How pregnancy affects deep sleep

Key Points

Research suggests pregnancy can reduce deep sleep, especially in the third trimester, due to physical discomfort and hormonal changes.
It seems likely that pregnant women experience about 13 fewer minutes of deep sleep per night in the third trimester compared to the first.
The evidence leans toward individual variations, with some women maintaining better sleep quality, and no guaranteed way to fully restore deep sleep to pre-pregnancy levels.

What Happens to Deep Sleep During Pregnancy?

Pregnancy often leads to less deep sleep, particularly as it progresses into the third trimester. This is mainly because of physical discomforts like a growing belly and frequent bathroom trips, as well as hormonal shifts that can disrupt sleep patterns. Studies show deep sleep, crucial for healing and energy, might drop by around 13 minutes per night in the third trimester compared to earlier, leaving you feeling less rested.

Tips for Better Sleep

While you can’t fully prevent the reduction, try these tips: maintain a regular sleep schedule, use a pregnancy support pillow for comfort, practice relaxation like deep breathing, and avoid caffeine. These can help improve overall sleep, potentially supporting what deep sleep you do get.

Exploring How Pregnancy Affects Deep Sleep

Deep sleep, also known as slow-wave sleep or stage 3 non-rapid eye movement (NREM) sleep, is characterized by slow delta brain waves and is essential for physical restoration, memory consolidation, and cognitive function. It typically constitutes 15–25% of total sleep time, or about 1.5–2 hours for adults sleeping 7–9 hours nightly (How Much Deep, Light, and REM Sleep Do You Need?). Pregnancy, a transformative period involving significant physical and hormonal changes, can impact sleep, particularly deep sleep, due to discomfort, hormonal shifts, and increased awakenings. This analysis examines how pregnancy affects deep sleep, exploring the mechanisms, scientific evidence, individual variations, and practical implications, supported by research and observations as of February 28, 2025.

Defining Deep Sleep and Pregnancy’s Impact

Deep sleep is defined as stage 3 NREM sleep, where brain activity slows significantly, with delta waves dominating, making up about 15–25% of total sleep time, or approximately 1.5–2 hours for adults sleeping 7–9 hours nightly (Sleep: What It Is, Why It’s Important, Stages, REM & NREM). It’s the stage where the body focuses on tissue repair, growth hormone release, and immune system support, with insufficient deep sleep linked to fatigue, memory issues, and increased chronic disease risk.

Pregnancy brings about numerous changes that can disrupt sleep, including physical discomfort from the growing fetus, hormonal fluctuations, and increased frequency of awakenings due to urinary needs or fetal movements. These factors can reduce the amount of time spent in deep sleep, particularly in the later stages, leading to non-restorative sleep and potential health impacts for both mother and baby.

Scientific Evidence on Pregnancy and Deep Sleep

Research suggests pregnancy can reduce deep sleep, especially in the third trimester, due to physical discomfort and hormonal changes. A study titled “Polysomnographic sleep in the first and third trimesters of pregnancy in low-risk women,” published in the Journal of Clinical Sleep Medicine, used polysomnography to measure sleep stages and found that pregnant women in their third trimester had less slow-wave sleep compared to the first trimester and non-pregnant controls (Polysomnographic sleep in the first and third trimesters of pregnancy in low-risk women). Specifically, the study reported that the percentage of slow-wave sleep decreased from 18.4% in the first trimester to 15.6% in the third trimester, translating to a reduction of about 13 minutes of deep sleep per night for an 8-hour sleep period (28,800 seconds, with 18.4% being approximately 5,300 seconds or 88 minutes in the first trimester, and 15.6% being about 4,493 seconds or 75 minutes in the third trimester).

Another study, “Sleep in the first and third trimesters of pregnancy: a polysomnographic study,” published in PubMed, confirmed these findings, noting a significant reduction in slow-wave sleep in the third trimester, attributed to increased arousals and awakenings (Sleep in the first and third trimesters of pregnancy: a polysomnographic study). This reduction is likely due to physical discomforts like fetal movements, back pain, and frequent urination, which fragment sleep and prevent transitions to deeper stages.

Hormonal changes also play a role, with elevated progesterone and estrogen levels during pregnancy affecting sleep architecture. A review from Sleep Medicine Reviews discusses the role of hormones, stating that progesterone, while having a sedative effect, can lead to more frequent arousals and less deep sleep, potentially reducing slow-wave sleep (The effects of exercise on sleep quality in pregnant women: a systematic review and meta-analysis). This hormonal influence, combined with physical factors, contributes to the observed reduction in deep sleep.

Mechanisms of Impact

The reduction in deep sleep during pregnancy can be attributed to several mechanisms:

Physical Discomfort: As pregnancy progresses, especially in the third trimester, the growing fetus can cause discomfort, leading to more frequent awakenings. This includes back pain, leg cramps, and the need to change positions, all of which can disrupt sleep continuity and reduce deep sleep. Fetal movements, particularly in the third trimester, can also cause arousals, fragmenting sleep cycles.
Hormonal Changes: Increased levels of progesterone and estrogen can alter sleep patterns. Progesterone, known for its sedative effects, might help with falling asleep, but it can also lead to more light sleep and frequent awakenings, reducing the time spent in deep sleep. Estrogen fluctuations can affect sleep regulation, potentially contributing to sleep disruptions.
Frequent Urination: The increased need to urinate, especially in the third trimester due to pressure on the bladder, can lead to multiple awakenings, reducing the continuity of sleep and the amount of deep sleep achieved. This is a common complaint among pregnant women and can significantly impact sleep quality.
Stress and Anxiety: Pregnancy can bring about stress and anxiety, which can keep the mind active, preventing transitions to deeper sleep stages. Research indicates that stress can lead to difficulty falling asleep and staying asleep, keeping individuals in lighter stages, which reduces deep sleep and contributes to feeling tired (Stress and Sleep).

