Now that you’re pregnant, you’re dutifully attending your childbirth classes, reading and viewing everything you can about the stages of labor and birth. But there’s a lot that nobody tells you about labor because experiencing it is different from hearing about it. Classes, books, online resources, friends and family can give you the big picture about labor. But the surprising — and sometimes embarrassing — details of your childbirth scenario will be all your own. You may sail through, or you may strip.

 “I’ve had patients who were so uncomfortable that they pulled off their gowns and delivered naked,” says Lisa Fraine, a certified nurse-midwife. These reactions are common; they’re simply a response to pain and exhaustion. You can also blame hormones: “Labor causes a shift in your estrogen and progesterone levels, which is akin to a major case of PMS,” says Henry Klapholz, M.D.

If you do lose it, don’t feel bad. Doctors and nurses are used to these reactions. But if you’re uncomfortable with the idea of such a display, be prepared for your delivery. “Women who take childbirth classes tend to stay calmer than those who don’t,” Klapholz acknowledges.

Because knowing what to expect makes for a less stressful delivery, we’ve asked the experts to spill the beans on more common (yet seldom-talked-about) scenarios.

You become nauseous and may even throw up.

Many women think that vomiting during labor is abnormal, but it’s not. One reason it happens: Epidurals can cause hypotension, a sudden drop in blood pressure.

“An early sign of this is nausea and vomiting,” says David Birnbach, M.D., past president of the Society for Obstetric Anesthesia and Perinatology.

But throwing up can occur even if you haven’t been given an epidural, either because of the pain you’re experiencing or as a result of food sitting in your stomach (digestion usually stops during labor). To keep vomiting to a minimum, eat only light foods during the earliest stages of labor, and stop eating completely — and drink only clear liquids — once you’re in active labor.

Your teeth chatter.

Nearly 50 percent of women complain of shivering and teeth chattering,” Birnbach says. It has nothing to do with being cold. In fact, your body temperature may rise a degree or two during labor, making you feel hot. The jury’s still out on what exactly causes this, but the latest evidence points to blood incompatibility.

“During labor, a small amount of fetal blood crosses into the mother’s bloodstream,” Klapholz says. “Studies show that when there’s an incompatibility in blood type between mother and baby — for example, your blood is type A and your baby’s is type B — the mother shakes, shivers and get chills.”

You make noises.

As a baby descends through the birth canal, air gets forced out the anus, so be prepared to pass gas. This is especially likely if you’ve had an epidural, which paralyzes the anal sphincter.

Another unpleasant side effect of childbirth: You may have a bowel movement right on the delivery table.

“It’s purely a space issue,” says Arianna Sholes-Douglas, M.D., a high-risk pregnancy obstetrician. “As your baby’s head makes its way through the birth canal, the rectum gets flattened and its contents pushed out.” In any event, don’t worry. “These bodily functions happen all the time — there’s very little we haven’t seen or heard before,” says registered nurse Deborah Robbins.

Your mind goes blank.

In the heat of the moment, it can be easy to forget what they taught you in childbirth class.

“I couldn’t remember the various positions I was supposed to get into to ease labor pains,” says new mom Elizabeth Estes Niven. “Instead, I stayed flat on my back, gripping the bed railing,” she adds.

You’re also likely to forget many of the details of the birth. So be sure your partner takes plenty of photos or captures it all on video.

It may not be love at first — but most likely it will be.

Don’t feel bad if your first reaction to holding your newborn isn’t overwhelming joy. You’ve just been through an exhausting experience and need time to recover. If you can, try breastfeeding — then let a nurse take your child so you can get some rest. That’s what I did after 17 hours of labor and a C-section. But after an hour, I had them bring my baby girl back and I was immediately smitten!