Fetal Heart Rate: Normal Range by Week and What It Means for Your Baby
Fetal heart rate normal range by pregnancy week explained by an OB/GYN — what 120–160 bpm means, why the rate changes by trimester, what variability indicates, and when to be concerned.
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Table of Contents
- What Is the Fetal Heart Rate?
- Normal Fetal Heart Rate by Week of Pregnancy
- Understanding Fetal Heart Rate Variability
- Accelerations: The Most Reassuring Pattern
- Decelerations: When the Heart Rate Drops
- Methods of Monitoring Fetal Heart Rate
- The Old Myth: Heart Rate and Baby's Sex
- When to Call Your Midwife or Doctor
- Frequently Asked Questions (FAQ)
- References and Further Reading
What Is the Fetal Heart Rate?
The fetal heart rate (FHR) is the number of times the fetal heart beats per minute (bpm). It is controlled by the fetal autonomic nervous system — the same system that regulates adult heart rate through the balance of the sympathetic (accelerating) and parasympathetic (slowing) nervous branches.
Unlike adult hearts, which beat at 60–100 bpm at rest, the fetal heart beats significantly faster because:
- The fetal heart is small and must beat rapidly to circulate blood effectively through the developing body
- Fetal metabolism is highly active, driving high oxygen demand
- The parasympathetic nervous system (which slows heart rate) matures gradually through pregnancy, so early in gestation the sympathetic system predominates
The fetal heart begins beating remarkably early — as early as 22 days after conception (approximately 5 weeks gestational age). It is detectable on transvaginal ultrasound from around 6 weeks and by Doppler from approximately 10–12 weeks.
Normal Fetal Heart Rate by Week of Pregnancy
The fetal heart rate is not static across pregnancy — it follows a characteristic arc that reflects the maturation of the fetal nervous system.
First Trimester (Weeks 6–13)
| Gestational Age | Normal FHR Range |
|---|---|
| 6 weeks | 100–115 bpm |
| 7 weeks | 125–135 bpm |
| 8 weeks | 145–165 bpm |
| 9 weeks | 165–175 bpm (peak) |
| 10 weeks | 160–170 bpm |
| 11–13 weeks | 150–165 bpm |
Key pattern: The fetal heart rate rises rapidly in the first few weeks as the cardiac conduction system develops, peaks at approximately 9–10 weeks (often reaching 170–180 bpm), and then begins a gradual decline as the parasympathetic nervous system matures and gains influence.
"A heart rate at 9 weeks that seems alarmingly fast to parents — 170 bpm — is actually exactly what we expect to see," says Dr. Preeti Agarwal. "The concern in early pregnancy is a heart rate that is too slow, or one that is not increasing appropriately week by week on serial scans."
A first-trimester heart rate below 100 bpm is associated with an increased risk of miscarriage and warrants close monitoring. A rate below 80 bpm is strongly predictive of pregnancy loss.
Second Trimester (Weeks 14–27)
| Gestational Age | Normal FHR Range |
|---|---|
| 14–20 weeks | 140–160 bpm |
| 20–27 weeks | 130–155 bpm |
By the second trimester, the fetal heart rate has settled into the classic range most people recognise. The parasympathetic nervous system is now contributing meaningfully to heart rate regulation, bringing the average down from the first-trimester peaks.
Variability — small, beat-to-beat fluctuations in the heart rate — begins to become apparent in the second trimester as the autonomic nervous system matures. This variability is a reassuring sign; it indicates that the fetal nervous system is responsive and developing appropriately.
Third Trimester (Weeks 28–40)
| Gestational Age | Normal FHR Range |
|---|---|
| 28–40 weeks | 110–160 bpm |
The normal range in the third trimester is the one most people are familiar with: 110–160 beats per minute. This is the range used in cardiotocography (CTG) monitoring — the standard fetal wellbeing assessment in late pregnancy and labour.
