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Viability and Dating Scan

Using both clinical information (from the date of your last period or BhCG hormone levels discovered via a blood test) and information obtained with the ultrasound examination, we hope to be able to:

  • Confirm a pregnancy
  • Confirm a normal intrauterine location when the BhCG hormone levels are greater than 1000 IUs (usually after six weeks)
  • Confirm viability by demonstrating the presence of fetal heart motion (embryo must be greater than 5mm – 7mm long)
  • Determine the number of babies present (single, twins, triplets, etc.)
  • If twins/ multiple pregnancy, then determine if identical/non-identical
  • Calculate the ultrasound expected date of delivery (US EDC)
  • Look for a cause of bleeding in early pregnancy and confirm viability

Each ultrasound examination is a snapshot in time of your pregnancy, and in the first six weeks, ultrasound may be nonspecific and require correlation with either an additional follow-up scan and/or a repeat blood test of your BhCG hormone level.

All early scans will include a scan across your pelvis with a full bladder (trans abdominal scan) and an internal scan (transvaginal/endovaginal scan). These internal scans do not harm you or the pregnancy and are standard practice around the world.

The ultrasound appearance changes throughout the pregnancy. On transvaginal scans at five weeks’ gestation, only a gestational sac will be seen. As the pregnancy grows and the mean sac diameter reaches 8-10 mm, the yolk sac will then become visible. After this, a small embryo becomes apparent at around six weeks. When the embryo is more than 5mm – 7mm, the heartbeat should be visible.

At up to 14 weeks’ gestation, the dating of the pregnancy is achieved by measuring from the top of the fetus’ head to the bottom (the crown rump length). The due date is calculated from this measurement.