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selective intrauterine growth restriction.Twins who share a placenta are called monochorionic twins and are always identical. If twins are visible at your 12-week ultrasound, the sonographer will perform a chorionicity scan to determine if the twins share a placenta. If you have a more complicated pregnancy, your doctor may recommend more ultrasounds. In a standard pregnancy, this includes the 12-week ultrasound and the 20-week anatomy scan. However, the American College of Obstetrics and Gynecologists (ACOG) recommends sticking only to those ultrasounds that are medically required. There’s no current research to indicate that ultrasounds are harmful to a developing baby.
![twins 4d ultrasound twins 4d ultrasound](http://i1.ytimg.com/vi/SdC07YuIgpM/hqdefault.jpg)
Ultrasounds rely on soundwaves and don’t use radiation like X-rays. It shouldn’t hurt - but depending on how long you’ve been holding your pee or asked to stay in certain positions, you may need to request a minute to shift around and get comfortable again! The exam should take about 30 to 45 minutes, depending on the position of your baby. They may also take a short recording of your baby’s heartbeat. Then, they’ll use a wand on this area to project a picture of your organs onto a screen. You’ll lie back on the exam table, and an ultrasound technician will apply a clear gel across your lower belly. (In occasional cases, an internal - known as transvaginal - scan may be necessary if the external scan can’t produce a clear image.) The 12-week ultrasound is usually an external scan. What should you expect at your appointment?