Obstetrics Location 378 South Branch Road Suite 403 Hillsborough, NJ 08844 (908) 369-0970 Obstetrical Ultrasound Prenatal ultrasound testing uses high-frequency sound waves to view images of the baby, amniotic sac, placenta, and ovaries.  Generally, two ultrasounds are done during pregnancy at approximately 12 and 20 weeks.  The 12 week ultrasound determines whether your pregnancy is singleton or twin, due date, and can detect some genetic and structural abnormalities.  This ultrasound, combined with bloodwork, is the first part of sequential screening for trisomy 18 and 21. The 20 week ultrasound is a full anatomical scan.  Multiple measurements are taken to assess the health and growth of the baby.  Assessment of the placenta and fluid is also done.   If you wish to know the gender of your baby, it can usually be determined by 20 weeks. Be sure to tell the health care provider performing the ultrasound whether or not you want to know the gender of your baby. Additional ultrasounds are sometimes necessary.  These include determination of fetal size, assessment of fetal health, and other specific testing ordered when necessary. Obstetrics-Home What To Expect Your First Prenatal Visit Prenatal Testing Ultrasound Obstetrics FAQs Medications in Pregnancy