Pregnancy heart rate: what's normal, and when it isn't

Is my heart rate higher than normal during pregnancy?

Yes, and it is supposed to be. Resting heart rate rises by 10 to 20 beats per minute across pregnancy, on average, peaking late in the second and into the third trimester. (Sanghavi & Rutherford, Circulation, 2014) If your watch shows a number higher than your pre-pregnancy usual, that is what is supposed to happen. The numbers most pregnant women see are a normal cardiovascular adaptation, not a problem.

This article is the longer answer. What’s happening, what range is normal at your week, when it’s worth asking about, and what your Apple Watch is actually measuring.

Last reviewed: 5 May 2026.

Why does pregnancy raise resting heart rate?

Pregnancy increases blood volume by about 45 percent over the course of nine months. Cardiac output, the amount of blood your heart pumps per minute, rises 30 to 50 percent. To move that extra volume the heart speeds up, contracts more efficiently, and the resting rate climbs. (Sanghavi & Rutherford, Circulation, 2014)

The rise is not linear. Most of the climb happens in the first and early second trimester. Resting heart rate plateaus or peaks late in the second trimester, holds through most of the third, and drops back toward your pre-pregnancy baseline within a few weeks of birth.

What’s a normal resting heart rate by trimester?

A 2020 study in Obstetrics & Gynecology mapped vital-sign reference ranges across pregnancy. The averages and the upper limits for resting heart rate look like this. (Green et al, Obstetrics & Gynecology, 2020)

A few things follow from those numbers.

• A resting heart rate in the high 80s or low 90s in the third trimester is typical, not a red flag.
• If you were a resting-low-60s person before pregnancy, climbing to the high 70s by 12 weeks is the same biology as another woman climbing from 75 to the high 80s. The trajectory matters more than the number.
• Sustained tachycardia, defined clinically as a resting rate above 100 bpm, is at or above the 90th percentile for every stage. It is worth raising with your GP or midwife.

When is a high heart rate worth asking about?

Most elevated resting rates during pregnancy are normal. A few patterns are worth a phone call. ACOG groups them under tachycardia in pregnancy and is explicit about the red flags. (Tachycardia in pregnancy, PMC review)

• Resting heart rate above 110 bpm sustained over multiple readings. Particularly if it has appeared suddenly. A single spike is rarely meaningful; a multi-day shift is.
• Palpitations combined with chest pain, shortness of breath, or fainting. Any of those three companions turns palpitations from a sensation into a symptom. Call.
• Heart rate climbing alongside rising blood pressure or sudden swelling in the hands or face. That combination can point to preeclampsia, which has its own threshold of 140 over 90 mmHg, sustained over two readings four hours apart. (Practice Bulletin 222, ACOG, 2020)
• Persistent racing heart at rest, especially with thyroid symptoms (heat intolerance, weight loss, tremor). Pregnancy occasionally unmasks gestational hyperthyroidism, which is treatable but should be diagnosed.

None of these are reasons to panic. They are reasons to ask. A clinician can look at the trend in 10 minutes and tell you whether it’s the volume change or something else.

What is my Apple Watch actually measuring?

The watch measures heart rate optically. A green LED on the underside of the case lights up the capillaries on your wrist; a photodiode reads how much light is absorbed. Blood absorbs more light than surrounding tissue, so the pulse shows up as a periodic dip in reflected light. The watch counts those dips, smooths them across a few seconds, and reports a number.

Two things follow. First, the watch is reliably accurate for resting heart rate trends. The slow, week-on-week change pregnancy produces is well within what optical sensors can pick up. The Apple Watch’s resting heart rate value, the one that shows up overnight, is the most clinically useful number on the dial.

Second, the watch is less reliable for short bursts and for arrhythmia detection. If you feel a pattern of irregular beats and the number looks normal, the issue may be rhythm rather than rate. The watch’s ECG feature, available on Series 4 and later, captures rhythm and is the right tool for that conversation.

For pregnancy specifically, the resting heart rate trend is the read worth watching. Day to day it will fluctuate. Week to week, the climb is the picture.

What about my blood pressure?

Heart rate and blood pressure don’t move together. Pregnancy raises heart rate; it usually slightly lowers blood pressure through the second trimester before rising back to pre-pregnancy levels in the third. A high heart rate with normal blood pressure is a different conversation than a high heart rate with rising blood pressure.

ACOG’s threshold for gestational hypertension is 140 over 90 mmHg, sustained over two readings taken at least four hours apart. (Practice Bulletin 222, ACOG, 2020) If you have a home cuff that syncs to Apple Health, that is the number worth tracking against the threshold. A heart rate spike on its own is rarely the thing to panic about. A heart rate spike alongside a blood pressure reading at or above 140/90 is a phone call.

What myCocoon does with this number

myCocoon reads your resting heart rate from Apple Health, in private, and watches the trend rather than the single number. The app builds a rolling 14-day picture of your own usual. It surfaces a quiet card on the home view only if the trend has shifted in a way that is worth surfacing, and even then, only when it lines up with something else at the same time, like sleep slipping or evening step count well below your usual.

It does not chime. It does not push a notification for every elevated reading. The number stays on your device. It is not synced to iCloud, not stored on a myCocoon server, and never sent to a cloud language model as a raw value. Walking into your 28-week appointment with a fortnight of trend data, instead of a feeling, is what the app is for.

A longer write-up of how this works lives at How a pregnancy app reads what’s already on your phone, and the post on ambient intelligence covers what changes when an app does this kind of quiet reading on your behalf.

Common questions

Is a resting heart rate of 100 bpm normal during pregnancy? Sometimes, but it’s at the upper edge. Resting heart rate rises 10 to 20 bpm across pregnancy, peaking around 90 bpm on average at 34 weeks. Sustained rates above 100 bpm at rest, or sudden jumps without an obvious cause, are worth raising with your GP or midwife.

Why does my heart rate feel louder when I lie down? Blood volume rises by about 45 percent during pregnancy. The bigger volume plus a relaxed, flat-on-your-back position makes the pulse easier to feel and easier to hear. It is not usually a sign of anything wrong, but the sensation is real.

Does caffeine raise pregnancy heart rate? Yes, the same way it does outside pregnancy, and the effect can feel more pronounced because resting rate is already higher. ACOG considers up to 200 mg of caffeine per day, about one 12 oz cup of coffee, compatible with pregnancy.

When should I call my GP about my heart rate? Call if your resting heart rate stays above 110 bpm, if you have palpitations with chest pain or breathlessness, if you feel faint, or if your heart rate spikes alongside high blood pressure or sudden swelling. Those are red flags ACOG names.

Is my Apple Watch heart rate accurate enough during pregnancy? Yes, for resting heart rate trends. Optical wrist sensors are reliable for the kind of slow week-on-week change pregnancy produces. They are less reliable for arrhythmia detection, which is what an ECG is for.

Bottom line

Your heart rate during pregnancy will rise, on average 10 to 20 beats per minute, peaking late in the second trimester and holding through the third. Most of what your watch is showing you is the body adapting. The numbers worth asking about are the sustained ones above 110 bpm, the palpitations that come with other symptoms, and the heart rate that climbs alongside rising blood pressure. Otherwise, the climb is the climb. The right tool is a 14-day trend against your own usual, not a one-shot reading.

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