Pregnancy insomnia is driven by a combination of hormonal shifts, physical discomfort, and psychological changes that intensify as pregnancy progresses. About 37% of pregnant women experience poor sleep quality in the first trimester, rising to 48% in the second and 60% in the third. The causes shift depending on where you are in pregnancy, but they tend to layer on top of each other rather than replace one another.
How Pregnancy Hormones Disrupt Sleep
The same hormones that sustain a healthy pregnancy also interfere with sleep. Progesterone and human chorionic gonadotropin (hCG) are both soporific, meaning they promote drowsiness. That sounds helpful, but the effect is paradoxical: progesterone makes you sleepy during the day while fragmenting your sleep at night. You may fall asleep faster in the evening only to wake up repeatedly and struggle to stay asleep.
Estrogen adds another layer. Both estrogen and progesterone suppress REM sleep, the phase most associated with dreaming. This suppression is strongest in early pregnancy when hormone levels are climbing rapidly. As pregnancy continues and your body adjusts, REM sleep can rebound, which may partly explain why vivid dreams and nightmares become more common later in pregnancy. Those intense dreams can wake you up and make it harder to fall back asleep.
Rising estrogen and progesterone also influence your breathing regularity and the overall architecture of your sleep cycle, meaning the way your body transitions between light sleep, deep sleep, and REM. Even when you’re technically sleeping enough hours, the quality of that sleep can be noticeably worse.
Physical Discomfort by Trimester
First Trimester
In early pregnancy, the physical causes are mostly hormonal rather than mechanical. Your body isn’t much bigger yet, but nausea can keep you awake at night despite its misleading name “morning sickness.” Frequent urination also starts early because rising hCG levels increase blood flow to your kidneys, and progesterone relaxes your bladder muscles. You may find yourself getting up to pee two or three times a night well before your uterus is large enough to press on your bladder.
Second Trimester
Many women get a partial reprieve in the second trimester as nausea fades and hormone levels stabilize somewhat. But new discomforts start creeping in: heartburn, leg cramps, and round ligament pain (a sharp or aching sensation in your lower belly as the ligaments supporting your uterus stretch). Back pain often begins here too, as your center of gravity shifts forward.
Third Trimester
The third trimester is when insomnia peaks, and the reasons are largely mechanical. The weight of a growing baby puts pressure on your joints, back, and bladder simultaneously. Finding a comfortable position can take ages. Once you finally settle in, the urge to urinate may pull you out of bed again. Shortness of breath becomes more common as the uterus pushes up against your diaphragm. A faster resting heart rate, Braxton Hicks contractions, and an active baby who seems to prefer nighttime gymnastics all contribute. Many women describe a frustrating cycle: exhaustion during the day but an inability to stay asleep at night.
Restless Legs and Iron Deficiency
Nearly one-third of pregnant women develop restless legs syndrome (RLS), an uncomfortable urge to move the legs that worsens at rest and tends to strike at bedtime. The condition is strongly linked to iron deficiency. Studies have found that pregnant women with RLS symptoms have significantly lower hemoglobin levels and signs of iron-deficient anemia compared to those without symptoms, and the severity of RLS correlates directly with how low hemoglobin drops.
What makes this especially frustrating is that even women who are taking oral iron supplements can still develop RLS if their bodies aren’t absorbing enough iron to keep up with the demands of pregnancy. If you’re experiencing creeping, crawling, or aching sensations in your legs at night, it’s worth having your iron levels checked rather than assuming it’s just a normal pregnancy discomfort you have to endure.
Breathing Changes During Sleep
Pregnancy changes your airway in ways that can disrupt breathing during sleep. Increased blood volume causes the tissues lining your nose and throat to swell, narrowing the space air flows through. At the same time, your lungs have less room to expand as the uterus grows, and your body’s oxygen demand increases. These changes can produce or worsen snoring and, in some cases, lead to obstructive sleep apnea, where the airway repeatedly closes during sleep and your body wakes you up to resume breathing.
Pre-pregnancy obesity and excess gestational weight gain raise the risk, but the airway swelling and fluid shifts of pregnancy mean even women who never snored before can develop sleep-disordered breathing. Each partial awakening may be too brief to remember, but the cumulative effect is fragmented, unrestorative sleep. Women with pregnancy-related high blood pressure are at particular risk because the associated fluid retention can further narrow the airway.
Blood Sugar and the Stress Response
Disrupted sleep and blood sugar regulation feed into each other during pregnancy. When sleep is fragmented, your body releases more cortisol, the primary stress hormone. Cortisol regulates fat and glucose metabolism, and prolonged elevation makes your cells less responsive to insulin. This can raise blood sugar levels, which in turn triggers inflammation that further disrupts sleep quality, particularly deep sleep.
This creates a cycle: poor sleep raises cortisol, which raises blood sugar, which promotes inflammation, which makes sleep worse. The relationship is bidirectional, meaning women who develop gestational diabetes are more likely to have sleep problems, and women with severe sleep disruption are more likely to develop glucose intolerance. You don’t need to have gestational diabetes for this cycle to affect you. Even moderate sleep fragmentation can nudge the stress-hormone system into a pattern that makes restful sleep harder to achieve.
Anxiety, Worry, and Dream Changes
Psychological factors are among the most underestimated causes of pregnancy insomnia. Worries about the baby’s health, labor, finances, and the transition to parenthood can keep your mind racing at bedtime. This type of cognitive arousal, where you can’t “turn off” your thoughts, is one of the most common triggers for difficulty falling asleep.
Dream content also shifts during pregnancy. Research suggests that dream recall increases as pregnancy progresses, and the themes tend to reflect waking concerns: fears about the baby, anxiety about childbirth, worries about being a good parent. Some researchers believe this serves a psychological function, essentially rehearsing responses to perceived threats. But the practical result is that vivid or disturbing dreams wake you up and leave you emotionally activated, making it harder to return to sleep. Poor sleep quality and insomnia in late pregnancy have been shown to increase nightmare frequency, adding another self-reinforcing loop.
What Helps and What’s Uncertain
Because pregnancy insomnia has so many overlapping causes, there isn’t a single fix. Sleep hygiene basics still apply: keeping your bedroom cool, maintaining a consistent bedtime, and limiting screen time before sleep. A pillow between your knees or under your belly can ease pressure on your back and hips in the third trimester. Sleeping on your left side improves blood flow and can reduce some of the discomfort from a heavy uterus pressing on major blood vessels.
For restless legs, checking your iron and ferritin levels is a practical first step. Gentle stretching before bed and avoiding caffeine can also reduce symptoms. Heartburn improves for many women by eating smaller meals earlier in the evening and propping the head of the bed up slightly.
Melatonin supplements are worth addressing because many women wonder about them. Clinical trials that have used melatonin during pregnancy for various conditions haven’t raised major safety concerns, but there are no randomized controlled trials specifically testing melatonin for pregnancy insomnia. The evidence is too thin to draw firm conclusions about either safety or effectiveness for sleep in pregnancy. Cognitive behavioral therapy for insomnia (CBT-I), which restructures the thought patterns and habits that perpetuate sleeplessness, has the strongest evidence base for insomnia in general and carries no medication-related risks.