what is obstetrics ultrasound

1. ❧
Obstetric Ultrasound
Lecture No. 1
Sir Akash John

2. ❧
❧ Obstetric ultrasonography
is the use of medical
ultrasound in pregnancy, in
which sound waves are
used to create real-time
visual images of the
developing embryo or
fetus in its mother's uterus.
Obstetric Ultrasound

3. ❧
❧ Confirmation of IU pregnancy and Viability
❧ Differentiation between IU and Ectopic Pregnancy
❧ Estimation of Gestational Age
❧ Detection of Multiple Gestational Sacs
❧ Evaluation of Fetal Growth, Weight, Presentation, anomalies, death or
suspected poly or oligohydramnios.
❧ Evaluation of Placenta and its complications
❧ Evaluation of vaginal bleeding of specific etiologies
❧ Evaluation for suspected molar pregnancies
❧ Pre-procedural for amniocentesis
Common Indications for
Obs Ultrasound

4. ❧
❧ For IUCD localization
❧ Suspected Uterine abnormalities or pelvic masses
❧ Bio-physical profile after 28weeks
❧ Adjacent to special procedures such as fetoscopy, IU
transfusion, shunt placement, in vitro fertilization, embryo
transfer and chronic villus sampling.
❧ Follow-up.

5. ❧
❧ Unsure last menstrual period
❧ Vaginal bleeding during pregnancy
❧ Uterine size not equal to expected for dates
❧ Use of ovulation-inducing drugs confirm early pregnancy
❧ Obstetric complications in a prior pregnancy: ectopic, preterm
delivery
❧ Screen for fetal anomaly: abnormal serum screens, certain drug
exposure in early pregnancy, maternal diabetes. Rh isoimmunization
❧ Postdate fetus
❧ Twins (monochorionic)
❧ Intrauterine growth restriction (IUGR)
Clinical Indications

6. ❧
❧ Viability of the fetus can be documented in presence of
vaginal bleeding in early pregnancy
❧ heartbeat could be seen and detectable by pulse Doppler
about 6 weeks (if this is observed , the probability of a
continuing pregnancy is more than 95%
❧ 5% (missed abortion, blighted ovum)
Vaginal Bleeding In Early
Pregnancy

7. ❧
❧ Fetal heart rate tends to vary with gestational age:
❧ 6 weeks 90-110 beats per minute
❧ 9 weeks 140-170 beats per minute
❧ 5-8 weeks: a bradycardia less than 90 beats per minutes is
associated with high risk of miscarriage.
❧ Many women dot not ovulate at around day 14, findings
after a single scan should always be interpreted with
caution; the diagnosis of missed abortion is usually made
by serial US scans (lack of gestational development)

8. ❧
❧ Three type of transducers are used:
❧ 1. Sector Transducer:
❧ Ideal for 1st
trimester as the access is limited
❧ 2. Linear Array Transducer:
❧ Preferably used in 2nd
and 3rd
trimester
❧ 3. Convex Transducer:
❧ Most commonly used in complete trimesters imaging.
The appropriate frequency for all transducers lie between 3 to 5
MHz. Moderately distended urinary bladder is essential for
evaluating patients in the 1st
trimester.
Equipment

9. ❧

10. ❧
❧ TV transducers usually
have frequency of 6.5
MHz which provides
better resolution.
❧ It is also more sensitive in
detection of ectopic
pregnancy and for
evaluating other
complication of early
pregnancy.
TVU (trans-vaginal
ultrasound)

11. ❧
❧ Documentation of location of gestation sac, Embryo
Identified and CRL (crown rump length) measured.
❧ Presence or absence of fetal life recorded.
❧ Fetal Cardiac motion is seen around six weeks
TrA(trans-abdominally) and 1 week prior by TVS
(trans-vaginal).
❧ Documentation of Fetal Number.
❧ Evaluation of uterus and adnexal structures.
Guidelines for First-trimester
Sonography

12. ❧
❧ In the first trimester, the initial ultrasound examination can be
performed transabdominally or transvaginally.
❧ The transabdominal (TA) ultrasound allows for a more comprehensive
overview of the uterus and adnexa, but the transvaginal (TV)
ultrasound provides superior resolution and detail.
❧ If TA ultrasound is done first and all normal landmarks are identified,
including the gestational sac, the embryo with heart motion, and the
ovaries, further evaluation with TV ultrasound is not required.
1st
Trimester

13. ❧
❧ Documentation of fetal life, number and presentation.
❧ An estimate of the amount of amniotic fluid (increased,
decreased and normal) should be reported.
❧ Record placental location and its relationship to internal os.
❧ Assess gestational age using biparietal diameter, head
circumference and femur length.
❧ Fetal anatomy should be demonstrated such as cerebral
ventricles, spine, stomach, urinary bladder, umbilical cord
insertion on the abdominal wall and kidneys and associated
anomalies.
Guidelines for 2nd
and 3rd
trimesters

14. ❧
❧ If, the gestational sac is not identified, the sac is seen
without an embryo, or the embryo is identified but no
heart motion is detected, a TV study should also be
performed.

15. ❧
❧ The yolk sac is the first structure identified by sonography in a normal
gestational sac, usually visualized around 5.5 weeks.
❧ The embryo is seen around 6 weeks.
❧ The terms gestational age, embryonic age, fetal age, and menstrual age
are often used interchangeably, referring to age of the pregnancy
calculated from the first day of onset of the last menstrual period
(LMP).
Yolk sac and Embryo

16. ❧

17. ❧
❧ The crown-rump length
(CRL) is the primary
measurement considered
when establishing
gestational age during the
first trimester and is
obtained by measuring
from the top of the fetal
head to the rump.
Crown Rump Length
(CRL)

18. ❧
❧ The assigned estimated gestational age is based on LMP if
it is similar to the predicted age by CRL (typically within
5 days during the first trimester).
❧ However, if there is a larger difference between the
estimated gestational age based on LMP and by CRL, the
CRL is used.
Gestational Age