That pregnant women have strange and more vivid dreams might sound like a myth, but it's an actual phenomenon. It's also something of a mystery as to why it happens.

The first thing to do with any pop psychology phenomena is investigate if it's even real. In this case, it's clear from the sheer amount of anecdotal evidence that this is actually something women experience:

• The American Pregnancy Association states: "Some pregnant women have reported having a change in their dream state during sleep as a result of pregnancy."
• WebMD has a feature article, "The Vivid Dreams of Pregnant Women," which posits that all types of dreams are more common during pregnancy.
• Psychology Today also goes in-depth: "Why Pregnant Women Have Bizarre Bad Dreams."

As with almost every aspect of pregnancy, each woman's experience with dreams while carrying a baby is different.

According to the sources above, many women report an increase in how vivid and intense their dreams are, how well they remember them, and how often they happen. 

A common theme of pregnancy dreams seems to be not being ready for the baby's arrival. Others report dreams involving animals, water, travel, an unfaithful partner, architecture, disasters, or complications in childbirth. Many of these dreams are actually considered nightmares, and unlike so many other pop phenomena claims, there's some statistical evidence behind the idea that they are more common in late-stage pregnancy.

In 2014, a limited study in the journal Sleep Medicine found that, among pregnant women in their third trimester and a control group, "More pregnant women (21 percent) than non-pregnant women (7 percent) reported a nightmare incidence exceeding moderately severe pathology." It also found that, "Late pregnancy is a period of markedly increased dysphoric dream imagery." A German study carried out a few years included a larger cohort and found that 11 percent of the pregnant women reported vivid nightmares, as opposed to just 2 percent in the control group. 

Just as the subject of dreams differs between pregnant women, it also differs by where a woman is with her pregnancy. In an interview with WebMD, Patricia Garfield, author of the book "Creative Dreaming," noted "dream content changes as a woman's body changes. Her dreams echo her changing condition and both her hopes and her fears about the coming child."

In the first trimester, Garfield said, dreams about water and fertility are common. As the body changes, the dreams become less abstract and more about the baby and what's happening to the woman's body. Finally, the third trimester brings anxiety about the birth and its aftermath, highlighted by the vivid nightmares examined in the German study.

All of this is likely happening for a couple reasons: a massive increase in hormones and more frequently interrupted sleep.

As Parents.com puts it:

"Since pregnant women tend to wake more often throughout the night (as a result of being physically uncomfortable, needing to pee, or because the baby is moving), they experience several interrupted phases of REM sleep, which is when dreams occur [and when] you're a lot more likely to remember your dreams, making them seem more vivid, colorful, and real." 

There's little to be done about pregnancy dreams, other than using them as clues for what's bothering someone in terms of their pregnancy. And if they aren't too nightmarish, embrace them. 

"There are many types of dreams during pregnancy, since it is the highest amount of dreaming that takes place during a woman's life," Garfield told WebMD. "Some of them are even beautiful — dreams about birthdays, or holidays or ceremonies, which may reflect a conclusion or a joyful celebration."