A baby's heart rate changes more in the first ten weeks than at any other time. It is first seen at around 6 weeks at roughly 117 beats per minute (bpm), climbs to a peak of about 176 bpm at 9 weeks, and then drifts slowly down to around 140 bpm in the third trimester. A rate is always read against the week it was measured.
This page has the published fetal heart rate range for each week from 6 to 10 and from 20 to 40, a checker for the number on your scan report, and what a slow or a fast rate does and does not mean. It also covers why the heart rate cannot tell you the sex and why a home Doppler is not a safe way to check on your baby.
The short answer: a normal fetal heart rate is about 103–128 bpm at 6 weeks, 158–186 bpm at 8 weeks and 162.4–188 bpm at 9 weeks, when it peaks. From 20 weeks it runs about 132–162 bpm, easing to about 119–155 bpm by 40 weeks. In labour, a stable baseline of 110–160 bpm is normal.
Fetal heart rate chart: 6 to 10 weeks
The largest open reference for the first weeks comes from Ouyang and colleagues, who measured the heart rate on transvaginal scans in 30,416 IVF pregnancies that all ended in a healthy live birth. IVF dates are exact, because the day of the embryo transfer is known, which makes this a clean picture of how fast the rate changes week by week.
| Weeks | Median, bpm | 5th–95th percentile, bpm | Pregnancies |
|---|---|---|---|
| 6+0 – 6+6 | 117 | 103 – 128 | 20,272 |
| 7+0 – 7+6 | 146 | 124 – 164.5 | 2,969 |
| 8+0 – 8+6 | 174 | 158 – 186 | 4,109 |
| 9+0 – 9+6 | 176 | 162.4 – 188 | 2,267 |
| 10+0 – 10+6 | 174 | 160 – 186 | 799 |
Source: Ouyang et al., BMC Pregnancy and Childbirth 2020, Table 3. Single-baby IVF pregnancies at one centre in China, dated from the embryo transfer, heart rate by M-mode. Ranges from other clinics and machines can differ by a few beats.
Why the heart rate rises and then falls
The heart starts beating before the nerves that will later slow it are working. In the first weeks the rate is set by the heart's own pacemaker cells, and it rises steeply as the heart grows: in Ouyang's data the median went from 117 bpm at 6 weeks to 174 bpm at 8 weeks. The peak comes at 9 weeks, at a median of 176 bpm. After that, the part of the nervous system that slows the heart matures and the rate eases down.
For 11 to 19 weeks we found no open, week-by-week range that we could check, so this page does not print one. One large study gives the direction: in 25,000 normal pregnancies, Liao and colleagues found the average fell from 170 bpm at a crown-rump length of 35 mm (about 10+2 weeks) to 155 bpm at 84 mm (about 14+2 weeks).
Fetal heart rate checker
Enter the week of the scan and the heart rate on your report. The checker places it against the published range for that week and says whether it is inside, below or above it. It never calls a result abnormal: one number from a scan cannot do that.
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Whatever the number: bleeding with pain early on, or a baby moving less than usual later on, needs a call the same day.
Fetal heart rate chart: 20 to 40 weeks
From the second half of pregnancy the heart rate falls slowly, by under one beat a week on average. The table below comes from a Norwegian study that scanned 294 low-risk pregnancies repeatedly from 20 weeks to term and published separate ranges for boys and girls. The mean and the middle 90% are shown for each.
| Week | Boys, mean | Boys, 5th–95th | Girls, mean | Girls, 5th–95th |
|---|---|---|---|---|
| Week 20 | 147 | 132 – 162 | 147 | 134 – 161 |
| Week 21 | 146 | 131 – 161 | 146 | 133 – 160 |
| Week 22 | 145 | 130 – 160 | 146 | 132 – 159 |
| Week 23 | 144 | 129 – 159 | 145 | 132 – 159 |
| Week 24 | 143 | 129 – 158 | 144 | 131 – 158 |
| Week 25 | 142 | 128 – 158 | 144 | 130 – 158 |
| Week 26 | 142 | 127 – 157 | 143 | 129 – 157 |
| Week 27 | 141 | 126 – 156 | 143 | 129 – 157 |
| Week 28 | 141 | 126 – 156 | 142 | 128 – 157 |
| Week 29 | 140 | 125 – 156 | 142 | 127 – 156 |
| Week 30 | 140 | 124 – 155 | 141 | 127 – 156 |
| Week 31 | 139 | 124 – 155 | 141 | 126 – 156 |
| Week 32 | 139 | 123 – 155 | 141 | 126 – 156 |
| Week 33 | 138 | 123 – 155 | 140 | 125 – 156 |
| Week 34 | 138 | 122 – 154 | 140 | 125 – 156 |
| Week 35 | 138 | 121 – 154 | 140 | 124 – 155 |
| Week 36 | 137 | 121 – 154 | 139 | 124 – 155 |
| Week 37 | 137 | 120 – 154 | 139 | 124 – 155 |
| Week 38 | 137 | 120 – 154 | 139 | 123 – 155 |
| Week 39 | 136 | 120 – 154 | 139 | 123 – 155 |
| Week 40 | 136 | 119 – 154 | 138 | 123 – 155 |
Source: Widnes et al., Biology of Sex Differences 2018, Tables 8 and 9. 294 low-risk single pregnancies in Tromsø, Norway, 1,261 scans; heart rate from umbilical artery Doppler.
