The first ultrasound can be done anytime within the first trimester of pregnancy. Usually, ultrasounds during pregnancy will be done externally with a transabdominal probe with gel; however, earlier on in the first trimester, it may be necessary to complete the ultrasound transvaginally. During a transvaginal ultrasound, a probe covered with a plastic sheet and gel, is placed in the vagina to allow for early visualization of the baby.

If your ultrasound is performed between 5- and 6-weeks’ gestation, you will likely only be able to see the gestational and yolk sacs. The gestational sac is the sac in which your baby is growing, and it allows your doctor or midwife to confirm your pregnancy, even though the baby may not be identifiable just yet. If your ultrasound is completed between weeks 6 and 7, your baby is measuring nearly 9 mm in length and measured in crown-rump-length (CRL); typically, a heartbeat is seen within this timeframe. Ultrasounds completed during 8 to 11 weeks will show your growing baby, which during this time has identifiable features such as the body, head, arms, and legs, and is moving quite readily within the gestational sac.

The purposes of the first trimester ultrasound are to evaluate the size of the baby and characteristics of the baby’s gestational sac, such as size and appearance, to detect the heartbeat, to correctly date your pregnancy to determine the expected date of delivery, to ensure the baby is growing within the uterus and not in another structure like the fallopian tube, to evaluate the presence of multiple babies, to identify any ovaries and uterus abnormalities.