Dating Scans During Pregnancy

A dating scan is an ultrasound performed to learn the age of the pregnancy. If you or your doctor/midwife is unsure of the date of your last menstrual cycle, if you have had any bleeding, or you are unsure of when you conceived, you will receive a dating sonogram.

This ultrasound will show you exactly how far along you are, and will show you your baby as early as 4 weeks and 3 days along! (But don’t panic because some pregnancies cannot be seen until 5 weeks.) 

You will see the beginnings of a gestational sac, but no heartbeat or further fetal development yet at this stage. An embryo and fetal heartbeat can be detected as early as 6 weeks and 3 days but may not be picked up until further along. 

You will also know the location of your pregnancy. If there is a chance that it is ectopic, you will find out now.

At this stage of pregnancy, the dating scan will be done trans-vaginally, meaning the ultrasound wand will be inserted into the vagina to see the pregnancy.

A dating scan can determine the number of gestational sacs present (which may decrease by the end of the 1^st trimester, if there is more than one). Your cervix, uterus position, and ovaries will also be seen, and you will learn if there is any visible clotting or fibroids.

A sonogram done before 9 weeks will be the most accurate to use for dating the pregnancy. As the baby begins growing at a quicker rate, it is more difficult to pinpoint an exact age.

What Can Be Seen During a Dating Scan

At 5.5 weeks gestation, a tiny sac can be seen in the uterus, but the baby and heartbeat may not be detected yet. 5.5 weeks gestation means five and a half weeks from the first day of the last menstrual period, which is usually about 3.5 weeks from the date of conception.  (confusing, isn’t it?)

By 6 to 7 weeks gestation, the fetus is clearly seen on trans-vaginal ultrasound and the heartbeat can be seen (~90 to 110 beats per minute if under 6 to 7 weeks, then the heart rate speeds up to ~110 to 200 beats per minute as the baby matures).

By 8 weeks gestation the baby and its heartbeat can be detected relatively easily with trans-abdominal and trans-vaginal examination. (This is assuming that the pregnancy is at this stage of development. Sometimes a trans-vaginal examination shows that your pregnancy is less advanced than expected.)

Not everyone receives an early ultrasound, but if you do, enjoy the first glimpse of your little miracle and capture the moment with a photo and recorded heartbeat (if possible). You will be able to hear the difference in heartrate throughout your pregnancy!