A larger German study of almost 79,000 heart tracings found the same slow fall, about 0.4 bpm a week, and concluded that a normal baseline sits between 120 and 160 bpm. At term the average baseline was about 136 bpm.
What 110 to 160 bpm means in labour
In labour, the heart rate is watched continuously or listened to at intervals, and what matters is the baseline: the average rate over about ten minutes, between accelerations and dips. NICE and FIGO both treat a stable baseline of 110 to 160 bpm as normal. Babies born before their due date tend to sit towards the top of that range and babies born after it towards the bottom.
NICE grades anything from 100 to 109 bpm, or a rise of 20 bpm or more from the start of labour, as a reason for closer review, and a baseline below 100 or above 160 bpm as one that needs action. Those labels belong to a whole monitoring trace. They do not apply to a single reading taken during a scan.
A slow heart rate in early pregnancy
A slow rate in the first weeks is linked to a higher chance of miscarriage, but it is not a diagnosis. Doubilet and Benson put the lower limit of normal at 100 bpm up to 6.2 weeks and 120 bpm from 6.3 to 7.0 weeks. In their later study of embryos below those limits, 61.6% were still alive at the end of the first trimester, against 91.5% with a normal rate, and most of the survivors were born healthy.
ACOG advises against diagnosing a pregnancy loss from a slow heart rate alone and recommends another scan in 7 to 10 days. Dates matter here too: if you ovulated a few days later than your period suggests, a rate that looks slow for the week can be right for the real age of the pregnancy.
A fast early rate is rarely a concern on its own. In one study of embryos above the usual upper limit before 7 weeks, 37 of 41 were still doing well at the end of the first trimester.
When can you first see the heartbeat?
Usually from around 6 weeks on a transvaginal scan, once the embryo is a few millimetres long. Not seeing it before then is common and expected. NICE sets the rules for what happens if no heartbeat is seen, based on the size of the embryo and a repeat scan at least 7 days later; the early ultrasound guide explains them, and the CRL chart shows how big the embryo should be at each stage.
Can the heart rate tell you the baby's sex?
No. The folk rule says above 140 bpm means a girl, but a 2023 meta-analysis of first-trimester scans found no meaningful difference between boys and girls. In the Norwegian data above, girls' rates were slightly higher from 26 weeks, by 1 to 3 bpm: far too little to tell one baby from another, as the overlapping ranges in the table show. Our guide to when you can find out the sex covers the methods that do work.
Why not check the heartbeat at home?
Home Dopplers are sold to let you listen to your baby between appointments. The NHS advises against them, and the UK medicines regulator notes that the NHS and professional bodies do not recommend them for anyone who is not a midwife or doctor. In untrained hands a Doppler easily picks up your own pulse or the blood flow in the placenta. Australia's regulator has removed unsupervised home-use Dopplers from sale after reports of parents who were falsely reassured and delayed getting help.
Hearing a heartbeat does not show that a baby is well. From the second half of pregnancy, your baby's movements are the sign to watch, and a change in them needs a call to your maternity unit, not a Doppler.
When to call your doctor or midwife the same day
Call your maternity unit or early pregnancy unit straight away, even at night, if: your baby is moving less than usual or the pattern of movements has changed; you have vaginal bleeding, especially with pain; you have severe tummy pain, pain on one side or pain at the tip of your shoulder in early pregnancy; or you feel faint. Do not wait for a booked scan, and do not use a home Doppler to decide. Call 999 or 911, or your local emergency number, for heavy bleeding or if you collapse.
A heart rate figure on a report is never on this list by itself. A reading outside the range is something to talk through with whoever did the scan or at your next appointment.
Frequently Asked Questions
What is a normal fetal heart rate at 6 weeks?
In the largest open dataset, 20,272 pregnancies scanned at 6 weeks, the median was 117 bpm and the middle 90% ran from 103 to 128 bpm. The rate climbs fast this week, so a few days' difference in dates changes what is expected. A single early reading below the range is a reason for a repeat scan, not a diagnosis.
