Week 6 - Gestational Age (Fetal age 4 weeks)
5 ½ to 6 ½ weeks is usually a very good time to detect either a fetal pole or even a fetal heart
beat by vaginal ultrasound. The fetal pole is the first visible sign of a developing embryo. This pole structure
actually has some curve to it with the embryo’s head at one end and what looks like a tail at the other end. The
fetal pole now allows for crown to rump measurements (CRL) to be taken, so that pregnancy dating can be a bit more
accurate. The fetal pole may be seen at a crown-rump length (CRL) of 2-4mm, and the heartbeat may be seen as a
regular flutter when the CRL has reached 5mm.
If a vaginal ultrasound is done and no fetal pole or cardiac activity is seen, another
ultrasound scan should be done in 3-7 days. Due to the fact that pregnancy dating can be wrong, it would be much
too early at this point to make a clear diagnosis on the outcome of the pregnancy.
Week 7 - Gestational Age (Fetal Age 5 weeks)
Generally from 6 ½ -7 weeks is the time when a heartbeat can be detected and viability can be
assessed. A normal heartbeat at 6-7 weeks would be 90-110 beats per minute. The presence of an embryonic heartbeat
is an assuring sign of the health of the pregnancy. Once a heartbeat is detected, the chance of the pregnancy
continuing ranges from 70-90% dependent on what type of ultrasound is used. If the embryo is less than 5mm CRL, it
is possible for it to be healthy without showing a heartbeat, though a follow up scan in 5-7 days should show
If your doctor is concerned about miscarriage, blighted ovum, or ectopic pregnancy, the
gestational sac and fetal pole (if visible) will be measured to determine what type of development should be seen.
The guideline is that if the gestational sac measures >16-18mm with no fetal pole or the fetal pole measures 5mm
with no heartbeat (by vaginal ultrasound), then a diagnosis of miscarriage or blighted ovum is made. If the fetal
pole is too small to take an accurate measurement, then a repeat scan should be done in 3-5 days. If there is
absence of a fetal pole, then further testing should be done to rule out the possibility of an ectopic