Within this range, you will notice natural fluctuations:
- Heart rate accelerates with fetal movement (these accelerations are reassuring)
- Heart rate may slow briefly with uterine contractions or fetal sleep cycles (interpretation depends on the pattern)
- Baseline heart rate is typically highest in the morning and lowest in the evening for most fetuses
Understanding Fetal Heart Rate Variability
Variability refers to the fluctuation in the baseline heart rate from one beat to the next — the degree to which the heart rate goes up and down continuously rather than staying at a perfectly flat line.
Normal variability is 6–25 bpm of fluctuation around the baseline. It indicates that the fetal autonomic nervous system is active, the fetus is neither compromised nor profoundly sleeping, and the brain-heart axis is functioning well.
Categories of Variability (CTG Interpretation)
| Variability | Range | Interpretation |
|---|---|---|
| Absent | Undetectable | Concerning — may indicate severe fetal compromise or deep sleep |
| Minimal | < 5 bpm | Concerning if persistent — may indicate fetal compromise, sedation, or prematurity |
| Normal | 6–25 bpm | Reassuring — indicates healthy autonomic function |
| Marked (saltatory) | > 25 bpm | May be associated with acute hypoxia or umbilical cord compression |
Important: Reduced variability during a period of fetal sleep (typically lasting 20–40 minutes) is completely normal. If a CTG trace shows minimal variability, the midwife may use vibroacoustic stimulation (a buzzer applied to the abdomen) to wake the baby and reassess.
Accelerations: The Most Reassuring Pattern
An acceleration is a transient rise in fetal heart rate of at least 15 bpm above baseline, lasting at least 15 seconds (in fetuses ≥32 weeks). In earlier gestation, the threshold is 10 bpm for 10 seconds.
Accelerations occur in response to:
- Fetal movement
- Uterine contractions (a reassuring response)
- Tactile or acoustic stimulation
Two or more accelerations in a 20-minute period is the definition of a reactive, reassuring CTG trace. Accelerations are the single most reliable indicator of fetal wellbeing on a CTG.
Their presence means: the fetal nervous system is responsive, oxygenation is adequate, and the fetus is not compromised at the time of monitoring.
Decelerations: When the Heart Rate Drops
A deceleration is a transient fall in fetal heart rate of at least 15 bpm below baseline, lasting at least 15 seconds. Not all decelerations are equally concerning — their timing relative to contractions is what determines clinical significance.
Early Decelerations
- Mirror the shape of the contraction exactly
- Begin and end with the contraction
- Caused by vagal response to fetal head compression during contractions
- Normal and benign — commonly seen in active labour
Variable Decelerations
- Variable in shape, timing, and duration
- Often abrupt onset and recovery
- Caused by umbilical cord compression
- Common in labour; assessed by severity, depth, and recovery pattern
- Mild variable decelerations are often acceptable; severe, prolonged variable decelerations require close attention
Late Decelerations
- Begin after the peak of the contraction and recover after the contraction ends
- The hallmark pattern of uteroplacental insufficiency — inadequate oxygen delivery through the placenta
- Always pathological and require immediate assessment
- Even shallow late decelerations (just 10–15 bpm below baseline) are clinically significant
Prolonged Decelerations
- A fall in FHR lasting more than 2 minutes
- Requires immediate midwifery or medical assessment
- A prolonged deceleration lasting more than 3 minutes is a fetal emergency — immediate intervention is required
Methods of Monitoring Fetal Heart Rate
Doppler Ultrasound (Handheld)
Used from approximately 10–12 weeks onward. A handheld device uses ultrasound waves to detect the fetal heartbeat and produce a characteristic whooshing sound. Commonly used at antenatal appointments from the second trimester. Provides a heart rate number but no information about variability or the response to contractions.
Cardiotocography (CTG / EFM)
The gold standard for fetal monitoring in late pregnancy and labour. A transducer placed on the mother's abdomen records both the fetal heart rate and uterine contractions simultaneously, producing a paper or digital trace.
