What causes preterm labour?

Learn the risk factors that make you more likely to deliver a baby before 37 weeks of pregnancy.

When she was 30 weeks pregnant, Natalie Séguin-Brilliant woke up with excruciating cramping and pain, and her midwife told her to head to the hospital right away. While some cramping during pregnancy can be normal, Séguin-Brilliant was pregnant with twins, which means she was high-risk—and preterm labour was a definite possibility.

It turns out, one of her babies had its foot on her cervix, and she was already one centimetre dilated. By the time she was transferred to a hospital specializing in high-risk pregnancies, she was three centimetres dilated. Her baby girls were born shortly afterward by emergency C-section.

Almost eight percent of babies in Canada are born before 37 weeks, the point when they are considered full-term. Being pregnant with twins is just one of the risk factors of preterm delivery. Here’s a look at some of the common causes of having your baby earlier than expected.

1. Carrying multiples

When you’ve got more than one baby in your uterus, it behaves as though the pregnancy is further along than it actually is. “It’s being stretched to a certain capacity, which can bring on the preterm labour contractions that lead into true labour,” says Christy Pylypjuk, a specialist in maternal-fetal medicine at the Health Sciences Centre in Winnipeg. She adds that the extra stretching can increase the chance that the rupture of membranes will happen early as well. Carrying multiples also increases your chances of having problems with the placenta or developing conditions like hypertension or diabetes during pregnancy, which can all increase the possibility your care provider will want to deliver the babies early, for your health or your babies’. Because babies conceived by IVF are often multiples, IVF is also considered a risk factor for preterm delivery.

2. Dealing with extremes of age

Both very young mothers and mothers over the age of 35 have a greater chance of delivering babies early. Teenage moms often have lower socio-economic backgrounds and may have poor nutrition or irregular prenatal care. When it comes to older moms, “you’re actually at a higher risk of almost everything in pregnancy,” says Amanda Selk, an ob-gyn at Women’s College Hospital in Toronto. Older women are more likely to have or develop conditions like high blood pressure and diabetes when they get pregnant. But that doesn’t mean all older moms will have a high chance of a preterm delivery. “There’s a lot of evidence to show that if you are a very healthy mom, who perhaps is over the age of 35 or 40, many of these women can have an absolutely uneventful, straightforward pregnancy,” says Pylypjuk.

3. Medical complications

There are many complications that come up during pregnancy that could lead to preterm labour or cause your health-care provider to induce labour or perform a C-section. Placenta previa (where the placenta partially or totally covers the cervix), placental abruption (where the placenta spontaneously separates from the uterine wall before labour), an incompetent cervix, gestational diabetes, bladder infections and pre-eclampsia (a pregnancy complication that involves high blood pressure and can be dangerous for the mom and baby) are just a few examples. Early and regular prenatal care will help identify and manage these conditions to reduce the chances of an early delivery.

4. Sleep disorders

If you’ve been diagnosed with insomnia, sleep apnea or another sleep disorder, you may be at an increased risk of having a preterm birth. A study from the University of California San Francisco found that women with sleep apnea and insomnia were about twice as likely to have their babies before 34 weeks as those who did not have a sleep disorder. Some sleep changes during pregnancy are normal, but if you have more serious ongoing sleep issues, talk to your doctor because sleep disorders can be treated.

5. Sleep disorders

Getting into a car accident or falling on an icy sidewalk is unlikely to kick-start contractions, but it can disrupt the placenta. “This increases the chance of things like placental abruption, impaired blood flow to the baby and hemorrhages, which can lead to an indicated preterm delivery because of maternal or fetal distress,” says Pylypjuk. If you experience an accident or fall, you should head to the triage department at the hospital, where a care provider will monitor you for up to four hours.

5. Prior history

If you’ve had a preterm birth already, you are at a much higher chance of doing so again. “If you have a positive pregnancy test and a history of preterm birth, you should present to your health-care provider as soon as possible,” says Pylypjuk. In many cases, you would be advised to follow up with your care provider even before getting pregnant again. “If we can figure out what the specific risks or causes were in that pregnancy, we can try to do everything we can in the next pregnancy to prevent it,” says Selk. For example, depending on what the cause was, your doctor might recommend progesterone, which reduces the chance of preterm labour due to a shortened cervix, or, if hypertension is an issue, a low dose of aspirin early in pregnancy. (These are not recommendations they would suggest for all women, but interventions that might make sense if you’ve had a previous preterm delivery.)

Can I prevent a preterm labour?

Despite knowing the risk factors for preterm birth, the experts say there’s not a lot you can do to prevent it. “The best strategy is to become aware of all of the risk factors and address the ones that are within your control, such as cultivating a healthy pre-pregnancy weight, quitting smoking, seeking prenatal care early and attending visits as scheduled,” says Alix Bacon, president of the Midwives Association of B.C. She points to the fact that the preterm birth rate in Canada has remained pretty constant from 2000 to 2013. But, says Selk, “There is no evidence that things like sex or exercise cause preterm labour.” And although it might seem like bedrest would be a good precaution against early labour, the utility of bedrest is being questioned by doctors more and more. “There is no evidence that putting people on bedrest helps,” says Selk. Pylypjuk agrees, “We really do encourage women to remain active during pregnancy,” she says. For a woman with a short cervix, a care provider might recommend limiting the amount of heavy lifting or straining she does, but that doesn’t mean being sedentary.

Séguin-Brilliant didn’t feel ready to welcome her babies so soon, but she’d been told by her midwives that preterm labour was a possibility anytime after 27 weeks. After a five-week stay in the NICU, Séguin-Brilliant’s twins—Kiera and Ava—came home. Now, at four and a half months old, they are healthy and thriving.

Read more:
Study: Avoiding these three things can help you prevent preterm labour
What you should know if you have a preterm baby
Life in the NICU: A case study in hope

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