Obstetrics Services

Pregnancy Dating

Your obstetrician is able to confirm and date your pregnancy with the use of an ultrasound scan. Your obstetrician will take various measurements of the gestational sac in early pregnancy and later of the fetus. Your first scan will typically take place between 11 and 13 weeks into your pregnancy. Your dating scan will also allow your doctor to check that your baby is developing properly.

Pregnancy weeks are divided into three trimesters, each one with a medical milestone for both the mother and the baby. The trimesters are as follows:

1st trimester – This is week 1-12, and the fetus starts developing the brain, spinal cord and organs, as well as the baby's heart start beating.
2nd trimester – This is week 13-27, and this is when the baby starts moving, kicking and punching inside the uterus.
3rd trimester – This is week 28-40, and the baby begins to sense light as well as open and close their eyes. The bones have formed.

Your dating scan will typically take no more than half an hour, and you will be asked to arrive with a full bladder. Gel will be placed on your stomach, and a hand-held scanning device will be moved over your skin so that an image can be displayed on a screen. For more information on ultrasound scanning during pregnancy, click here.

As well as ultrasound scanning, your obstetrician will also take into account your last menstrual period to calculate your due date. Generally, the duration of a pregnancy is forty weeks from the first day of your last menstrual period. The ultrasound can be done transabdominally (on the skin of the abdomen and preferably with a full bladder), or it can be done transvaginally (inserting a transducer in the vagina and is done with an empty bladder).

Your obstetrician will also conduct a physical exam to support the date revealed by your ultrasound scan. This will include a pelvic exam as the uterus moves according to the stage of pregnancy.