Obstetric dating scan
The conducting gel is non-staining but may feel slightly cold and wet.There is no sensation at all from the ultrasound waves.At 5-8 weeks a bradycardia (less than 90 bpm) is associated with a high risk of miscarriage.Many women do not ovulate at around day 14, so findings after a single scan should always be interpreted with caution.For example, if another scan done 6 or 8 weeks later says that one should have a new due date which is further away, one should not normally change the date but should rather interpret the finding as that the baby is not growing at the expected rate.b) The Biparietal diameter (BPD) The diameter between the 2 sides of the head. It increases from about 2.4 cm at 13 weeks to about 9.5 cm at term.Repetitive arrays of ultrasound beams scan the fetus in thin slices and are reflected back onto the same transducer.
Ultrasound can also very importantly confirm the site of the pregnancy is within the cavity of the uterus. A visible heartbeat could be seen and detectable by pulsed doppler ultrasound by about 6 weeks and is usually clearly depictable by 7 weeks.
A full bladder is often required for the procedure when abdominal scanning is done in early pregnency.
There may be some discomfort from pressure on the full bladder.
In such cases, it is reasonable to repeat the ultrasound scan in 7-10 days to avoid any error.
The timing of a positive pregnancy test may also be helpful in this regard to assess the possible dates of conception.