GUIDE
The dating ultrasound (usually between weeks 6 and 9) confirms your pregnancy, measures the embryo, establishes your due date, and detects a heartbeat.
This is typically your first glimpse of your baby. The ultrasound uses sound waves to create an image — it is safe, painless, and takes about 15 to 20 minutes. It is one of the most emotionally significant moments of early pregnancy.
Be prepared from day one
The dating ultrasound — also called a viability scan or first-trimester ultrasound — is typically performed between weeks 6 and 9 of pregnancy, often at or near your first prenatal visit. Its primary purpose is medical: to confirm the pregnancy is developing in the uterus, establish an accurate due date, and detect a heartbeat.
ACOG recommends a first-trimester ultrasound for all pregnancies to establish the most accurate gestational dating. Due dates based on ultrasound measurement before 9 weeks are accurate to within plus or minus 5 days — more precise than dates based on your last menstrual period alone.
This ultrasound is usually transvaginal in early pregnancy because the embryo is small and positioned deep in the pelvis. The probe provides much clearer images than an abdominal scan at this stage.
| Gestational Age | What Is Visible |
|---|---|
| 5–6 weeks | Gestational sac and possibly a yolk sac. The embryo may not yet be visible. |
| 6–7 weeks | Embryo with a fetal pole (tiny shape). Heartbeat may be detected as a flicker. |
| 7–8 weeks | Embryo with visible heartbeat. Crown-rump length measured to establish due date. |
| 8–9 weeks | Embryo with limb buds visible. Head and body becoming more distinct. Clear heartbeat. |
| 9–10 weeks | Embryo starting to look more human. Movement may be visible. Size approximately 1 inch. |
This scan gives your provider the baseline information needed to plan the rest of your prenatal care.
The sonographer measures the crown-rump length (CRL) — the distance from the top of the embryo's head to its bottom. This measurement is entered into a standard formula that calculates gestational age with high accuracy.
If the ultrasound-based gestational age differs from your LMP-based estimate by more than 5 to 7 days, your due date will be updated. The ultrasound date becomes your official estimated due date (EDD) because first-trimester CRL measurements are the gold standard for pregnancy dating.
An accurate due date matters because it determines the timing of every subsequent screening and test in your prenatal visit schedule — from the NIPT window to the anatomy scan to decisions about induction at term.
Some providers perform a dating ultrasound for all patients. Others only do so if there is a specific clinical reason.
Not detecting a heartbeat at a very early scan (5-6 weeks) does not necessarily mean something is wrong. The heartbeat begins around day 22 after conception, but on ultrasound it may not be reliably visible until 6 to 7 weeks. If you are earlier than expected — which is common when cycles are irregular — the heartbeat simply may not have started yet.
Your provider will typically schedule a follow-up scan in 7 to 14 days if no heartbeat is seen before 7 weeks. They will look for growth of the gestational sac and embryo, and for the emergence of a heartbeat. ACOG guidelines specify that a definitive diagnosis of pregnancy loss should not be made from a single early scan.
If a heartbeat is detected, the risk of miscarriage drops significantly — to about 5 percent or less once a normal heartbeat is seen on ultrasound at 7 to 8 weeks.
Scheduling your dating ultrasound too early (before 6 weeks) often means being called back for a repeat because there is not enough to see yet. If your provider gives you a choice, 7-8 weeks is often the sweet spot — late enough to see a clear heartbeat, early enough to establish an accurate due date.
For a transvaginal ultrasound, you will undress from the waist down and lie on the exam table with your feet in stirrups. The sonographer will cover a slim probe with a disposable cover and lubricant before gently inserting it. The procedure is not painful, though some people feel mild pressure.
The scan takes about 15 to 20 minutes. The sonographer will take measurements and capture images. Some providers will show you the screen and point out what they see; others will have you meet with your provider afterward to review the images.
Many people find this ultrasound deeply emotional — it is often the first tangible proof of the pregnancy. Whether you feel excitement, relief, anxiety, or a mix of everything, your reaction is completely normal.
For a complete picture of what comes next, see our nuchal translucency scan guide (weeks 11-14), our pregnancy blood tests guide, and the prenatal vitamins guide to make sure your nutrition is on track.
This guide is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider with any questions about your pregnancy.
