From restless sleep to a faster heart rate: How pregnancy changes your body and what expecting mothers should knowPublished on: Oct 6, 2026, 13:07:38 IST

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The body changes in surprising ways during pregnancy. Here’s what happens to sleep, heart rate, and body temperature.

Pregnancy is one of the most significant physiological transformations the human body undergoes, so it makes sense that biometrics and behaviours can look different than usual. Hormonal shifts, increased blood volume, cardiac output, and metabolism can all influence sleep, resting heart rate (RHR), heart rate variability (HRV), body temperature, and respiratory rate. These changes can be subtle, but they can significantly impact how a person feels throughout pregnancy. In an interview with Lifestyle, Dr Chris Curry, OB/GYN, physician and clinical director of Women’s Health at Oura, shared pregnancy changes every woman should be aware of.

First trimester

According to Dr Curry, sleep can be quite different in the first trimester. Research showed that participants spent more time in bed (more than 30 minutes more per night), but only about 15 of those minutes in bed resulted in additional sleep. “There are a few things known about early pregnancy that may contribute to this, like nausea and frequent trips to the bathroom making it harder to stay asleep at night,” highlighted Dr Curry.

There are also major changes happening in the body to adapt to the new pregnancy; body temperature and respiratory rate both begin to rise within the first few weeks, while RHR and HRV start shifting from their pre-pregnancy baselines.

Second trimester

Dr Curry highlighted that in this phase, the time in bed decreases in the second trimester compared to the first, and stays fairly stable throughout. Major changes continue to happen to the mother’s cardiovascular system (e.g., heart, blood vessels), which is represented in the data by a steady increase in RHR and a matching steady decrease in HRV.

Third trimester

“The actual time in bed in the third trimester was similar to prepregnancy; more of that time was spent awake, leading to overall less time spent asleep,” said Dr Curry. This trend continues right up until around birth, when time in bed starts to peak, while time asleep is at its lowest point of the pregnancy. There are many possibilities for why the analysis may have shown these changes in sleep, such as physical discomfort, frequent urination, difficulty getting comfortable, and anticipation around childbirth.

Postpartum

During postpartum, overall time in bed being is significantly lower than pre-pregnancy, and time awake but in bed time similarly being much higher. It will seem obvious to those who have cared for a newborn; the infant’s rhythms of feeding and sleeping often significantly impact the biometrics and sleep of the mother. “Changes in measures like RHR and HRV rapidly shift after delivery, with a notable return towards prepregnancy for all within days of delivery,” concluded Dr Curry.

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.

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