The results of ultrasound testing provide you and your health care provider with critical information about you and your baby. The Society of Obstetricians and Gynaecologists of Canada recommends that all women have two ultrasounds: See below for descriptions of the information gathered from these two types of ultrasounds. Ultrasound uses high-frequency sound waves to create images of the inside of the body.
Prenatal Ultrasound Scans
First Trimester / Dating Ultrasound | Advanced Women's Imaging
For many women, especially after 8 weeks gestation, sufficient information about the baby may be obtained with transabdominal ultrasound only. However, in the early pregnancy, the developing embryo is very small at 6 weeks gestation, the baby is only mm long and a transvaginal ultrasound may be required to get a better image of the baby. Transvaginal ultrasound is safe and commonly performed during all stages of pregnancy, including the first trimester. It will not harm you or your baby.
First Trimester / Dating Ultrasound
Your first ultrasound scan should be performed in your first trimester of pregnancy. This can be seen as early as 5 to 6 weeks of pregnancy. Visualising the pregnancy in the womb is reassuring, because it confirms that it is in the right location. Sometimes, your doctor may use a vaginal probe for the scan when your pregnancy is about 5 to 6 weeks. Be assured that vaginal scanning is safe and will not harm your pregnancy in any way.
A dating scan is an ultrasound examination which is performed in order to establish the gestational age of the pregnancy. Most dating scans are done with a trans-abdominal transducer and a fullish bladder. If the pregnancy is very early the gestation sac and fetus will not be big enough to see, so the transvaginal approach will give better pictures. Dating scans are usually recommended if there is doubt about the validity of the last menstrual period. By 6 to 7 weeks gestation the fetus is clearly seen on trans-vaginal ultrasound and the heart beat can be seen at this early stage 90 to beats per minute under 6 to 7 weeks, then to beats per minute as the baby matures.