You’re about 12 weeks pregnant and suddenly you must have nachos. Lots and lots of nachos. But when you’re standing in line for Mexican food, you realize nothing would go better with nachos than a bowl of strawberries and whipped cream.

Watch out: Your pregnancy cravings are officially in full swing.

Here’s a look at why cravings happen during pregnancy and what they mean. We’ll also discuss how long they last and if it’s safe to indulge.

It’s common during pregnancy to crave odd combinations of food or things you’ve never wanted to eat before.

According to research presented in Frontiers in Psychology, about 50 to 90 percent of American women have some type of specific food craving during pregnancy. But doctors don’t know exactly why pregnant women get the urge for specific tastes, textures, or flavor combinations.

Rapidly changing hormones might be to blame. Cravings might also happen because of the extra work your body does to quickly produce a lot more blood. Or it might be as simple as the comfort certain foods bring as your body changes.

For most women, cravings start in the first trimester, peaking during the second trimester, and declining in the third.

Doctors say that few cravings continue after delivery, so you won’t keep eating the same strange things forever. In fact, a lot of women have one craving for a day or two, another craving for a different day or two, and so on.

Food aversions are the opposite of food cravings. They can create some equally unusual feelings. Food cravings and food aversions during pregnancy usually start around the same time.

Interestingly, Frontiers in Psychology found that food cravings might not have anything to do with the nausea and vomiting of morning sickness, but avoiding certain foods probably does.

Meat, normally a staple for most women in the United States, is often rejected during pregnancy. The sight and smell of raw meat, cooking smells, and the texture of prepared meat can be too much for some pregnant women to stomach.

Research published in 2006 found that women experience much more morning sickness when meat is consumed in larger amounts.

So why is meat such a monster for some? Researchers suspect it’s because meat sometimes carries bacteria that can make a mother and baby sick. The body protects them by making meat an unappetizing option.

Most pregnancy cravings are personal, harmless, and can even be kind of funny. Some of the most commonly reported craved foods in the United States are:

A recent survey conducted by the supplements brand Pregnacare found that chocolate, fruit, and ice pops were among the most commonly craved foods by women in the United Kingdom.

Other cravings reported by individual survey participants included:

For some, odd combinations of food are most satisfying — that’s the root of the famous joke about pregnant women eating pickles and ice cream.

There’s even a cookbook, Pickles and Ice Cream, that features recipes, both bizarre and beautiful, that have been craved by real pregnant women.

French fries, cookies, and bread, oh my!The majority of cravings I see patients having are for carbohydrates — French fries, cookies, breads. Some mention craving foods they haven’t liked before, such as sushi. From a safety aspect, always make sure that if you consume foods such as meat, fish, or sushi, make sure they are fully cooked and advised to be safe in pregnancy. – Holly Ernst, PA-C

Some cravings can be dangerous and a sign that you need to see a doctor. If you have a strong desire to eat dirt, soap, or other nonfood items during pregnancy, you may have pica, a potentially poisonous condition.

While only a small number of women crave alcohol or drugs during pregnancy, the danger to your baby is too great to give in. Talk to your doctor about this to keep you and your baby safe.

Even if you only want French fries for every meal, be sure to pay attention to how many you’re munching on. Most doctors say occasionally giving in to high-salt, high-fat, and high-carbohydrate cravings isn’t a big deal, especially if the cravings only last a short time.

But take note: A steady diet of unhealthy foods that are high in fat, sugar, or chemicals can lead to excessive weight gain, gestational diabetes, or other problems that can last beyond the birth of your baby.