Progesterone: sleepy but not rested
Progesterone rises steeply from early pregnancy. It acts on GABA receptors in the brain, which is why the first-trimester exhaustion is so overwhelming — many mothers describe sleeping ten hours and waking unrefreshed. The catch is that progesterone also reduces the proportion of deep, slow-wave sleep and increases the number of night-time awakenings. So quantity goes up while quality goes down.
It also relaxes smooth muscle everywhere: the bladder wall (more night urination), the gut (reflux and constipation) and the airway (snoring).
Oestrogen: congestion and less dreaming
Oestrogen reduces REM sleep and increases blood flow to the mucous membranes, causing the nasal congestion — pregnancy rhinitis — that affects a large minority of mothers and makes nose breathing difficult at night. It also contributes to fluid retention, which narrows the upper airway and worsens snoring. Saline nasal spray and a humidifier help; decongestant sprays should not be used regularly in pregnancy.
Relaxin: reflux by another route
Relaxin softens ligaments and smooth muscle, including the sphincter at the top of the stomach. Combined with upward pressure from the uterus, this is the mechanism of pregnancy heartburn. It also loosens the pelvic and spinal joints, so lying in one position for hours becomes uncomfortable and you wake to turn more often.
Cortisol and the shifting clock
Cortisol levels rise progressively through pregnancy and the daily rhythm flattens somewhat, which can push your natural sleep timing later and make early waking harder. Melatonin production rises through pregnancy too, and the placenta produces its own. Do not take melatonin supplements in pregnancy — the safety data is inadequate and dosing is unregulated.
Prolactin and the third trimester
Prolactin rises in preparation for feeding and is associated with more frequent, shorter sleep episodes — arguably a rehearsal for the newborn period. Combined with physical discomfort, night urination and Braxton Hicks contractions, third-trimester sleep is genuinely fragmented for most mothers, and total sleep time typically falls.
Trimester by trimester, and what helps
- First trimester: overwhelming sleepiness, more awakenings. Nap early in the day, no later than 4 pm, and no longer than thirty minutes. Do not fight the tiredness.
- Second trimester: usually the best sleep of the pregnancy. Use it to establish a routine and a side-sleeping position before the bump forces it.
- Third trimester: the hardest. Prop the upper body, use a full-length pillow, stretch calves before bed, front-load fluids, and accept a broken night without adding anxiety to it.
What not to reach for
No sleeping tablets, no melatonin, and no herbal sleep supplements without your doctor's approval — several common ones, including valerian and high-dose chamomile extract, lack pregnancy safety data. Antihistamines are sometimes prescribed short-term, but on medical advice only.
Hormonal, but still worth reporting
Loud snoring with gasping or pauses, severe restless legs, insomnia with low mood, night-time itching on palms and soles, or breathlessness at rest. These are not simply hormones — they are specific conditions with specific treatments.