Sleep patterns change during pregnancy. These changes may occur as a result of hormonal fluctuations and physical symptoms, such as frequent urination, anxiety, aches, cramps, heartburn and other discomforts leading to disruptive sleep. This is why we built an algorithm to detect sleep and the breakdown of sleep stages for Apple Watch users - so that you can track what is going on during your pregnancy.

Studies report that in non-pregnant adults, approximately 50% of sleep is light, 20% is deep, 25% is REM (rapid eye movement) and the remaining 5% is active sleep (the transition stage between being awake to falling asleep). This is known to change in different ways at each stage of pregnancy.

In the first trimester of pregnancy, symptoms of fatigue can be quite troublesome, with women tending to sleep longer on average. Studies also report increased wake after sleep onset and reduced sleep efficiency. Increased levels of the hormone progesterone may lead to disrupted sleep and you may notice a decline in the amount of deep sleep and REM sleep.

In trimester two, sleep efficiency tends to improve. You may notice increased energy and improved mood during this time. However, towards the end of the second trimester, Braxton-Hicks contractions or stomach pains may lead to disrupted sleep.

In the final trimester, it is common to experience multiple nighttime awakenings and more lighter sleep. Studies report reduced daytime alertness, more daily naps and symptoms of insomnia in 21% of women. However, the use of sleep medication is typically avoided due to the risk of complications, so pregnant women experiencing sleep difficulties are usually advised to seek non-pharmacological treatment options such as relaxation techniques, CBTI (cognitive behavioral therapy for insomnia), yoga, exercise and the use of pillows to create a more comfortable sleeping position.