Obstetric Ultrasound Early Pregnancy

OBSTETRIC ULTRASOUND – Early Pregnancy/Dating/Viability

This examination is performed in the first trimester of pregnancy (4-12 weeks). The purpose of this examination is to assess and confirm viability of the pregnancy, including:

  • Correct location of the pregnancy (ie. Inside the uterus)
  • Number of babies
  • Presence of heart motion; and
  • Dating of the pregnancy

In the early stage of pregnancy (before 7 weeks gestation) it is usually necessary for a transvaginal ultrasound to be performed to see a gestation sac. Fetal heart activity will usually be detected at around 6 weeks gestation.

It is important at this early stage to confirm the correct location of a pregnancy. Occassionally a pregnancy may occur outside of the uterus, known as an ectopic pregnancy.

For twin or multiple pregnancies, early ultrasound examination can be important and helpful in planning management of the pregnancy.
Accurate dating of a pregnancy can be performed by measuring the crown rump length (CRL) from the head to the bottom. This is accurate to within a few days.

In some instances the time of conception may be uncertain and an ultrasound may show a pregnancy not as advanced as expected based on the dates from your last menstrual period (LMP). If this is the case, a follow-up ultrasound examination will be recommended after a short interval for re-assessment.

Should you have any questions regarding the above information or your ultrasound examination please do not hesitate to ask the Sonographer or Dr Susan Winspear.