The science of sleeping in pregnancy

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by Professor Colin Espie

On average, national surveys suggest that pregnant women typically sleep for an extra hour per night, but there are big differences over the nine months.

First trimester

The growing fetus is very small, but it is developing rapidly and requires a lot of energy. Even though you may be sleeping for longer, it's still normal to feel tired – high levels of the hormone progesterone increase both daytime sleepiness and your need for sleep. Progesterone also causes you to produce more urine. As your enlarged uterus presses on the bladder, you are likely to get up more often during the night to go to the bathroom.

Second trimester

Sleep often returns towards normal as development of the fetus slows, and the uterus changes position to above the bladder. Restless sleep and sleep complaints increase towards the start of the third trimester.

Third trimester

The heavier, rapidly growing fetus requires a lot more energy and it's normal to feel fatigued. Many women also suffer back ache and discomfort, as well as feeling kicking and moving at night. Leg cramps are common, probably caused by low calcium and potassium levels. Many women complain that they wake frequently and find it difficult to get back to sleep. Frequent trips to the bathroom are normal, partly due to higher overnight sodium release. The hormone oxytocin can add to more fragmented sleep. As pregnancy progresses, women are at higher risk of developing sleep disorders such as restless legs syndrome, breathing-related sleep problems such as snoring and sleep apnea, and insomnia.

Consequences of short sleep in pregnancy

It is increasingly clear from the scientific literature that whether or not you're pregnant, sleep plays a crucial role in emotional control, cognition and physical health. The US National Sleep Foundation recommends 7 to 9 hours sleep every night for the average (non-pregnant) adult to maintain optimal health. When you're pregnant, how you feel is the best guide to how much sleep you need – if you're persistently sleepy during the day, try to make time for one or more short naps during the day, or for extra hours of sleep during the night.

Some research suggests that women who sleep for fewer than 5 or 6 hours throughout pregnancy have higher risks of problems related to high blood pressure, depression and cesarean deliveries than women who sleep for 7 hours or more. However, the mechanisms are not well understood and there is no simple cause and effect relationship. If you're worried about your sleep at any time during your pregnancy, speak to your healthcare professional.

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