CTG is used:
- In the third trimester when fetal movements have reduced
- During induction of labour
- Continuously in high-risk labours
- When any concern arises during labour
A trained midwife or obstetrician interprets the CTG by assessing baseline rate, variability, accelerations, and decelerations together — no single feature is interpreted in isolation.
Fetal Echocardiography
A specialist ultrasound of the fetal heart structure and function, performed between 18–24 weeks. Recommended when:
- A cardiac abnormality is suspected on the anomaly scan
- Family history of congenital heart disease
- Maternal conditions associated with fetal cardiac risk (diabetes, lupus, anti-Ro antibodies)
- Fetal heart rate arrhythmia is detected
Intermittent Auscultation (IA)
In low-risk labours in midwifery-led settings, the fetal heart rate is monitored intermittently using a Pinard stethoscope or Doppler every 15 minutes in active labour, every 5 minutes in the second stage. This is evidence-based practice for uncomplicated labours and avoids the higher rate of instrumental delivery associated with continuous CTG in low-risk women.
The Old Myth: Heart Rate and Baby's Sex
A persistent folk belief holds that a fetal heart rate above 140 bpm indicates a girl, and below 140 bpm indicates a boy. This has been studied multiple times and is conclusively false. There is no significant difference in fetal heart rate between male and female fetuses across any stage of pregnancy. The heart rate varies with gestational age, fetal activity, and maternal position — not with fetal sex.
When to Call Your Midwife or Doctor
Contact your midwife or maternity unit the same day if:
- Fetal movements have decreased — this is the most important and sensitive indicator of fetal wellbeing, and any perceived reduction warrants assessment
- You are 32 weeks or beyond and your baby's movement pattern has changed
- A Doppler reading at an appointment showed a rate outside the 110–160 bpm range in the third trimester
- You have a high-risk pregnancy (gestational diabetes, hypertension, growth restriction) and have any concern
Go in immediately (do not wait) if:
- You have not felt your baby move in several hours in the third trimester
- You feel fewer than 10 movements in 2 hours (using the count-to-ten method, if used by your unit)
- You were told a heart rate finding was concerning at a previous scan or appointment
Never hesitate to be assessed. There is no such thing as calling your midwife too many times about reduced fetal movement. The priority is always ruling out fetal compromise, not avoiding inconvenience.
Frequently Asked Questions (FAQ)
Q: What is a normal fetal heart rate at 8 weeks? A: At 8 weeks, a normal fetal heart rate is approximately 145–165 bpm. The fetal heart rate peaks at around 9–10 weeks (reaching up to 170–180 bpm in some healthy pregnancies) before gradually declining as the parasympathetic nervous system matures. A reading in the 150–175 range at 8–10 weeks is completely expected.
Q: Is 170 bpm too fast for a baby in the womb? A: It depends on gestational age. At 9–10 weeks, 170 bpm is within the normal range and is expected as the peak of first-trimester heart rate development. In the third trimester, a sustained baseline of 170 bpm would be considered tachycardia (above the 160 bpm upper limit) and would require investigation. Context — specifically gestational age — is everything when interpreting a fetal heart rate number.
Q: What does it mean if the baby's heart rate is 120 bpm? A: A heart rate of 120 bpm is at the lower boundary of the normal third-trimester range (110–160 bpm). On its own, 120 bpm is normal. If it is accompanied by absent variability, late decelerations, or reduced fetal movement, the overall CTG picture requires careful evaluation. Isolated rate of 120 with good variability and normal movements is reassuring.
Q: Can fetal heart rate predict baby's gender? A: No. Multiple studies have conclusively demonstrated that fetal heart rate does not reliably predict the sex of the baby. Both male and female fetuses have equivalent heart rates throughout pregnancy. The belief that girls have faster heartbeats is a myth with no scientific basis.
