Sleep, Hormones, and Pregnancy

So you found out recently that you’re pregnant, but now you’re sleepy throughout the day, and yet having trouble falling asleep at night? Could it be the excitement? Thinking about the baby that you’ll have in several months, maybe you stay up late thinking of names. Well, if that is the case, probably it doesn’t have much to do with why you don’t sleep. Does insomnia (having trouble falling asleep or staying asleep) have something to do with why you get sleepy during the day? Absolutely. But the reason is not only because of the quantity of sleep; it’s also the quality. It has to do with hormones and how they affect sleep physiology.

Let’s run through the basics. Sleep is a normal function in most animals. Birds, fish, and mammals (which include humans) all do it. It helps the body to grow new tissue, to repair damage, and to rest. Sleep occurs in stages. Stages 1, 2, and 3 are known as non-REM, or NREM, sleep. The other stage is rapid eye movement, or REM sleep. This is the stage during which most dreaming takes place. The stages occur in a cycle, with 1,2,3, and REM cycling through the night, the amount of time in REM sleep increasing with each cycle.

Pregnancy is one of the times when the body does a great deal of growing. Pregnant or not, if you lose some sleep, you can function, drink coffee to compensate, and make up for the loss over the next night or two. But sleep deprivation day after day makes you sick, and extreme deprivation of sleep even can lead to death. Various studies published between 2007 and 2010 have demonstrated an association between lack of sleep and hypertension -high blood pressure- a major risk factor in heart disease and strokes, the first and third leading causes of death, respectively, in the United States.

Generally, six hours per night is cited as the minimum amount of sleep that most adults need to remain healthy. It is clear that many people need somewhat more than this; it is not so clear that people who claim that five hours per night is enough for them are correct. Most sleep experts agree that if you are pregnant you should get closer to eight hours. That is, if you can. Upon learning of their pregnancy usually a few weeks into the first trimester, many women find that they are not sleeping as well as they did before.

The reason for this is hormonal. During a normal menstrual cycle, the hormones estrogen and progesterone rise and fall in a certain pattern, both hormones being at a low at menstruation. If fertilization takes place, then of course you do not menstruate, but then what happens is that the levels of both hormones begin to rise and climb throughout pregnancy. The interplay between the various hormones and sleep is complex and not understood completely, but a lot is known.

Having a lack of estrogen, for example, is known to contribute to a disorder called sleep apnea, a condition in which breathing is interrupted frequently while sleeping, which also interrupts sleep so that the person doesn’t sleep well and is sleepy during the day. Progesterone seems to promote sleep, suggesting that women actually should sleep better as the levels rise throughout pregnancy. Why is this not the case? It turns out that while progesterone makes a woman sleepy in general, it actually may decrease the amount of REM sleep, so that the overall quality of sleep suffers. The implication is that pregnant women would not dream as much as perhaps they ought to dream.

But there is another hormone involved and that is melatonin. Unlike estrogen and progesterone, melatonin is present in women as well as men. We all use it to go to sleep. It comes from the pineal gland in the brain and its release pattern depends of the cycles of light and darkness. These cycles are known as circadian rhythms. When it gets dark at night, your pineal gland begins to send melatonin coursing through your blood stream. This makes you sleepy and keeps you asleep throughout the night. The only problem is that, in modern society, often we interrupt circadian rhythms when we fly quickly between multiple time zones, and also when we keep the lights on late into the night. Not only does this make it more difficult to fall asleep but seems to have been a factor at play in the increased incidence of certain cancers during the 20th century as the use of electric light bulbs increased.

Keeping the lights on at night in the hour or two before you go to bed prevents your pineal gland from releasing melatonin to put you to sleep. While the increased progesterone of pregnancy may help you to feel sleepy and may induce non-REM sleep, it also increases your need to urinate, thus waking you up. If you turn the lights off and thus get your melatonin turned on, it doesn’t take much to turn it off. Turning on a light, for instance to go to the bathroom, even for a couple of minutes, can stimulate your pineal gland to shut off. While this can be helpful in the morning so that the light wakes you up, in the middle of the night it can mean trouble.

Studies have shown that it can take a long time to turn your melatonin back on in the middle of the night once exposure to a small amount of light signals the pineal gland to turn it off. On the other hand, it turns out that not all light turns off your melatonin. Only light at wavelengths less than about 520 nanometers or so -light in the blue and partly into the green part of the light spectrum- turns it off. This means that the price of keeping you melatonin up throughout the night is not having to bump into walls or having to feel your way around in the dark go to the bathroom. It simply means that you need only avoid the blue-green light at night (and avoid white light, which includes all of the colors), replacing it with red light, yellow light, or orange light in the bathroom or wherever you may need to go in the middle of the night.

Since melatonin not only helps you to go to sleep but -unlike progesterone- also helps to increase REM sleep, working on keeping the level of this hormone up during the night may also help to assure that your sleep is full of happy dreams.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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