The document provides information on normal sonological findings in the first trimester of pregnancy. It discusses the visualization of structures like the gestational sac, yolk sac, fetal pole, amniotic membrane, and fetal heart during transvaginal ultrasounds between 5-13 weeks of gestation. Key milestones include the gestational sac being visible at 5 weeks, yolk sac at 5.5 weeks, fetal pole and heart at 6 weeks, and detailed anatomy becoming apparent by 12 weeks. Abnormal appearances that could indicate problems are also described.

1. NORMAL SONOLOGICAL
FINDING IN FRIST
TRIMESTER
DR.VIPIN KUMAR PRIYADARSHI
PCPNDT BATCH FEB 2024
SNMC AGRA

2. INTRODUCTION
THE FIRST TRIMESTER OF PREGNANCY CONSISTS OF THE FIRST 12-13
WEEKS,CALCULATED AS BEGINNING ON THE FIRST DATE OF THE LAST MENSTRUAL
PERIOD.
DURING THE FIRST TRIMESTER TRANSVAGINAL ULTRASONOGRAPHY IS THE
IMAGING MODALITY OF CHOICE FOR BOTH DIAGNOSIS AND IMAGING FOLLOW-UP.
THE INITIAL DIAGNOSIS OF PREGNANCY IS USUALLY MADE BY IDENTIFYING THE
PRESENCE OF SERUM BETA-HCG.
IN THE FIRST TRIMESTER ,PELVIC ULTRASOUND IS EMPLOYED TO ESTABLISH THE
PRESENCE OR ABSENCE OF AN INTRAUTERINE GESTATIONAL SAC AND TO
EVALUATE THE VIABILITY OF THE PREGNANCY
IT CAN BE USED TO EVALUATE ECTOPIC PREGNANCY AND OTHER PREGNANCY
RELATED COMPLICATIONS.

3. OBJECTIVES
CONFIRMATION OF THE PRESENCE OF AN INTRAUTERINE PREGNANCY.
ESTIMATION OF GESTATIONAL AGE.
DIAGNOSIS OR EVALUATION OF MULTIPLE GESTATIONS.
CONFIRMATION OF CARDIAC ACTIVITY.
EVALUATION OF A SUSPECTED ECTOPIC PREGNANCY.
MEASURING THE NUCHAL TRANSLUCENCY.
EVALUATION OF SUSPECTED HYDATIDIFORM MOLE.
ASSESSING FOR CERTAIN FETAL ANOMALY,SUCH AS ANENCEPHALY IN HIGH RISK
PREGNANCY.
DETECTION OF SIGN OF EARLY PREGNANCY FAILURE.

4. TRANSVAGINAL ULTRASONOGRAPHY(TVS)
THE TVS IS THE STANDARD METHOD OF EXAMINING FIRST TRIMESTER PREGNANCY.
THE TRANSVAGINAL TRANSDUCER HAVE HIGHER RESOLUTION,AND ARE POSITIONED
CLOSER TO THE UTERUS,THE GESTATIONAL SAC AND PELVIC ORGANS.
STEPS
THE PATIENT IS INFORMED AND CONSENTED(ORALLY).
THE PATIENT EMPTIED HER BLADDER AND IS PLACED IN A DORSAL LITHOTOMY
POSITION OR IN A SUPINE POSITION WITH THE BUTTOCKS ELEVATED BY A CUSHION.
COVER SHEET IS APPLIED TO PROVIDE PRIVACY AND WHEN POSSIBLE IT IS
RECOMMENDED TO HAVE A THIRD PERSON (FEMALE)PRESENT IN THE ROOM.

