types: Partial and Complete
 Partial: associated with abnormal
foetus/with foetal demise
 Complete: associated with
complete absence of foetus

59. Partial
Molar
Pregnancy
Greatly enlarged
placenta relative
to the size of the
uterine cavity
Cystic spaces
within the
placenta
Amniotic cavity
either empty or
contains
amorphous small
foetal echoes
which may be
surrounded by
thick rim of
pacental echoes
Colour doppler
may show high
velocity and low
impedance flow

60. Partial Molar
Pregnancy

61. Complete
Molar
Pregnancy
 Enlarged uterus
 Intrauterine mass with multiple
cystic spaces without any
associated of foetal part or foetal
echoes often refer to as
“snowstorm” or “bunch of
grapes” appearance
 Colour doppler shows high
velocity with low impedance flow

62. COMPLETE MOLAR
PREGNANCY

63. SUBCHORIONIC HAEMORRHAGE
 Perigestational haemorrhage and blood
collection outsidre the gestational sac that
accumulates between the uterine wall and the
chorionic membrane in pregnancy
 Frequent cause of bleeding in first trimester and
second trimester
 Causes: Trauma, maternal conditions(clotting
disorders, hypertension, hormonal changes,
infections/inflamations, previous H/O SCH

64. SCH:
HYPOECHOIC AREA
BETWEEN THE
GESTATIONAL SAC AND
UTERINE WALL

65. Grading of
Subchorionic
Haemorrhaage:
SMALL: <20% of the size of
gestational sac
Medium: 20-50% of the size of
gestational sac
Large: >50% of the size of
gestational sac (higher risk of
complications such as
miscarriage)

66. HYPOECHOIC CRESCENT SHAPED FLUID COLLECTION ADJACENT TO THE
GESTATIONAL SAC

67. SCH >50%
of GS size

68. Acute SCH
appears
hyperechoic
and may
cause difficulty
to differentiate
from the
adjacent
chorion

69. Hypoechoic
fluid collection
adjacent to
gestational
sac
with lack of
blood flow on
colour doppler

70. SCH can
be
septated

71. MULTIFETAL PREGNANCY
 Pregnancies with more than one fetus have
become an increasingly common
 Most multifetal pregnancies are twins
 The rate of twins occurring naturally is 1 in 80 births
 Multifetal pregnancies have higher rates of periatal
morbidity and mortality than singletons
 • Chorionicity is the major determining feature for
the inherent unique complications faced by multiple
gestations
 Fetal growth differences and congenital
malformations are increased in all types of multiple
gestations

72.  In monochorionic twins with a single demise, there
is a high risk of severe cerebral and other injuries in
the survivor
 Sonography permits the diagnosis of syndromes
unique to monochorionic twins, including twin-
twin transfusion syndrome, twin anemia
polycythemia sequence, twin reversed arterial
perfusion sequence, and conjoined twin

73. ZYGOSITY/CHORIONICITY
 Twins are either dizygotic or
monozygotic
 Approximately two-thirds are
dizygotic and one-third are
monozygotic
 Dizygotic twins occur when two
separate ova are fertilized by two
separate sperm
 Monozygotic twins occur when a
single ovum is fertilized by a single
sperm
 Dizygotic twins are always
dichorionic diamniotic, meaning
that each twin has its own
placenta (chorion), amnion and
amniotic fluid

74. There are three possible variations of
chorionicity for monozygotic twins,
who are genetically identical i.e.
-dichorionic
diamniotic
-monochorionic
diamniotic
-monochorionic
monoamniotic

75. USG

76. Fig: Line diagram of first-trimester pregnancies. Blue, Embryo;
brown, amnion; green, chorion; small black, yolk sac.

77. First-Trimester Twins. (A) Dichorionic diamniotic twins. Two separate gestational sacs, each with embryo
and yolk sac. Note the thin amnion separated from the chorion in each sac. (B) Monochorionic
diamniotic twins. Single gestational sac with two yolk sacs and two embryos (only one is shown). (C)
Monochorionic monoamniotic twins. Single gestational sac with two separate embryos and a single
surrounding amnion (white arrowhead). (D) Monochorionic monoamniotic conjoined twins. Single
gestational sac with a single amnion (white arrowhead), and a single large embryo that contains two
heart beats

78. COMPLICATIONS OF MULTIFETAL
PREGNANCY IN FIRST TRIMESTER
 Vanishing twin syndrome
 Twin-twin transfusion syndrome
 Conjoined twin
 Discordant growth
 Miscarriage(higher risk than singleton)
 SCH
 Chromosomal Anomalies(higher risk than
singleton)

79. CONJOINED TWIN
 Occurs when monozygotic twin embryo fails to
fully separate after the day 14 post fertilization
 Later the split, more fused the bodies will be
 Conjoined twins can be diagnosed in the late first
trimester; however, a detailed survey will be
required by 18 to 20 weeks gestation for the most
accurate evaluation of the degree of visceral
and vascular sharing

80. Fig: Picture shows conjoined of twin in the thorax
and abdomen

81. REFERENCES
1. Diagnostic ultrasound 5th
edition by
Carol Rumack Chapter 28 & 30
2. Textbook of ultrasound in obstetric
and gynaecology: practical
approach 1edition by Alfred
Abuhamad,MD Chapter 4
3. http://radiopaedia/articles/
4. http://nhmmeghalaya.nic.in/pcpndt
5. www.youtube.com/drsamimaginglibr
ary

82. THANK
YOU