What is a normal fetal heart rate at 8 weeks?
At 8 weeks the median in Ouyang and colleagues' data was 174 bpm, with the middle 90% between 158 and 186 bpm. That is close to the fastest the heart will beat in the whole pregnancy: the rate peaks at about 176 bpm at 9 weeks and then slowly falls.
When is a baby's heart rate highest?
At about 9 weeks. The heart rate rises steeply from the first beats at around 6 weeks, reaches a median of 176 bpm at 9 weeks and then drifts down for the rest of the pregnancy, to around 136 to 138 bpm on average at 40 weeks. The fall reflects the nervous system maturing, not a problem.
What is a normal fetal heart rate at 20 weeks?
In a Norwegian study that followed 294 pregnancies, the average at 20 weeks was 147 bpm for boys and 147 bpm for girls, with the middle 90% between 132 and 162 bpm for boys and 134 and 161 bpm for girls. The two ranges overlap almost completely.
What is a normal fetal heart rate in the third trimester?
Usually between about 120 and 155 bpm. At 36 weeks the Norwegian study found averages of 137 bpm for boys and 139 bpm for girls, with the middle 90% from 121 to 155 bpm across both. In labour, NICE and FIGO treat a stable baseline of 110 to 160 bpm as normal.
Is a heart rate of 100 bpm at 6 weeks a bad sign?
Not on its own. Doubilet and Benson set the lower limit of normal at 100 bpm up to 6.2 weeks and 120 bpm at 6.3 to 7.0 weeks, and slow early rates are linked to a higher chance of miscarriage. Many such pregnancies continue normally, though, and ACOG advises against diagnosing a loss from a slow rate: it recommends another scan in 7 to 10 days.
Can I check my baby's heartbeat at home with a Doppler?
The NHS and the UK medicines regulator advise against it. A home Doppler can pick up your own pulse or the placenta and sound reassuring when the baby is not well, and hearing a heartbeat does not show that a baby is well. If movements slow down or change, call your maternity unit straight away instead of listening at home.
Fetal heart rate by week — at a glance
The fetal heart rate is first seen at around 6 weeks at a median of about 117 bpm, rises steeply to a peak of about 176 bpm at 9 weeks and then falls slowly for the rest of the pregnancy, to an average of about 136 to 138 bpm at 40 weeks. Published ranges are wide and specific to the week, so a figure is only meaningful against the week it was measured. A slow early rate calls for a repeat scan in 7 to 10 days rather than a diagnosis, and a fast one is rarely a concern on its own. In labour, a stable baseline of 110 to 160 bpm is normal. The heart rate cannot predict the baby's sex, and a home Doppler cannot show that a baby is well: changes in movement are the sign to act on.
Inside Baby Novum: the ultrasound tracker keeps each scan with its date, gestational week and a photo of the report, so the heart rate and measurements from one scan are there when you compare the next. One record is free; Premium keeps every scan with charts.
Read next
Sources
- Ouyang et al., BMC Pregnancy and Childbirth 2020 — Reference intervals of gestational sac, yolk sac, embryonic length and embryonic heart rate at 6–10 weeks after IVF
- Widnes et al., Biology of Sex Differences 2018 — Sex differences in umbilical artery Doppler indices: a longitudinal study
- Pildner von Steinburg et al., PeerJ 2013 — What is the "normal" fetal heart rate?
- Liao et al., Ultrasound in Obstetrics & Gynecology 2000 — Fetal heart rate in chromosomally abnormal fetuses
- Doubilet & Benson, Journal of Ultrasound in Medicine 1995 — Embryonic heart rate in the early first trimester: what rate is normal?
- Doubilet et al., Journal of Ultrasound in Medicine 1999 — Long-term prognosis of pregnancies complicated by slow embryonic heart rates
- Doubilet et al., American Journal of Roentgenology 2000 — Outcome of pregnancies with rapid embryonic heart rates
- ACOG Practice Bulletin 200 — Early Pregnancy Loss
- NICE NG229 — Fetal monitoring in labour: recommendations
- Ayres-de-Campos et al., FIGO consensus guidelines on intrapartum fetal monitoring: cardiotocography (2015)
- Nouri et al., BMC Pregnancy and Childbirth 2023 — The role of fetal heart rate in first trimester sonograms in prediction of fetal sex
- NHS — Your baby's movements
- MHRA — Medical devices: information for users and patients (fetal Dopplers)
- Therapeutic Goods Administration — Post-market review of home-use foetal Dopplers
Baby Novum is an informational and tracking tool, not a medical device, and does not provide medical diagnosis or treatment. Always consult your doctor or midwife about your pregnancy.