5. STEPS IN TVS
CHECK THAT TRANSDUCER HAS BEEN CLEANED BASED UPON RECOMMENDED
GUIDELINE.
APPLY GEL ON THE TRANSDUCER TIP,COVER WITH SINGLE USE CONDOM AND
APPLY GEL ON THE OUTSIDE OF THE CONDOM,PAYING ATTENTION NOT TO
CREATE AIR BUBBLES BELOW THE COVER.
INSERT THE TRANSDUCER GENTLY AND ANGLE IT INFERIORLY(TOWARD
RECTUM)DURING INSERTION INTO THE VAGINAL CANAL AS THIS REDUCE PATIENT
DISCOMFORT
SPEAK WITH THE PATIENT,EXPLAIN WHAT YOU ARE DOING AND ASK ABOUT
POSSIBLE DISCOMFORT.

6. Gestational sac becomes visible
(5 weeks GA)
Yolk sac becomes visible
(5.5 weeks GA)
Fetal pole and heart motion become visible
(6 weeks GA)
Embryo begins to show features and
rhombencephalon begins to
form
(between 8–10 weeks GA)
Detailed anatomy
becomes more apparent
(12 weeks GA)
Yolk sac
no longer
visualized
Amnion fuses
with chorion
(14 weeks GA)
Timeline of Early Pregnancy
8-10 weeks 12 weeks and beyond
P
a
g
e
:
3
2
o
f
8
2 P
a
g
e
:
3
2
o
f
8
2
I
M
:
3
2 I
M
:
3
2
Gestation
al Age
(GA)
5 weeks 6 weeks 7 weeks 8 weeks 9 weeks
10
weeks
11
weeks
12
weeks
13
weeks
14
weeks
Physiologic gut herniation completes
(begins at 6–8 weeks GA and completes at 12–13
weeks GA)

7. GESTATIONAL SAC
At 5-5.5 week gestation,the gestational sac become visible.
The growth rate of gestational sac is approximately 1.1 mm/day an
First become apparent on TVUS at 4.5-5 weeks,appearing as a roun
Structure located eccentrically within the echogenic decidua.
Terms such as intradecidual sac sign and double
decidual sac sign were originally used to describe
findings in the gestational sac at transabdominal US.
With the advent of transvaginal US, these signs were
found to be absent in at least 35% of gestational sacs

8. GESTATIONAL SAC (NORMAL)
US image shows a normal
gestational sac
The gestational sac should be round or oval, appear
smooth and well defined, have a decidua that is 2 mm
or greater, and be positioned in the upper uterine body.
Gestational sacs that deviate from this appearance are
suspicious for abnormal pregnancies.4
Abnormal shape Irregular margins and
shape
Associated with poor
outcomes5
Small gestational sac
Normal mean sac diameter
(MSD) should be greater than
or equal to 5 mm larger than
the crown rump length (CRL) at
less than 9 weeks
MSD less than 5 mm larger than
the CRL is associated with poor
outcomes
Thin decidual
reaction
Thin decidual
reaction with
weakly
hyperechoic sac
wall
Associated with
poor outcomes
Abnormal appearance of
gestational sac

9. YOLK SAC
The yolk sac is the next structure to appear
after the gestational sac, becoming visible at
approximately 5.5 weeks GA.
The yolk sac gradually enlarges until 10 weeks
GA, measuring up to 5–6 mm.
After 10 weeks, the yolk sac begins to shrink
until it is no longer visualized beyond 14
weeks GA

10. VARIABLE AND ABNORMAL APPEARANCES OF THE YOLK
SAC
Small yolk sacs visualized in very early pregnancy (before
expected shrinking after 10 weeks)
• Scant knowledge of outcomes
• Limited study showed a sac less than 2 mm is associated with poor
outcomes7
• Prudent to recommend close follow-up
Large yolk sac (> 5–6 mm)
• Associated with increased risk of demise8

11. VARIABLE AND ABNORMAL APPEARANCES OF THE
YOLK SAC
Absent yolk sac
Abnormal in early
pregnancy if the
embryo had been
present while the
yolk sac was
involuting
Generally
associated with
embryonic
demise9
Internal echoes within the
yolk sac
anecdotally are not
associated with poor
outcomes
Differential diagnosis:
calcified yolk sac
(calcified rather than
echogenic material in the
yolk sac),
which is associated with
failed IUP