Q: What is fetal tachycardia and what causes it? A: Fetal tachycardia is a sustained baseline heart rate above 160 bpm in the third trimester, lasting more than 10 minutes. Causes include maternal fever (the most common cause — fetal heart rate rises approximately 10 bpm for each degree of maternal fever), maternal anxiety or exercise, fetal infection, fetal anaemia, fetal thyrotoxicosis (rare), and cardiac arrhythmias. Isolated, brief episodes of elevated rate during active fetal movement are not tachycardia.
Q: What is fetal bradycardia and should I be worried? A: Fetal bradycardia is a sustained baseline heart rate below 110 bpm in the third trimester. Brief, transient drops (variable decelerations) are common and often benign in labour. A sustained low baseline below 100 bpm, or a prolonged deceleration lasting more than 3 minutes, is an obstetric emergency requiring immediate assessment. In early pregnancy, a rate below 100 bpm at 6–8 weeks is associated with significantly increased miscarriage risk.
Q: How often is the fetal heart rate checked in pregnancy? A: In routine antenatal care, the fetal heart rate is checked at every appointment from approximately 12 weeks onward using a handheld Doppler. In high-risk pregnancies (gestational diabetes, hypertension, growth restriction, reduced movement), additional monitoring with CTG and Doppler ultrasound is performed more frequently. All women in established labour have their baby's heart rate monitored — continuously via CTG in high-risk labours, or intermittently in low-risk labours.
Q: My CTG showed reduced variability. Should I be worried? A: Reduced variability on a CTG has several possible causes, most of which are benign. The most common is a fetal sleep cycle — healthy fetuses have 20–40 minute quiet sleep periods during which variability temporarily decreases. Other causes include medications (such as morphine or certain antihistamines taken by the mother), prematurity, and in a smaller number of cases, fetal compromise. Your midwife or obstetrician will assess the whole trace — including the baseline rate, presence of accelerations, and presence of decelerations — and may use stimulation to rouse the baby before drawing any conclusions.
Q: What does it mean if no heartbeat is found on a Doppler? A: Before 10–12 weeks, a Doppler may not detect the heartbeat — this is normal and does not indicate a problem. The heart is simply too small and deep for the standard Doppler signal to reach reliably before this point. After 12 weeks, if a heartbeat is not found on Doppler, an ultrasound scan will confirm fetal viability. Failure to detect a heartbeat on Doppler is sometimes due to operator skill, maternal body habitus, fetal position, or equipment — it should trigger an ultrasound, not immediate alarm.
References and Further Reading
-
NICE Guideline CG190 — Intrapartum Care for Healthy Women and Babies:
https://www.nice.org.uk/guidance/ng235 -
ACOG — Intrapartum Fetal Heart Rate Monitoring:
https://www.acog.org/womens-health/faqs/fetal-heart-rate-monitoring-during-labor -
NHS — Monitoring Your Baby's Movement:
https://www.nhs.uk/pregnancy/keeping-well/your-babys-movements/ -
WHO — Managing Complications in Pregnancy and Childbirth:
https://www.who.int/publications/i/item/9789241565493 -
Ebbing C et al. — Reference Ranges for Fetal Heart Rate (Acta Obstetricia et Gynecologica Scandinavica):
https://pubmed.ncbi.nlm.nih.gov/17763169/ -
RCOG — Reduced Fetal Movements (Green-top Guideline No. 57):
https://www.rcog.org.uk/guidance/browse-all-guidance/green-top-guidelines/reduced-fetal-movements-green-top-guideline-no-57
Medical Disclaimer
This article is for informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Fetal heart rate interpretation is a clinical skill that requires evaluation of multiple parameters simultaneously, in the context of gestational age and the overall clinical picture. If you have any concerns about your baby's heart rate, movements, or wellbeing, contact your midwife or maternity unit immediately. Never delay seeking care based on information read online.
About the Author
Abhilasha Mishra is a health and wellness writer specializing in pregnancy monitoring, maternal-fetal medicine, and evidence-based obstetric care. She writes to help expectant parents understand the clinical information they encounter throughout pregnancy with accuracy and clarity.