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What Causes Labor? Science's Best Guess Is: Your Baby

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Scientists know more about pregnancy and birth than ever before. But what causes labor? Turns out, we don't really have a clue yet.

"No one really understands what causes labor," says Martha Artyomenko of Montana's Flathead Valley Doulas in an interview with Romper. And the uncertainty can be anxiety-inducing.

We know how fetuses develop; what they look like at every stage. Geneticists can explain why your baby has green eyes instead of brown or why certain conditions only occur in boys and not girls. Doctors can screen for birth defects in the womb. Heck, they've mapped the entire human genome. But as for labor? A full 22 percent of American mothers are induced, a rate that has more than doubled from 1990 to 2006 per the Centers for Disease Control. Women take it for granted that at least something flicks the switch. But what is it? What’s that magic bullet that causes contractions to start; causes birth to begin?

It’s hard to believe science could be so clueless about such an elemental process. What they do know is that it comes down to two hormones: oxytocin and prostaglandin. When it’s developing, the fetus is floating in a fluid-filled bag called the amniotic sac. Eventually, that sac will rip or tear, and fluid will starts gushing (or trickling, or splashing — it's different for each woman) from the vagina. This is otherwise known as the great rupturing of the membranes — your water breaking. But only 15 percent of women experience their water breaking before labor begins, per The Bump. The rest are likely to worry about their lack of progress, or want to hurry things along.

"Once I passed my due date, and the hot summer weather started, I was ready for the baby to be born. I was ready to try anything," says Lisa Yakomin, a mother of three from New Jersey.

If you go into the hospital to have labor induced, your doctor or midwife will give you pills, IVs, or vaginal suppositories that introduce prostaglandin, the hormone that naturally floods your body when you go into labor. Usually, this enough to start contractions, but if it isn’t, you’ll move onto Pitocin, the name for a synthetic version of the hormone oxytocin. Normally, during later gestation, oxytocin receptors in the uterine smooth muscle cells increase, leading to the uterus getting "irritable." This sounds unpleasant (and it can be when it happens too soon), but it's a good thing when the baby is full-term, because it makes it more likely that contractions will begin.

Physically, it's clear what happens when you go into labor (it’s pretty obvious, especially in the movies, when it always seems to happen in the middle of a grocery store). But where do these hormones come from?

Your healthcare provider can also perform a membrane sweep with a gloved finger, which may also cause the sac to rupture and the prostaglandins to swing into action.

So, physically, it's clear what happens when you go into labor. (In the movies, it always seems to happen like Noah's flood in the middle of a grocery store). But where do these hormones come from? Traditionally, researchers believed that the mother must be the one giving these hormones off from her pituitary gland. Nowadays, however, scientists are starting to suspect it might actually be the baby who kicks birth into action.

Researchers at UT Southwestern Medical Center at Dallas found that a signaling protein, called surfactant protein A, secreted by the lungs of a mouse fetus, causes the mother to produce prostaglandins, which then trigger the contractions.

"It signals to the mother's uterus when the fetal lungs are sufficiently mature to withstand the critical transition to air breathing," Dr. Carole Mendelson, who led the research, said in a press release.

After all, when nobody really knows what causes labor, if your sister’s neighbor’s best friend said that a Chipotle burrito and a foot massage worked for her, who are you to argue?

Another study by the University of Texas, published in the journal PLOS One, noted that certain cell markers appear as a woman starts labor. These are known as telomere fragments, and they show up in the amniotic fluid as the placenta ages, basically acting like a Facebook birthday reminder, telling your baby it’s old enough to be born. "It is linked to the baby's brain producing oxytocin, which in turn triggers our body to produce and cause labor," Martha Artyomenko of Montana's Flathead Valley Doulas explains.

But what if you're 41 weeks pregnant and really just want this whole thing over already? A Google search turns up dozens of DIY tips from birth experts and well-meaning moms, advocating everything from pineapple to black cohosh to a long walk to a good old-fashioned roll in the hay to induce labor. It's no surprise that folk remedies continue to be popular to naturally induce labor. After all, when nobody really knows what causes labor, if your sister’s neighbor’s best friend said that a Chipotle burrito and a foot massage worked for her, who are you to argue?

But "there are no proven non-medical ways for inducing labor naturally," New York midwife Elizabeth Stein, CNM, told WebMD. That means most of what's included on those lists of “X ways to induce labor” you see in your Google results are all anecdotal at best. Like, for instance, that trip to that Mexican taqueria down the street that your cousin swears helped her go into labor.

For instance, Maine mother Maddrey Coover said Velveeta cheese worked for her. "The premise of castor oil is that which makes your stomach cramp causes labor, and Velveeta was historically my stomach's greatest nemesis."

According to Artyomenko, "Spicy food might upset your stomach and sometimes, if baby is ready to go, an upset stomach might irritate the uterus and cause contractions, which can turn into labor," she said, adding, "many people will recommend red raspberry leaf tea, but it is not going to induce labor or really do anything, other than give your uterus valuable nutrients. It is a uterine tonic, not stimulant."

