You'll be hopping and skipping to this doctor's appointment -- most women agree that an ultrasound is the one prenatal test they enjoy. An ultrasound is a painless diagnostic test that relies on sound waves, and most women will have at least one during pregnancy. Your first ultrasound will typically be done between 18 and 20 weeks, but you may have one before 12 weeks to confirm your due date. You may also have an earlier ultrasound -- or more than one -- if yours is a high-risk pregnancy, if you have any pain or bleeding, if you have a history of having children with birth defects, or if another prenatal test or exam shows something abnormal. In addition, you'll have additional ultrasounds if you have a chronic illness such as diabetes or a history of ovarian cysts or fibroids.
An ultrasound usually can be done in your practitioner's office or your local hospital. You will be asked to lie on your back while a technician rubs a warm gel on your belly. The gel allows the transducer (a handheld device that looks like a microphone) to slide more easily over your belly and improves the transmission of sound waves into your body. The sound waves bounce off various surfaces within your body -- including your baby -- as vibrations. The echoes are translated into electrical signals that are projected as pictures onto a monitor for viewing. An abdominal ultrasound poses no risk to you or your baby. In fact, there are many benefits to checking on your baby's development during pregnancy.
If you need an ultrasound early in pregnancy, it may be necessary to use a vaginal probe (a transducer placed in the vagina). This allows the technologist to view your uterus through the cervix. This method may also be used later in pregnancy to locate your placenta if it's over the cervix or to measure the length of the cervix. Vaginal probes may cause a sensation of pressure but shouldn't adversely affect your pregnancy.
Your ultrasound in the 1st trimester can show your baby's heart rate, umbilical cord, and size, as well as the placenta. It will also tell you if you have one, two, or three babies. An ultrasound in the 2nd trimester (around 18 weeks) can show details of the fetal head, face, spine, heart, abdomen, and limbs, in addition to the placenta.
The examiner is looking for physical characteristics that might indicate any abnormality. Ultrasounds can't detect all birth defects, and a normal ultrasound doesn't guarantee a healthy baby. However, ultrasound is a wonderful diagnostic tool that can help ensure that your pregnancy and your baby are both on the right track.
Originally published in You & Your Baby: Pregnancy.
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