As labor approaches, your body starts to prepare itself for the task ahead and you may notice various physical symptoms and signs that labor is about to start. Not every woman experiences labor in the same way, and certain signs can occur either before labor starts or during labor.
Toward the end of your pregnancy, you may experience a sensation of building pressure or cramping in your pelvic or rectal area. This pelvic cramping can feel very similar to monthly menstrual cramps. A dull pain in your lower back that comes and goes is common too. You may also notice an increase in heartburn (acid reflux) and gassiness. Unless you have a high-risk pregnancy, there is no need to go to the hospital or call your doctor if you experience any of these symptoms in the later stages of your pregnancy.
This is a time of waiting and many women busy themselves with household tasks. These bursts of activity are often thought to be instinctual, as the mother prepares the home for the new arrival, referred to as "nesting." The anticipation of what will happen during labor can give rise to a mixture of emotions, from fear and anxiety to excitement and impatience. Women may feel fearful about how much pain they will feel or how uncomfortable they will be with bodily functions. Nothing can prepare you fully for how you will feel in labor, but the more you understand about pain relief options beforehand, the more confident you will feel about your ability to manage. It's also thought that by being informed and prepared, you are likely to reduce your anxiety during labor, which in itself can enable you cope better with the pain of contractions.
One of the most common symptoms of approaching labor is an increase in the strength and frequency of Braxton Hicks', or practice, contractions (see False labor), which may be occurring up to four times an hour. The purpose of these practice contractions is to prepare your uterus to deal with real labor contractions so that labor progresses smoothly. Some women find Braxton Hicks' relatively painless, while others find these practice contractions fairly uncomfortable, especially if the baby is quite low and contractions cause increased pelvic pressure.
Apart from the level of pain, one of the main ways to distinguish Braxton Hicks' from real contractions is that Bracton Hicks' are irregular and they fade away, whereas labor pains occur at regular intervals and gradually become stronger, more intense, and closer together. The other main difference between Braxton Hicks' contractions and real ones is that, unlike Braxton Hicks', real contractions cause your cervix to dilate, which indicates that labor is beginning.
No one is sure exactly what triggers labor, but it seems the process varies with each species.
In sheep, a drop in progesterone signals the start of labor. In mice, babies release proteins to signal their maturity, which in turn triggers labor. In humans, little is known about the signals that start labor although there are many theories. Studies suggest that the production of hormones such as corticotrophin-releasing hormone (CRH) by the uterus and placenta may play a role. It's also thought that an increase in pro-inflammatory substances known as cytokines may be involved. Whatever the trigger, it's likely that the onset of labor involves a biological communication between your baby and your body to indicate that your baby is ready to be born.
As you approach labor, you will experience irregular contractions; these will increase in strength and regularity as labor progresses.