Ultrasound Evaluation During the First Trimester of Pregnancy

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Ultrasound Evaluation During the First Trimester
of Pregnancy

• W Bruce Clark, M.D.

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• 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

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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

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5 week sac
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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
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6 week with yolk sac
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Cardiac Activity

• Transvaginal
• Earliest seen at 34 days, CRL 1.6 mm
• Should be seen at 6.0-6.5 weeks, CRL 4 to 5mm, or
  MSD 13 to 18mm

• Transabdominal
• Should be seen at 8 weeks, MSD 25mm

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First Trimester

• Gestational Age
• Best predicted by the Crown Rump Measurement

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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

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Ultrasound Findings of an Abnormal Sac

• MSD gt8 mm without yolk sac
• MSD gt 16 mm without embryo

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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)

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First trimester fetal abnormalities

• Fetal Abnormalities
• Nuchal translucency

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ULTRASOUND IN PRIVATE PRACTICE

• W. Bruce Clark, M.D.

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First Trimester

• Gestational Age
• Crown Rump Measurement

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First Trimester Ultrasound

• Twins/Multiples
• Zygosity
• Membrane Status
• Gestational Age
• Likelihood of Spontaneous Abortion

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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

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Ultrasound Findings of an Abnormal Sac

• MSD gt8 mm without yolk sac
• MSD gt 16 mm without embryo

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Ectopic Pregnancy
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Diagnosis 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)

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First trimester fetal abnormalities

• Fetal Abnormalities
• Nuchal translucency

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Second trimester fetal abnormalities

• Anatomical
• Chromosomal

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Markers for chromosomal abnormalities

• Short femur
• Nuchal thickness
• Pyelectasis
• Choroid plexus cyst
• Anatomical abnormalities

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Third trimester fetal well being

• Growth
• Doppler flow of umbilical arteries
• Amniotic fluid volume
• Placental grade
• Fetal breathing movements

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