The purpose of performing an obstetric ultrasound is to provide a safe, non-invasive, and accurate method to clinically evaluate the pregnant uterus and fetus, right from the confirmation of a viable (alive) pregnancy to throughout the woman’s pregnancy.
Ultrasound imaging is a type of radiological assessment, also called an ultrasound scan or ultrasound sonography (USG) or sonography. It consists of a small probe called a transducer that is placed directly over the skin. A gel is applied over the skin before placing the transducer. High-frequency sound waves generated in the device travel from the transducer through the gel into the body. Sound is absorbed by the tissues and reflected to the transducer. The sound waves are converted to electrical impulses that are interpreted as black and white images.
Why is an obstetrics ultrasound done?
Obstetric ultrasound is usually performed every three to four weeks to monitor the fetus and pregnant uterus throughout pregnancy.
First-trimester obstetric ultrasound:
An ultrasound is first performed to confirm a viable pregnancy. It may be performed either trans-abdominal (the transducer is placed over the abdomen) or trans-vaginally (the transducer is narrow and placed in the vagina). Sometimes, both may be done simultaneously. It is ideally performed before 13-14 weeks of pregnancy. A first-trimester ultrasound examination can help diagnose a miscarriage early and the presence of multifetal gestations (multiple fetuses such as twins or triplets). A first-trimester ultrasound also helps to evaluate the mother’s reproductive system to detect anatomical abnormalities and pathologies.
Second- and third-trimester obstetric ultrasound:
Second- and third-trimester ultrasounds help to assess fetal growth and anatomy. An obstetric ultrasound examination may also include evaluation of the fetal position, amniotic fluid volume around the fetus in the uterus, location of the placenta, fetus’s cardiac activity, the fetal spine, and fetal anomalies.
If fetal anomalies are detected between 18 and 20 weeks of pregnancy, termination of pregnancy may still be an option. Motioning the fetus with the help of ultrasound helps to monitor fetal health, determine the mode of delivery, and calculate the estimated fetal weight and amniotic fluid. Fetal growth evaluations are typically performed every three to four weeks.
How do you prepare for an obstetric ultrasound?
The preparation required for a trans-abdominal or transvaginal ultrasound is minimal. Some doctors advise their patients to arrive with a full bladder for an ultrasound, especially when an obstetric ultrasound is performed after 18 weeks of pregnancy. If a transvaginal ultrasound is to be performed, the patient is asked to void (empty the bladder by urination) just before the ultrasound. This reduces discomfort and collapses the bladder for better visualization of the pelvic organs. Ultrasound transducers are not disposable; hence, it is advisable for patients to visit a center that follows proper hygiene protocols because the transducers require proper cleaning before and after each patient’s use to avoid infection. Trans-abdominal ultrasound transducers are typically cleaned with disposable antiseptic wipes, and the clean transducer may be applied directly to the patient’s skin. Trans-vaginal transducers are usually covered with a disposal cover during the ultrasound. After the ultrasound, the patient can go home right after and return to their usual activities.
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