In a normal pregnancy, typically a person will have two ultrasounds. One is normally done in the first trimester and is used to determine a due date and/or for prenatal screening. The second is usually done between 18-22 weeks and is used to evaluate the anatomy of the baby to make sure everything is developing normally, and to check the location of the placenta. The baby’s sex can sometimes be determined at this ultrasound if the baby is positioned well, although ultrasounds are not ordered solely for the determination of sex.
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u may have more ultrasounds than this depending on the circumstances. Sometimes all of the anatomy cannot be seen well because the baby’s position at the time, in which case you may have another ultrasound at a later date. Sometimes the placenta location requires followup ultrasounds. If there are concerns about the baby’s growth an ultrasound might be ordered to estimate the size of the baby. If you go past your due date, an ultrasound is usually done while you are awaiting the onset of labour to make sure everything is still going well.
Although obstetrical ultrasound is considered safe, it is recommended that ultrasound be used only for medical reasons. Ultrasounds are therefore not ordered for the sole purpose of determining sex, and the use of 3D ultrasounds for non-medical indications is discouraged.
*SOGC statement of ultrasound safety