A Google search shows a grab-bag of other herbal methods, such as evening primrose oil. "While sometimes those can work," Artyomenko tells Romper, "some of them are touted as 'natural,' but [they] carry the same risk factors as a pharmaceutical induction. So, if you choose to use a method like with herbs, talk to your care provider and only do [so] under their guidance."

In other words, try at your own risk, because scientifically, the jury is still out.

'[My doctor] told me to have sex. I said, 'HOW?!' I was almost two weeks past my due date by then, and I was huge. She actually gave me a booklet with different positions to try, and lord help me, I took it home and told my husband, 'OK, we're doing this.'

There are a small number of at-home labor induction techniques that have been studied, and acupuncture is one of them. Used for centuries in Asia to help move labor along, researchers at the University of North Carolina found that 70 percent of women who got acupuncture went into labor naturally, compared to 50 percent who didn’t, but that a placebo group obtained similar results. Moving on.

The American Pregnancy Association (APA) also suggests nipple stimulation to help induce labor. You can do this by using a breast pump or by just rubbing your nipples really, really hard. Doing so causes, again, the release of oxytocin and eventually contractions. (It’s the same concept as when baby breastfeeds right after birth, stimulating contractions and slowing the bleeding. Neat, huh?)

And what about getting busy?

"[My doctor] told me to have sex," Yakumin tells Romper. "I said, 'HOW?!' I was almost two weeks past my due date by then, and I was huge. She actually gave me a booklet with different positions to try, and lord help me, I took it home and told my husband, 'OK, we're doing this.'"

According to a 2001 study by UK's Royal College of Obstetricians and Gynecologists, the role of sex in inducing labor is unclear. They suspect a combination of physical stimulation and/or the hormonal makeup of sperm.

Says Artyomenko, "Sex can help at times because semen contains a prostaglandin that helps soften the cervix." Of course, this only works if your partner is male, because it's semen that's key. On the plus side, if you want to try this method, there's no better time to insist on the Big O — the oxytocin released by orgasm may also play a role. "You really want the semen in there, and then [you want to] stay in bed and let it sit on the cervix for awhile."

Doctors have also been known to recommend a dash of castor oil if you’re over 38 weeks along to help induce labor. The oil presses against the bowels, which in turn stimulates the uterus. But you better really, really want that baby out, because castor oil is also notorious for causing explosive diarrhea (and I'll stop there).

All of this may give the impression that you're supposed to go into full-on freakout, rush-to-the-doctor mode if your due date is ticking up and there’s no sign of anything changing.

But you shouldn't. At no time should you even try to induce labor before 41 weeks unless your healthcare provider gives you a good reason. "If you were having a high-risk pregnancy, some women might be concerned. [But] it is generally [typical] to go to at least 39 weeks, which is a term pregnancy, but more common to go 41 weeks," Artyomenko tells me. Plus, studies show many due dates are too early. Why risk forcing your baby out of her happy place before she’s ready?

In fact, talk to enough people about labor, and you hear one key word repeated: relaxation, which "is very important,” says Artyomenko, who also recommends exercise in the form of lunges — not to induce labor, but to coax the baby to descend. “In a healthy mom with a baby in a good position, labor will generally come," she tells Romper. So taking a warm bath and sipping a cup of jasmine tea may not induce labor per se, but it will help ensure you’re mentally prepared for it whenever it arrives.

Someone told me to drive over the speed bumps in the Toys R Us parking lot without slowing down.

For women likely to go into preterm labor, discovering the answer to the question is more important than mere curiosity. The UT Southwestern team found that these women often suffer from an infection of the membranes, which goes along with an increase in immune cells known as macrophages.

Usually, these macrophages are activated by the surfactant protein, but in preterm labor, bacteria binds to the receptor instead. By injecting a mouse with the protein, they've been able to control whether the mouse delivers late or early.

"If we knew more about this receptor on amniotic fluid macrophages, we may be able to design therapies or inhibitors to block preterm labor," Mendelson said in a press release.

As for Yakomin, she grew more desperate. "Someone told me to drive over the speed bumps in the Toys R Us parking lot without slowing down," she recalls.

In the end, two weeks late, she went to her doctor to get induced. "They started me on Pitocin, and also used prostaglandin gel at one point." She also got a membrane sweep, but eventually needed a C-section. As it turned out, she had a uterine defect that led to excessive bleeding. Even though she and the baby turned out fine, she calls it "a harrowing experience," and says she was thankful that none of the tricks worked.

"If I had gone into labor on my own, I might not have gotten to the hospital in time."

Although so much about labor is still a mystery, at the very least, scientific breakthroughs will someday ensure your baby can come out when she's ready — and not a moment too soon (or too late!).

Check out Romper's new video series, Bearing The Motherload, where disagreeing parents from different sides of an issue sit down with a mediator and talk about how to support (and not judge) each other’s parenting perspectives. New episodes air Mondays on Facebook.