OBSTETRIC ULTRASOUND TECHNIQUES

FETAL AGE ESTIMATION

1

2

Sequence• Introduction to Obstetric Ultrasound

• Technology

• Common Uses

• Types of USG

• Indications of Ultrasound Examination

• Application of Ultrasound in Trimesters

• Fetal Age Estimation

• Conclusion

• Q & A session

3

4

Introduction to Obstetric Ultrasound

• Use of ultrasound scans in pregnancy

• Introduced in late 1950s

• Provision of good information about the fetus and its environment

• Determining early intervention or conservative management

• Safe, non-invasive, accurate, and cost-effective investigation in fetus

• Important role in care of pregnant women5

6

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 through real-time ultrasonography

Transducer

Transmitted pulse

Received pulse

Object

Common Uses of Obstetric USG

• Obstetrical ultrasound is a useful clinical test to:

– Establish the presence of a living embryo/fetus

– Estimate the age of the pregnancy

– Diagnose congenital abnormalities of the fetus

– Evaluate the position of the fetus

– Evaluate the position of the placenta

8

– Determine if there are multiple pregnancies

– Determine the amount of amniotic fluid around the baby

– Check for opening or shortening of the cervix or mouth of the womb

– Assess fetal growth

– Assess fetal well-being

– Suspected hydatidiform mole

9

Common Uses of Obstetric USG cont

– Suspected fetal death– Suspected uterine abnormality– UCD localization– Ovarian follicle development surveillance– Biophysical profile after 28 weeks of gestation– Observation of intra-partum events– Suspected poly- or oligohydramnios– Suspected abruptio placenta– Adjunct to external version from breech to vertex

presentation

10

Common Uses of Obstetric USG cont

Types of Ultrasonography

• Trans Abdominal Ultrasonography (TAS)

• Trans Vaginal Ultrasonography (TVS)

• Doppler Ultrasound

• Tissue Harmonic Imaging (THI)

• Three-dimensional Ultrasound (3-D USG)

11

Trans Abdominal Ultrasound (TAS)

12

• 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

13

Trans Vaginal Ultrasound (TVS)

14

• 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

• 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

15

Trans Vaginal Ultrasound (TVS) cont

16

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

17

18

Tissue Harmonic Imaging (THI)

• Processing of lower amplitude, higher frequency waveforms accompanying fundamental frequency

• Lesser clutter and scatter

• Better visualization of fetal structure

19

20

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

21

22

Application of Ultrasound in Trimesters

• First Trimester– Commonly performed at 9-12 weeks

• 2nd and 3rd Trimester– Commonly performed at 18-20 weeks

23

Obstetric USG in 1st Trimester

• Identification of Gestational sac and Embryo

24First trimester fetus and yolk sac

• Recording the presence or absence of fetal life

25

Obstetric USG in 1st Trimester cont

Embryo 4 weeks

• Identification and documenting the fetal number

26

Two gestational sacs, each containing a yolk sac

Obstetric USG in 1st Trimester cont

• Evaluation of Uterus and Adnexal structures

27

Obstetric USG in 1st Trimester cont

Uterus and cervical plug

• Measurement of Nuchal Translucency

28

Obstetric USG in 1st Trimester cont

Nuchal Translucency

29Triplet with sub-chorionic bleeding

30

31

Twin pregnancy28 mm CRL in 10 weeks

• Fetal life, number and presentation• Amount of amniotic fluid

32

Obstetric USG in 2nd and 3rd Trimester

• Record Placental localization• Establishment of fetal age and growth by fetal

biometry including– Bi-parietal Diameter– Head Circumference– Femur Length– Abdominal Circumference

33

Obstetric USG in 2nd and 3rd Trimester cont

• Evaluation of the uterus and adnexal structures

• Evaluation of fetal anatomic structures : – Cerebellum and Cerebral ventricles– Spine – Stomach-bowel, abdominal wall at the area of the

umbilical cord insertion– Bladder and kidney– All four Limbs– Four chamber view of the heart

34

Obstetric USG in 2nd and 3rd Trimester cont

35Fetal Cardiac Structure

Fetal Age Estimation

• Assessment of gestational age is fundamental to obstetric care

• Ultrasound is a reliable method for establishing the length of pregnancy

36

Fetal Age Estimation in 1st Trimester

• Identification of Gestational sac– Correlation of MSD and CRL with menstrual age

• Visualizing of Embryo by TVS and TAS– Estimation of gestational age by crown-rump length

• Nuchal Translucency assessment in 1st trimester

37

38

• Bi-parietal diameter measurement– Around 09 weeks until end of pregnancy

• Head Circumference measurement– Gestational age prediction when abnormal skull shape– Measured on same plane as Bi-parietal diameter

• Abdominal Circumference measurement– Measurement similar to head circumference– Less accurate for establishing gestational age– Perpendicular plane to the long axis of fetus

39

Fetal Age Estimation in 2nd & 3rd Trimester

40

Bi-parietal diameter and head circumference measurements

Fetal Age Estimation in 2nd & 3rd Trimester

41Bi-parietal Diameter

• Femur measurement– Only long bone measured routinely– Fetal age assessment when head cannot be utilized

for Bi-parietal diameter

• Multiple Fetal growth parameters– Single parameter increases variability in predicting

fetal age in 3rd trimester– Variability reduction through parameter combination

42

Fetal Age Estimation in 2nd & 3rd Trimester

43

Conclusion

• Fetal age estimation is fundamental to obstetric care

• Ultrasound is a reliable method for establishing the length of pregnancy and in this way can improve obstetric care

44

45

Thank You

Q & A

46

47