Labor is usually painful for several very good reasons. For one, the cervix, completely insensitive to burning and cauterization, is nevertheless extremely sensitive to pressure and stretching--precisely what it undergoes during labor. Most women feel contractions as cramping sensations in the groin or back, though some experience more pain in their sides or thighs. As the contractions get longer, stronger, and closer together over the course of labor, they will be perceived as more or less painful by different women.
In addition, the uterine muscle--at term, the largest and strongest muscle in your body--may have to work at alternately contracting and relaxing for hour after hour. That can lead to a tired, achy feeling, just the way the voluntary muscles in your arms and legs might feel exhausted and sore after a difficult workout. The normal decrease in oxygen flow to the uterus as it contracts can add to that achy feeling.
During labor a lot of pressure may be exerted on the fallopian tubes, ovaries, and ligaments. The baby's presenting part (usually the head) presses firmly against your bladder and bowel as he descends through your pelvis. This can lead to great pain, particularly if you don't empty your bladder frequently. About once an hour is a good rule to remember.
The rectum usually empties itself ("nature's diarrhea") in early labor. If it doesn't, you may choose an enema to give your baby more room. Whether your rectum is empty or not, the pressure of the baby's head on surrounding nerves will be surprising. This feels as though you are going to have a bowel movement right now. To some women, that feeling of rectal pressure is extremely painful.
When you are in the pushing or second stage of labor, you will probably feel an extraordinary sensation of stretching in your vagina.
Whether or not a woman had had a baby before seemed to make a big difference.
Also, change the meaning of the situation to make it more or less painful. One study, for example, showed that women who had previously experienced high levels of pain unrelated to childbirth reported less labor pain than other women.
The biggest difference among people, however, isn't in their perception of pain but in their ability and motivation to withstand it. In one experiment, for example, Jewish women increased their level of tolerance after they were told that their religious group had a lower pain tolerance than others.
It's well known that a person may have a low tolerance for pain in one situation, but a high tolerance in another. For example, soldiers whose severe wounds would warrant strong painkillers in a civilian population nevertheless denied feeling high levels of pain when they were interviewed away from the battleground. Athletes are often observed to continue playing despite injuries that a non-player probably would find quite painful.
Your pain threshold can also be lowered or raised by the type of attention you focus on a sensation. In one pain experiment, simply reading the word "pain" in the instructions made subjects find a low level of electric shock painful. They didn't report the same level of shock painful when the suggestive word "pain" was left out of the instructions. This, of course, is the reason childbirth teachers refer to "labor contractions" and not to "labor pains."
By the same token, if your anxiety is reduced instead of built up, your pain threshold may be increased. Another pain experiment gave subjects control over the painful stimulus, an electric shock. With a sense of control, subjects found the stimulus less painful, probably because they experienced less anxiety about what would happen to them.
