During your last trimester, your health care provider might request an ultrasound for several reasons. Some providers routinely ask for a third trimester ultrasound, while others might only order an examination if there is a specific concern.
This list includes some of the common reasons to perform an ultrasound at this point in your pregnancy:
American Institute of Ultrasound in Medicine - AIUM.org
- Evaluation of fetal growth. The sonographer will measure certain parts of your unborn baby's body to confirm that he's growing properly.
- Vaginal bleeding; abdominal or pelvic pain. An ultrasound might indicate reasons for bloody discharge or aches.
- Cervical insufficiency. A sonographer will perform a careful evaluation of the cervix to make sure it has not begun to efface (shorten) or dilate as a result of the heavier baby pushing down on the cervix.
- Determination of fetal presentation. Through the ultrasound, the sonographer can confirm whether the unborn baby is in the proper position for birth -- head down toward the pelvis.
- Evaluation of fetal well-being. During an ultrasound examination, the sonographer will look to see that the baby is moving.
- Premature rupture of membranes or premature labor. If you are experiencing preterm labor pains, an ultrasound examination can confirm that the cervix is effacing or look for other signs your body is readying for birth.
- Placenta previa. If previous ultrasounds have indicated that you have placenta previa, or if your provider suspects this condition, an ultrasound examination will confirm that the placenta is still in position over the cervical opening.
Incompetent cervix: According to the American Pregnancy Association, an incomplete or weakened cervix may occur as the baby grows and gets heavier, pressing against the cervix. This pressure may cause the cervix to begin opening before Baby is ready to be born. This condition may lead to a miscarriage or premature delivery (however, this complication occurs in only about 1 out of 100 pregnancies).
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Images courtesy of the American Institute of Ultrasound in Medicine (AIUM.org).