Color Doppler ultrasound is performed in pregnancy to assess blood flow in the fetus, umbilical cord, placenta and fetal heart. It’s indicated in high‑risk situations—suspected fetal growth restriction, preeclampsia, abnormal fetal monitoring, multiple pregnancy, suspected fetal anemia or abnormal anatomy. Typically used from the second trimester onward (often after 20 weeks) and repeated in the third trimester for surveillance.

A color Doppler ultrasound is generally painless and non-invasive. A technician applies warm gel and moves a handheld probe across the skin; you may feel mild pressure or vibration, especially if the area is tender, but it should not cause sharp pain. The test uses sound waves (no radiation) and usually takes 15–45 minutes. Any discomfort typically ends right after the exam.

Doppler (fetal heartbeat) cannot reliably determine a baby’s gender. Gender is usually identified by ultrasound visualization of the genitalia, most accurate at 18 to 20 weeks; "nub" assessments at 12 to 14 weeks are less reliable. Accuracy depends on gestational age, fetal position, sonographer skill and equipment. Definitive prenatal sex determination requires genetic testing (cell‑free DNA, CVS, amniocentesis).

The best time for a color Doppler depends on the indication: perform immediately for suspected DVT or acute vascular problems; during the routine anatomy scan (≈18–22 weeks) or later in pregnancy for growth/placental concerns; schedule abdominal Doppler after 6–8 hours fasting to reduce bowel gas. For other vascular or cardiac issues, do it when symptomatic or per your clinician’s advice; avoid smoking or caffeine beforehand.

Typically the last routine scan is the late‑pregnancy (third‑trimester) scan, usually around 36 weeks. It assesses fetal growth, amniotic fluid, placental position and the baby’s presentation to help plan labour. Not every pregnancy requires this scan; some have only earlier scans, and extra scans may be arranged later if concerns arise—your care provider will advise.

A positive Doppler means abnormal or reduced blood flow has been detected — commonly a blood clot (deep vein thrombosis), arterial narrowing/occlusion, or significant valve/placental flow problems. It usually prompts confirmatory imaging, specialist referral and prompt treatment (anticoagulation for DVT, revascularization or surgery for arterial blockages), monitoring for complications, and follow‑up to guide ongoing care. Timely treatment reduces risk of pulmonary embolism or tissue loss.