12. YOLK SAC
• VISUALIZATION OF MULTIPLE YOLK SACS IS THE EARLIEST SIGN OF A MULTIGESTATIONAL
PREGNANCY.
• THE NUMBER OF YOLK SACS MATCHES THE NUMBER OF AMNIOTIC SACS IF THE EMBRYOS
ARE ALIVE.
• THE FIRST TRIMESTER IS THE EASIEST TIME TO DETERMINE CHORIONICITY AND
AMNIONICITY OF A MULTIGESTATIONAL PREGNANCY
Monochorionic diamniotic
US image shows a single
chorionic cavity without an
intervening membrane
(monochorionic).
US image shows two chorionic
cavities (dichorionic), which are
divided by a thick triangular-shaped
membrane (arrow). This is referred to
as the twin peak sign or lambda (λ)
sign.14
Dichorionic diamniotic
US image shows two embryos ( , ).
One chorionic cavity is visualized
(monochorionic).
One yolk sac is also identified
(monoamniotic).
2
1
2
1
Monochorionic monoamniotic

13. FETAL HEART RATE
• FETAL HEART MOTION IS USUALLY DETECTABLE AROUND 6 WEEKS GA (USUALLY
VISIBLE AS SOON AS THE EMBRYO IS DETECTABLE).
• THE LOWER LIMIT OF NORMAL FOR FETAL HEART RATE (FHR) IS 100 BEATS PER
MINUTE (BPM) (AT GA < 6.2 WEEKS) AND 120 BPM (AT GA > 6.2 WEEKS).15
• AN FHR LESS THAN OR EQUAL TO 90 BPM IN THE FIRST TRIMESTER CARRIES A DISMAL
PROGNOSIS.15
Fetal pole and heart motion become
visible
(6 weeks GA)

14. FETAL HEART RATE
• FHR IS CALCULATED BY MEASURING THE
DISTANCE FROM TROUGH TO TROUGH OF
TWO SUBSEQUENT WAVES.
• THE CURRENT GUIDELINES OF THE SOCIETY OF
RADIOLOGISTS IN ULTRASOUND (SRU) ESTABLISH
A CRL CUTOFF OF 7 MM, ABOVE WHICH ONE
SHOULD DEFINITIVELY VISUALIZE FETAL CARDIAC
ACTIVITY.
• THE ABSENCE OF A DETECTABLE HEARTBEAT
ONCE THE EMBRYO MEASURES GREATER THAN 7
MM IN LENGTH IS DIAGNOSTIC OF PREGNANCY
FAILURE .
• THE FETAL HEART RATE GRADUALLY INCREASES
WITH GESTATIONAL AGE FROM APPROXIMATELY
110 BEATS PER MINUTE (BPM) AT 6.2 WEEKS TO

15. FETAL HEART RATE
• M-MODE IS THE PREFERRED US MODE OVER COLOR AND PULSED (SPECTRAL) DOPPLER US.
• COLOR AND PULSED-WAVE DOPPLER US ARE ASSOCIATED WITH HIGHER POWER OUTPUT
(TABLE).
• ALTHOUGH THERE IS NO EVIDENCE THAT COLOR AND PULSED-WAVE DOPPLER US ARE
HARMFUL, ALL BUT BRIEF INSONATION IS NOT RECOMMENDED DURING THE EMBRYONIC
PERIOD.16
• SPECTRAL DOPPLER US SHOULD ONLY BE EMPLOYED WHEN THERE IS A CLEAR BENEFIT-RISK
ADVANTAGE AND BOTH THERMAL INDEX (TI < 1) AND EXAMINATION DURATION ARE KEPT
LOW.17

16. FETAL RHOMBENCEPHALON
• THE FETAL RHOMBENCEPHALON (WHICH FORMS
THE MEDULLA, PONS, AND CEREBELLUM)
IS VISIBLE BETWEEN 8 AND 10 WEEKS GA.
• IT APPEARS AS A ROUNDED ANECHOIC
STRUCTURE IN THE POSTERIOR BRAIN (ARROW).
THIS IS A NORMAL FINDING AND SHOULD NOT BE
MISINTERPRETED AS A CONDITION

