What it is (overview)

A Pregnancy Umbilical Artery Doppler Ultrasound Scan (Doppler USS) is a non-invasive prenatal imaging test that uses ultrasound and Doppler technology to assess blood flow in the umbilical artery (one of the vessels in the umbilical cord). The umbilical artery carries blood from the baby to the placenta, so the flow pattern gives important information about how well the placenta is working and how effectively oxygen and nutrients are reaching the baby.

During the scan, a sonographer places gel on your abdomen and moves an ultrasound probe over the skin, similar to a routine pregnancy scan. Doppler ultrasound measures the speed and pattern of blood flow and generates waveforms and indices (commonly reported as S/D ratio, Resistance Index (RI), and Pulsatility Index (PI)). These values reflect how much resistance the blood meets as it travels through the placenta.

In plain language, the results are interpreted like this:

• Normal/low resistance flow: Usually suggests the placenta is allowing good blood flow and the baby is likely receiving adequate oxygen and nutrients.
• Increased resistance (higher PI/RI or S/D ratio): Can suggest reduced placental function (sometimes called placental insufficiency) and may be associated with fetal growth restriction or a baby that is not growing as expected.
• Absent end-diastolic flow or reversed end-diastolic flow: More concerning patterns that can indicate significant placental resistance and a higher risk of fetal compromise; these findings typically lead to closer monitoring and sometimes earlier delivery depending on gestational age and other test results.

This is a painless test and does not involve radiation. It is commonly used in obstetrics as part of prenatal monitoring in the second trimester and especially the third trimester, often alongside growth scans, amniotic fluid assessment, and fetal wellbeing checks.

When & why it's usually done

An umbilical artery Doppler ultrasound is usually ordered when your clinician wants a clearer picture of fetal health and placental blood flow, particularly if there is concern that the baby may not be getting enough oxygen or nutrition through the placenta.

Common reasons it may be recommended include:

• Suspected fetal growth problems: If the baby measures small for dates, there is concern for fetal growth restriction (FGR/IUGR), or fundal height/growth scan suggests slowed growth.
• Reduced fetal movements: If you report a noticeable decrease in baby's movements, Doppler USS may be part of a broader assessment (often with CTG or biophysical profile).
• High blood pressure disorders in pregnancy: Including gestational hypertension or preeclampsia, where placental function may be affected.
• Maternal medical conditions: Such as diabetes, kidney disease, autoimmune disease (e.g., lupus/antiphospholipid syndrome), or significant anemia, which can increase the risk of placental complications.
• Previous pregnancy complications: Prior fetal growth restriction, stillbirth, placental insufficiency, or early-onset preeclampsia may prompt closer Doppler monitoring in a new pregnancy.
• Multiple pregnancy or abnormal placentation concerns: In some twin pregnancies or when placental issues are suspected, Doppler may assist with risk assessment (your care team will tailor the approach to your pregnancy type).

The test is also used to guide decisions about how often monitoring is needed and, in some cases, timing of delivery. Results are interpreted together with gestational age, baby's growth pattern, amniotic fluid levels, and other fetal wellbeing tests rather than in isolation.

Common diseases related to it

• Fetal growth restriction (FGR) / intrauterine growth restriction (IUGR)
• Placental insufficiency (uteroplacental insufficiency)
• Preeclampsia
• Gestational hypertension
• Chronic hypertension in pregnancy
• Oligohydramnios (low amniotic fluid), when linked with placental problems
• Fetal hypoxia / fetal compromise (suspected reduced oxygen delivery)
• Diabetes in pregnancy (pre-existing diabetes or gestational diabetes) with suspected placental or growth concerns
• Autoimmune or clotting-related pregnancy complications (e.g., antiphospholipid syndrome) affecting placental blood flow

Health goals where it may help

• Monitoring overall fetal wellbeing by assessing umbilical artery blood flow
• Evaluating placental health and identifying early signs of placental insufficiency
• Supporting safer prenatal monitoring in the second and third trimester for higher-risk pregnancies
• Guiding follow-up frequency (e.g., growth scans and Doppler surveillance) when fetal growth restriction is suspected
• Helping clinicians plan the timing of delivery when blood flow patterns suggest increased risk to the baby
• Providing reassurance when fetal growth or movements raise concern but Doppler blood flow is normal