These mechanisms collectively contribute to the reduction in deep sleep, particularly in the later stages of pregnancy, with the third trimester being the most affected due to the cumulative impact of these factors.

Individual Variability and Stages of Pregnancy

It seems likely that pregnant women experience about 13 fewer minutes of deep sleep per night in the third trimester compared to the first, based on the polysomnographic studies. However, individual experiences can vary, with some women maintaining better sleep quality depending on factors like overall health, stress levels, and specific pregnancy-related issues. For example, women with low-risk pregnancies might have less disruption compared to those with complications, though the studies focused on low-risk women.

The first trimester often shows similar amounts of deep sleep to non-pregnant controls, with minimal disruption, as physical changes are less pronounced. The second trimester might see some reduction, but it’s the third trimester where the impact is most significant, with studies showing a clear decline. This stage-specific variation highlights the progressive nature of sleep disruption during pregnancy, with deep sleep being particularly vulnerable in the later stages.

Practical Implications and Tips for Improving Sleep

While there’s no guaranteed way to fully restore deep sleep to pre-pregnancy levels, pregnant women can take steps to improve overall sleep quality, which might indirectly support deep sleep. Here are some detailed tips:

Maintain a Regular Sleep Schedule: Go to bed and wake up at consistent times each day to regulate your body’s internal clock, potentially preserving deep sleep. This can help mitigate the impact of irregular schedules, as seen in Sleep Hygiene.
Create a Sleep-Friendly Environment: Ensure your bedroom is dark, quiet, and cool (around 60–67°F) to enhance deep sleep. Use comfortable mattresses and pregnancy support pillows to alleviate discomfort, reducing awakenings. Bringing familiar items, like your own pillow, can also help, reducing the first-night effect.
Practice Relaxation Techniques: Engage in activities like deep breathing, meditation, or prenatal yoga for 10–20 minutes before bed to calm the mind. Studies show meditation can increase slow-wave sleep, supporting deep rest (Meditation and Its Regulatory Role on Sleep). This can help reduce pregnancy-related stress, which disrupts deep sleep.
Limit Caffeine and Alcohol: Avoid caffeine and alcohol, especially in the afternoon and evening, as they can disrupt sleep cycles. Caffeine can delay sleep onset, reducing deep sleep (Caffeine and Sleep), and alcohol reduces deep sleep, with studies showing a decrease in slow-wave sleep after consumption (Alcohol and Sleep).
Stay Active: Engage in regular, moderate exercise, such as walking or swimming, but avoid intense workouts close to bedtime. Research indicates moderate aerobic exercise can increase slow-wave sleep, essential for deep rest (Exercise improves the quality of slow-wave sleep by increasing slow-wave stability). This can help tire the body, facilitating deeper sleep.
Manage Discomfort: Use pregnancy support pillows to find a comfortable sleeping position, often on the left side to improve blood flow, which can reduce awakenings and support better sleep quality. Avoid heavy meals before bed to prevent heartburn, which can disrupt sleep.
Seek Medical Advice: If sleep problems persist, consult your healthcare provider for possible interventions or to rule out any pregnancy-related complications that might be affecting sleep, such as restless leg syndrome or sleep apnea, which can further reduce deep sleep.

An interesting detail is that while sleep position, like sleeping on the left side, can improve overall comfort, there’s limited specific research on how it directly affects deep sleep stages, suggesting it’s more about reducing awakenings than enhancing deep sleep itself.

Age-Specific Considerations and Needs

Age, in the context of pregnancy, is less relevant, but parity (number of previous pregnancies) might influence sleep. First-time mothers might experience more anxiety, potentially affecting deep sleep, while multiparous women might adapt better, though studies are limited. Individual responses vary, with those with high-risk pregnancies potentially seeing larger reductions in deep sleep, highlighting the need for personalized strategies.

Comparative Analysis with Non-Pregnant Sleep

Compared to non-pregnant sleep, pregnant women, especially in the third trimester, have significantly less deep sleep, with studies showing a 2.8% reduction in percentage compared to controls. This difference underscores the need for targeted sleep strategies during pregnancy, with the tips provided aiming to mitigate disruptions and preserve deep sleep as much as possible.

To illustrate, here’s a table summarizing the impact and tips:

Aspect	Impact on Deep Sleep	Tips to Improve	Supporting Evidence
Physical Discomfort	Increases awakenings, reduces deep sleep	Use pregnancy support pillows, find comfortable position	Polysomnographic sleep in the first and third trimesters of pregnancy in low-risk women
Hormonal Changes	Alters sleep architecture, reduces deep sleep	Practice relaxation techniques, manage stress	The effects of exercise on sleep quality in pregnant women: a systematic review and meta-analysis
Frequent Urination	Fragments sleep, reduces deep sleep	Limit fluids before bed, use bathroom before sleep	Sleep in the first and third trimesters of pregnancy: a polysomnographic study
Stress and Anxiety	Keeps in lighter stages, reduces deep sleep	Engage in meditation, maintain routine	Stress and Sleep

This table highlights the variability and underscores the multifaceted approach needed for better deep sleep during pregnancy.

Conclusion

Research suggests pregnancy can reduce deep sleep, especially in the third trimester, due to physical discomfort and hormonal changes, with studies showing about 13 fewer minutes per night compared to the first trimester. It seems likely that individual variations exist, with some women maintaining better sleep quality, and the evidence leans toward no guaranteed way to fully restore deep sleep to pre-pregnancy levels, though tips like using support pillows and relaxation techniques can help. This comprehensive understanding, drawn from recent health literature, underscores the importance of managing sleep during pregnancy for maternal and fetal health.