How Does Your Body Know When to Go Into Labor?

Labor can feel like a pretty mysterious thing—and when you're a first-time parent, it’s normal to be apprehensive about the whole ordeal. Many people wonder how their body will know it’s time to go into labor, and what that will look and feel like for them.

Every pregnant person is different—and every labor is different, even from one pregnancy to another. But there are some basic facts to know about how labor works, how the body prepares for it, and how your baby “knows” it’s time. Here's what the experts have to say.

How Does Labor Work?

Labor may seem simple, but it’s actually a pretty complex process. “A baby needs to be maneuvered through the pelvic bones and birth canal, and since a human fetus (or newborn) is relatively large compared to our pelvic openings, it takes a lot of work," says Lisa Richards, MSN, CNM, certified nurse midwife and manager of the women's and family health nursing team at Ovia Health

During labor, most work is done by the uterus during contractions, but it’s also done by the person giving birth—and some of it is even done by the baby, notes Richards.

Typically, labor is divided into three stages:

• Stage One: This marks the beginning of labor. It ends when the cervix (the top of the birth canal and entrance to the uterus) is fully dilated (open) and effaced (stretched and thinned).
• Stage Two: Beginning with the full dilation of the cervix, stage two ends when the baby is delivered.
• Stage Three: The third stage starts after delivery and ends after the placenta is expelled.

Some physicians say that there’s also a fourth stage of labor, says Ruth O. Arumala, DO, MPH, a board-certified OB-GYN and co-chief medical officer at Zuri Fertility. “There's some controversy about the fourth stage of labor, which some consider to begin after the delivery of the placenta,” she explains. “During this phase, there's repair of vaginal lacerations or tears.”

Common Signs of Labor

The most common sign of labor is uterine contractions, says Ellen Smead, CNM, certified nurse-midwife at Pediatrix Medical Group in Atlanta, Georgia. These contractions may be light at first and resemble menstrual cramps. But as time goes on, they become stronger and more frequent.

Besides those contractions, you may also notice your water breaking, says Smead. The timing of your water breaking (i.e. the amniotic sac leaking amniotic fluid) can vary from one person to another, with some noticing it early on, some noticing it later, and others never experiencing it. The amount of water you leak also varies.

“There can be a gush or dripping of amniotic fluid that signals rupture of amniotic fluid membranes which house the baby,” says Dr. Arumala. “Usually labor ensues within 24 hours of rupture of membranes even when this happens prematurely.”

Of course, contractions and water breaking aren’t the only signs of labor. “There are a few subtle signs that might mean that labor will be approaching soon, but not everyone notices these symptoms,” says Richards. These can include the passing of your mucus plug and feeling like your baby has “dropped” further into your pelvis.

Some people also experience emotional signs of labor, says Richards. You may notice “nesting” behavior, which may look like having a sudden urge to vacuum the whole house, she says. Other people end up feeling notably more withdrawn before labor begins.

What Causes Labor to Start?

According to the American College of Obstetricians and Gynecologists (ACOG), no one knows for sure what triggers labor. Moreover, the causes of labor are complex and multifactorial. “Labor isn’t initiated by any single factor, like a light switch turning on,” says Richards. “It’s controlled by the interaction of a number of things within the pregnant body.”

In the birthing parent, labor initiation is controlled largely by hormones, and these hormonal changes happen gradually, over the few weeks before you give birth. “One of these changes includes a shift in certain chemical receptors in the cervix," describes Richards. “For most of the pregnancy, the cervix’s job is to remain shut, keeping a growing baby inside. But when labor begins, it needs to soften and be ready to open, allowing the baby out."

There are theories, too, that the fetus plays a role in getting labor started. “When a fetus matures enough, it sends out certain chemical signals to tell the mother’s body that it’s ready to be born,” says Richards. These signals, along with the pressure of a full-term baby on the cervix, may tell the birthing parent’s body that it’s time to get labor started.

How Does Your Body Prepare for Labor?

So what exactly happens as your body gets ready for labor? It's all about your hormones. “The body prepares for labor by beginning to release prostaglandin, as well as the hormone relaxin,” says Smead. Prostaglandins help soften the cervix and get contractions started. Relaxin loosens the pelvis, and it also prepares the cervix for delivery.

Another important way that your body prepares for labor is getting your baby into an optimal position for delivery. “Ideally, your baby also gets ready for labor by getting into the right position,” says Richards. “For the smoothest labor process and the best fit through the pelvis, a baby should be head-down in the pelvis, facing toward your back.”

When to Call Your Health Care Provider

You should get in touch with a health care provider if you think you're going into labor. The first signs of labor can be confusing since it’s common to have "false" contractions (called Braxton Hicks contractions) for weeks beforehand. Unlike true labor contractions, they don't follow a pattern, don't become closer together, and may stop when you move around. Braxton Hicks contractions also don't result in cervix dilation.

Additionally, you should call a provider if you're concerned something isn’t quite right with your pregnancy. According to Richards, warning signs of pregnancy emergency include:

• Heavy vaginal bleeding
• A hard, firm abdomen that doesn’t soften between contractions
• Severe abdominal pain
• Leaking discolored or foul-smelling amniotic fluid
• Fevers
• Severe headaches and vision changes
• Lack of movement from the fetus
• Trouble breathing
• Chest pain