17. ASSESSMENT OF GA
• DETERMINATION OF GA IS MORE ACCURATE THE EARLIER US IS PERFORMED.
• MSD MEASUREMENTS ARE NOT RECOMMENDED FOR ESTIMATING DUE DATE.
• CRL IS THE MOST ACCURATE METHOD TO ESTABLISH GA (UP TO AND INCLUDING 13 6/7
WEEKS OF GESTATION).
• BEYOND A CRL OF 84 MM (14 WEEKS, 0 DAYS), DATING ON THE BASIS OF CRL BECOMES LESS
ACCURATE, AND OTHER SECOND-TRIMESTER BIOMETRIC PARAMETERS SHOULD BE USED.
THESE PARAMETERS (BIPARIETAL DIAMETER, ABDOMINAL CIRCUMFERENCE, HEAD
CIRCUMFERENCE, AND FEMUR LENGTH) ARE USED TO DETERMINE THE ARITHMETIC US AGE.
• AT A GA OF 8 6/7 WEEKS OR LESS (BASED ON LAST MENSTRUAL PERIOD [LMP]), US DATING
SHOULD BE USED IF THE LMP DATING AND US DATING DIFFER BY MORE THAN 5 DAYS.
• AT A GA BETWEEN 9 0/7 WEEKS AND 13 6/7 WEEKS (ON THE BASIS OF THE LMP), US DATING
SHOULD BE USED IF THE LMP DATING AND US DATING DIFFER BY MORE THAN 7 DAYS.
• THE ESTIMATED DUE DATE (EDD), IF BASED ON US DATING, SHOULD BE BASED ON THE
EARLIEST US EXAMINATION OF A CRL MEASUREMENT. CHANGES TO THE EDD SHOULD BE
RESERVED FOR RARE CIRCUMSTANCES.

18. EMBRYO/FETAL POLE/CRL
The embryo (sometimes referred to as the fetal pole early
on) becomes apparent at 6 weeks of gestation as a relatively
featureless echogenic linear or oval structure adjacent to the
yolk
sac, initially measuring 1-2 mm in length.
At this point, the MSD is approximately 10 mm. The crown-
rump length (CRL) is the measurement between the cranial
and caudal ends of the embryo and is the most accurate
measure of the gestational age in the first trimester.
While the fetal pole begins as a featureless structure, some fetal
anatomic structures become visible as the first-trimester
progresses. The spine appears at 7-8 weeks, and the
hindbrain(rhombencephalon) is evident at 8-10 weeks .

19. AMNIOTIC MEMBRANE
The amniotic membrane becomes visible around 7 weeks,
and the CRL closely corresponds to the amniotic sac
diameter between 6.5 and 10 weeks of gestation.
After fetal urine production commences at about 10
weeks, there is a disproportionate enlargement of the
amniotic sac relative to the chorionic cavity.
The amnion and chorion fuse after the first trimester at
14-16 weeks.

20. CONCLUSION
• THE DIAGNOSTIC POSSIBILITIES FOR PREGNANT PATIENTS PRESENTING WITH
PAIN AND BLEEDING ARE BROAD.
• TVUS IS PARAMOUNT IN ITS UTILITY AS A DIAGNOSTIC TOOL FOR THESE
PATIENTS.
• WHEN USED IN COMBINATION WITH CLINICAL INFORMATION AND SERUM Β-
HCG LEVELS, IT CAN PROVIDE DIAGNOSTIC AND PROGNOSTIC INFORMATION
TO CLINICIANS REGARDING PREGNANCY CONFIRMATION AND VIABILITY, AS
WELL AS RAPID INFORMATION REGARDING LIFE-THREATENING CONDITIONS
SUCH AS ECTOPIC PREGNANCY.

21. THANK YOU