Ultrasound Evaluation During the First Trimester of Pregnancy

Ultrasound
Evaluation During the First
Trimester of Pregnancy
W Bruce Clark, M.D.




Vaginal ultrasound is usually superior to
abdominal scanning


Resolution is superior because
The transducer tip is closer to the pregnancy
 This allows a higher frequency transducer




The exception being nuchal translucency


More freedom of movement on the anterior
abdominal wall


Gestational Sac





First ultrasound sign of pregnancy
At 4 weeks 1 day to 4 weeks 2 days 2-3 mm
At 5 weeks 5mm, can be seen abdominally
Beware of the pseudo sac


5 week sac


Yolk Sac


Transvaginal




Appears at 5 to 5.5
weeks
Mean Sac Diameter
(MSD) 5mm to 8mm



Transabdominal


Appears at 7 weeks



Mean Sac Diameter
(MSD) 20mm

Maximal Diameter 5-6mm at Crown Rump Length (CRL)
of 30-45mm
Visualization of Yolk Sac confirms Gestational Sac rather than a
Pseudo Sac


6 week with yolk sac


Cardiac Activity


Transvaginal




Earliest seen at 34
days, CRL 1.6 mm
Should be seen at 6.06.5 weeks, CRL 4 to
5mm, or MSD 13 to
18mm



Transabdominal


Should be seen at 8
weeks, MSD 25mm


First Trimester


Gestational Age


Best predicted by the Crown Rump
Measurement


Signs of First Trimester Pregnancy
Failure







Sac with no embryo
Embryo ≥ 4 mm with no FH
Small sac size
First trimester bradycardia

Yolk sac too big, irregular, or calcified
Slow embryo growth


Ultrasound Findings of an Abnormal
Sac



MSD >8 mm without yolk sac
MSD > 16 mm without embryo


Using HCG values to evaluate
abnormalities of pregnancy




Blood 5µ/ ml ~ 3 or 4 days
Urine 50µ/ ml ~ 10 days
Ultrasound 1,000-1,500µ/ml ~18 – 20
days
(gestational sac)


First trimester fetal abnormalities



Fetal Abnormalities
Nuchal translucency








ULTRASOUND IN PRIVATE
PRACTICE
W. Bruce Clark, M.D.


First Trimester


Gestational Age


Crown Rump Measurement



First Trimester Ultrasound


Twins/Multiples




Zygosity
Membrane Status



Gestational Age



Likelihood of Spontaneous Abortion



Signs of First Trimester Pregnancy
Failure







Sac with no embryo
Embryo ≥ 4 mm with no FH
Small sac size
First trimester bradycardia
Yolk sac too big, irregular, or calcified
Slow embryo growth