Heartbeat on ultrasound: when it shows and what to do if it does not yet
In short: on a transvaginal scan the embryo’s heartbeat usually shows from 5+5 to 6+2 weeks, and from 6+3 to 7+0 weeks in practically every developing pregnancy. If it is not there at 6 weeks, the most common reason is that the pregnancy is younger than the calendar suggests, and the scan should be repeated in 7 to 14 days. Here is what the timing depends on, which heart rate is normal, and when an absent heartbeat is considered final.
Which week the heartbeat shows
Weeks of pregnancy are counted from the first day of the last period, not from conception. On the screen the heartbeat looks like a rapid flicker inside the embryo — at that point the embryo itself is only 2–5 mm long. The full picture — when the gestational sac, the yolk sac and the embryo appear — is in my article on when pregnancy shows on ultrasound.
| Weeks | Transvaginal scan | Abdominal scan |
|---|---|---|
| 5+0 – 5+4 | gestational sac and yolk sac; the embryo is usually not visible yet | often nothing visible |
| 5+5 – 6+2 | embryo 2–5 mm, in most cases already with a heartbeat | gestational sac; heartbeat not always seen |
| 6+3 – 7+0 | heartbeat seen practically always | heartbeat seen in most cases |
| after 7 weeks | heartbeat always seen, embryo over 10 mm | heartbeat seen |
Through the abdomen everything shows about a week later: the probe is further from the uterus and fine detail is lost. That is why I scan transvaginally in early pregnancy — it is safe for the pregnancy.
Why the heartbeat may not be visible at 6 weeks
- The pregnancy is younger than calculated. This is the most common reason. If ovulation was later than day 14 or the cycle is longer than 28 days, the pregnancy is a few days “younger” than the calendar, and at this stage each day changes the picture.
- The scan was done through the abdomen. With that approach the heartbeat shows about a week later.
- The position of the uterus or a fibroid gets in the way. The image is poorer and a tiny embryo is hard to display fully.
- The pregnancy has stopped developing. This happens, but from a single early scan that conclusion is drawn only under strict conditions — listed below.
When an absent heartbeat is considered final
The criteria are deliberately strict — to rule out an error in a wanted pregnancy:
- the embryo (crown–rump length) is 7 mm or more and has no heartbeat;
- the mean gestational sac diameter is 25 mm or more and there is no embryo;
- two weeks after a scan that showed a gestational sac without a yolk sac, there is still no embryo with a heartbeat;
- 11 days after a scan that showed a gestational sac with a yolk sac, there is still no embryo with a heartbeat.
Anything short of these limits is a “suspicion”, not a diagnosis, and needs a repeat scan. A diagnosis of a non-viable pregnancy is usually confirmed by a second doctor or a second scan.
Which heart rate is normal
In the first days the embryo’s heart beats relatively slowly, then the rate rises quickly, peaks around 9 weeks and then drops slightly.
| Weeks | Heart rate, beats per minute |
|---|---|
| up to 6+2 | 100–120 |
| 6+3 – 7+0 | 120–150 |
| 8–10 | 140–180 |
| 12–13 | 140–170 |
The lower limit matters more than the upper: up to 6+2 weeks, 100 beats per minute or more is considered normal; from 6+3 to 7+0 weeks, 120 or more. A slower rate is not a diagnosis but a reason to repeat the scan in 7 to 10 days: the rate often evens out in that time, especially when the pregnancy is in fact younger.
The heart rate cannot tell you the baby’s sex — that is a myth: there is no difference between boys and girls in the first trimester.
Seen or heard
On an early scan the heartbeat is seen, not heard. I measure the rate from the movement on the screen, in what is called M-mode. The “sound of the heart” comes from pulsed Doppler; in the first trimester it is not switched on without a reason — as recommended by ISUOG, the international society of ultrasound in obstetrics. This does not affect the accuracy of the scan.
What it means for the pregnancy
When the scan shows a gestational sac in the uterus, an embryo and a heartbeat, three things can be said: the pregnancy is inside the uterus, it is developing, and its age has been set from the size of the embryo more precisely than from the calendar. From that point the risk of losing the pregnancy is clearly lower than before. What follows is routine care; how it is organised in Poland is in my article on the first ultrasound and the schedule of scans.
When not to wait for the repeat scan
- severe pain in the lower abdomen, especially on one side, or shoulder pain;
- heavy bleeding — a pad soaked within an hour;
- weakness, dizziness, fainting.
With these symptoms you need help the same day: call 112 or go to a hospital emergency department. Light spotting in early pregnancy is common and not always dangerous, but it is worth telling your doctor about it without waiting for the scheduled date.
How it works at my practice
At an early pregnancy scan I check where the gestational sac is, measure the embryo, count the heart rate and set the dates. If the calendar says less than six weeks, I will tell you up front that the heartbeat may not be visible yet — so that an empty screen does not become a reason to panic. You get the report straight away.
- pregnancy ultrasound up to 10 weeks — 250 zł;
- consultation in pregnancy — 300 zł.
I see patients in Warsaw, in the Targówek district, at ul. Głębocka 9/U1. Appointments are not held in English — bring someone who can interpret, or tell me in advance. No referral or insurance is needed. To book, leave a request on the booking page, call or message me.
Short answers
Which week does the heartbeat show on ultrasound?
On a transvaginal scan — usually from 5+5 to 6+2 weeks, when the embryo is 2–5 mm long. From 6+3 to 7+0 weeks the heartbeat shows in practically every developing pregnancy. Through the abdomen it shows about a week later.
Six weeks and no heartbeat — is the pregnancy non-viable?
Not necessarily. Most often the pregnancy is younger than the calendar suggests. If the embryo is smaller than 7 mm, no diagnosis is made and the scan is repeated no sooner than 7 days later.
What heart rate is normal at 6–7 weeks?
Up to 6+2 weeks — 100 beats per minute or more; from 6+3 to 7+0 weeks — 120 or more. Around 9 weeks the rate reaches 140–180 beats per minute.
When is an absent heartbeat considered final?
When the embryo is 7 mm or more with no heartbeat, or when a gestational sac with a mean diameter of 25 mm or more contains no embryo. With smaller measurements a repeat scan is needed.
Can the heart rate tell the baby’s sex?
No. In the first trimester the heart rate of boys and girls does not differ.
Is an early ultrasound harmful?
A standard ultrasound in the first trimester is considered safe. Pulsed Doppler, which gives the “sound of the heart”, is not used early in pregnancy without a reason.
Sources
The primary sources this text rests on. Links open in a new tab.
- Doubilet PM et al. Diagnostic Criteria for Nonviable Pregnancy Early in the First Trimester. N Engl J Med 2013;369:1443–1451the criteria for when an absent heartbeat is definitive and when it is a reason to repeat the scan
- NICE guideline NG126: Ectopic pregnancy and miscarriage: diagnosis and initial managementNICE, UK — when and after how many days the scan is repeated if no heartbeat is seen yet
- Doubilet PM, Benson CB. Embryonic heart rate in the early first trimester: what rate is normal? J Ultrasound Med 1995;14:431–434which embryonic heart rate is considered normal before 7 weeks
- ISUOG Practice Guidelines (updated): performance of 11–14-week ultrasound scan. Ultrasound Obstet Gynecol 2023;61:127–143the ISUOG guidelines — ultrasound safety in the first trimester and why Doppler is not used early without a reason
This text describes the general picture and does not replace a consultation. Timings and indications differ from woman to woman and are decided at the appointment, from your history and test results.
