1. OBSTETRIC ULTRASOUND TECHNIQUES FETAL AGE ESTIMATION

3. 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 women

4. 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

5. Transducer
Transmitted pulse
Received pulse
Object

6. 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

7. Common Uses of Obstetric USG cont
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

8. 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

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

10. 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

12. 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

13. 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

15. 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. 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. Application of Ultrasound in Trimesters
First Trimester
Commonly performed at 9-12 weeks
2nd and 3rd Trimester
Commonly performed at weeks

20. Obstetric USG in 1st Trimester
Identification of Gestational sac and Embryo
First trimester fetus and yolk sac

21. Obstetric USG in 1st Trimester cont
Recording the presence or absence of fetal life
Embryo 4 weeks

22. Obstetric USG in 1st Trimester cont
Identification and documenting the fetal number
Two gestational sacs, each containing a yolk sac

23. Obstetric USG in 1st Trimester cont
Evaluation of Uterus and Adnexal structures
Uterus and cervical plug

24. Obstetric USG in 1st Trimester cont
Measurement of Nuchal Translucency
Nuchal Translucency

25. Triplet with sub-chorionic bleeding

27. Twin pregnancy
28 mm CRL in 10 weeks

28. Obstetric USG in 2nd and 3rd Trimester
Fetal life, number and presentation
Amount of amniotic fluid

29. Obstetric USG in 2nd and 3rd Trimester cont
Record Placental localization
Establishment of fetal age and growth by fetal biometry including
Bi-parietal Diameter
Head Circumference
Femur Length
Abdominal Circumference

30. 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

31. Fetal Cardiac Structure

32. Fetal Age Estimation
Assessment of gestational age is fundamental to obstetric care
Ultrasound is a reliable method for establishing the length of pregnancy

33. 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

35. Fetal Age Estimation in 2nd & 3rd Trimester
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

36. Fetal Age Estimation in 2nd & 3rd Trimester
Bi-parietal diameter and head circumference measurements

37. Bi-parietal Diameter

38. Fetal Age Estimation in 2nd & 3rd Trimester
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