This document discusses the role and components of first trimester ultrasounds. It begins by providing background on the history and development of ultrasound technology. It then describes the mechanics of ultrasounds and their safety. The document outlines the standard exam components including gestational sac, yolk sac, fetal pole, cardiac activity and crown rump length. It discusses the uses of first trimester ultrasounds such as dating the pregnancy and screening for abnormalities. The document also covers topics like failed pregnancies, abortion, invasive procedures, ectopic pregnancies, molar pregnancies, nuchal translucency screening, and various fetal abnormalities.

1. ROLE OF FIRST TRIMESTER
ULTRASONOGRAPHY
Presented by :Dr. JYOTI BAGHEL
Junior Resident, OBGY
JIPMER

2. Introduction
 Integral part of obstetrics today
 First developed by Prof.Langevin to detect submarines during I-WW
 Previously known as SONAR(Sound navigation and ranging)
 Oceanographic studies
 Sir Ian Donald first to demonstrate the use in obstetrics(1950s)
 Robinson measured CRL and EDD

3. Mechanics Inverse piezo electric effect
 Electric current applied to piezoelectric crystals -Ultra sound wave produced
 Transducer transmits and receives USG waves reflected from tissues.
 TAS – 2 – 6.5 MHz
 TVS – 5 – 15 MHz
 Real time grey scale B mode study (2 D study)
 M mode – Motion mode in B mode; for cardiac motion to assess heart rate
and rhythm
 3D – 3 dimensional image through a special computer software.
 4D – Real time 3D ultra sound
 Doppler and power Doppler.

4. Safety:
 Use of sound waves, not a form of ionizing radiation.
 Many international bodies recommends, including ISUOG,that use of B
mode and M mode prenatal ultrasonography,due to its limited acoustic
output ,appears to be safe for all stages of pregnancy.
 Energy exposure from ultrasonography has been arbitrarily limited to
94 mW/cm2
(US FDA) (ref: ACOG Committee Guidelines Number
299, September 2004)
 No contraindications to ultrasound procedure
 ALARA Principle(As low as reasonably achievable ) principle

5. COMPONENTS OF STANDARD USG
EXAMINATION

6.  Ideally before 14 weeks.
 4-9 weeks – early first trimester scan
 10-14 weeks – late first trimester scan
USES :
 In early pregnancy, it is important to:
 Confirm viability
 to assign a gestational age accurately
 Accurate dating - reduces the need for intervention for post-maturity
First trimester scan:

7.  To determine whether early pregnancy has a normal appearance, and signs
of viability
 fetal number, and in multiple pregnancies the chorionicity/amnionicity
 detection of gross fetal abnormalities
 To evaluate maternal symptoms such as pain or bleeding
 To evaluate uterine contents before termination of pregnancy
 To guide diagnostic and therapeutic procedures
USES conti..

8. Fetal structures-timing
 Comet sign – choriodecidual reaction and vascularity
before G sac becomes visible
 Gestational sac – 4-5 weeks
 Yolk sac – 5-6 weeks
 Fetal pole – 6-7 weeks
 Cardiac activity - 6-7 weeks

9. Gestational sac
 Gestational sac – first seen by
 4 weeks+ 1-3 days TVS wen the g sac is 2-3mm
 5 weeks by TAS
 Quantified by calculating Mean sac diameter (MSD) , mean
of three diameters , inner wall margin to inner wall margin in
three planes perpendicular to each other.

10. An early G sac 4 mm in diameter

11. Mean Sac Diameter

12. Double decidual sac sign
 As the mean gest sac diameter becomes 10mm ,double
decidual sac sign appears.

13. Yolk sac
 1st
structure to appear with in G sac
 TVS - Earliest when MSD – 5mm and should
always by MSD of 8mm
 TAS – MSD of 20mm

15. Embryonic disc

16. Image showing the developing fetus,yolk sac within the G sac.CRL of 4mm
corresponding to 6.1 weeks

17. Crown rump length
 Can be carried out transabominally or transvaginally.
 Gestational age from 5 weeks 4 days to 13 weeks – crown rump length.
 Crown rump length at 8 to 12 weeks - most accurate method to date pregnancy
 Predict EDD to within 5 days (2 SD)
 CRL increases 1mm per day
 Measuring CRL – Midline sagittal section of the whole embryo or fetus should be
obtained.
 Fetus should be in a neutral position (i.e neither flexed nor hyperextended)

19. 5wk+6d,7wk+4d,9wk+1d

20. `
 6.2 weeks

22. Cardiac activity
Visible as early as – 34 days of GA or embryonic legth of 1.6
mm
Definitely evident by the time embryo is 4-5mm(6 weeks)
Heart rate around 100bpm initially, then 130-159bpm by
8weeks and plateaus at 137-144bpm after 9weeks

24. Signs of failed pregnancy
 G sac >16mm without embryo
 G sac >8mm without yolk sac
 Large yolk sac > 10 mm or small sac
 Calcified or echogenic yolk sac
 Double yolk sac
 Pulse less embryo CRL >= 5mm
 Choriodecidual hemorrhage

26. ABORTION
 First trimester ultrasound is recommended for assessmentof threatened abortion
to document fetal viability
 Termination of pregnancy spontaneous or induced before the period of viability
 Presentation –variable amounts of bleeding PV with or without pain
 Fetal viability - confirms the presence of an embryo with cardiac activity at the
time of examination
 Recommended in - incomplete abortion to identify retained products of
conception
 Not recommended to investigate an inevitable abortion

27. Multiple gestation

28. T sign in monochorionic diamniotic twin

31. INVASIVE DIAGNOSTIC OR THERAPEUTIC
PROCEDURES
• Chorionic villus sampling (CVS) and amniocentesis – to be
done under continuous ultrasound guidance.
• Success depends on - reliable placental localization.
• Selective reduction in multifetal pregnancies

32. ECTOPIC PREGNANCY
Lavanya
Positive predictive value of 100% and a negative predictive value of
92% in women with a clinical suspicion of an ectopic pregnancy.
In combination with β-human chorionic gonadotropin - 96% of
ectopic pregnancies with a specificity of 100%.
If the β-hCG is at or above the discriminatory zone, AND no IUP can
be identified, the pregnancy may be ectopic
Ultra sound features :
Visualization of extra uterine G sac
Non specific, variably vascular, variably tender adnexal mass

33. ECTOPIC PREGNANCY

34. Molar pregnancy

35. Molar pregnancy

36. partial mole

37. NUCHAL TRANSLUCENCY
• At 10 to 13 weeks + 6 days (11–14 week scan)
• CRL from 45 mm to 84 mm,
• sonolucent area in the posterior fetal neck between the
soft tissues of the neck and skin
• quantify the risk of Down syndrome, trisomy 21, 18
and13,certain other chromosomal or developmental
abnormalities, and numerous genetic syndromes
• for chromosomally normal fetuses with increased nuchal
Translucency- higher risk of congenital heart disease

38. NUCHAL TRANSLUCENCY

39. Cystic hygroma

40. Fetal abnormalities
 Neural tube defects-anencephaly
 Cranial and spinal cord defects
 Facial clefts
 Gastroscisis/omphalocele
 polydactyly

41. Gastroschisis

42. holoprosencephaly

43. anencephaly