Science Pinpoints When Your Labor Will Start

pregnant woman holding clock

The biggest guessing game for pregnant women—well, maybe besides whether it's a boy or a girl—is when Baby will decide to make an appearance. The onset of labor is a mysterious process, and due dates are not an exact science. In fact, only five percent of babies are born on their actual due date, according to one of two recent studies that are shedding light on new ways to better predict the birth day.

Using ultrasound to predict delivery

In the first study, published in BJOG: An International Journal of Obstetrics and Gynaecology, researchers examined whether measuring cervical length with a common and easy (if unpleasant) procedure, the transvaginal ultrasound, can predict when labor will begin. As delivery nears, the cervix shortens and dilates, or begins to open. In an analysis of data that included 735 women pregnant with one baby in the head-down position, the study found that when the cervix measured more than 30 millimeters at a woman's due date, she had a less than 50 percent chance of delivering within a week. But, if the cervix measured 10 millimeters or less, she had more than an 85 percent chance of delivering within a week.

Transvaginal ultrasounds have become the standard for assessing high-risk women's likelihood of preterm labor, so this research aimed to find out if the same is true for low-risk women at full term as well. Because of the positive results of the study, "we are hoping that these new transvaginal ultrasound cervical length checks would become routine, just once, at around 37 to 39 weeks," says senior author Vincenzo Berghella, M.D., director of Maternal Fetal Medicine at Thomas Jefferson University Hospital, and a professor of Obstetrics and Gynecology at the Sidney Kimmel Medical College at Thomas Jefferson University.

Whether or not the state of the cervix predicts full-term labor has been a debate for a while, especially when doctors use their own fingers to measure (called a "digital" check, not to be confused with the technology of an ultrasound). And OBs themselves differ in whether or not such checks are performed at the end of pregnancy. "There is no standard for routine digital cervical checks at present," Dr. Berghella says. With the results of this study, ultrasounds may be implemented more widely instead.

Although all these ultrasounds seem cost prohibitive, they actually might end up saving money by allowing hospitals and doctors to better plan for their patients' deliveries, and help women decide when to begin using their disability leave—in addition to relieving some of the anxiety of the guessing game. "There are several advantages, not only social, but also medical, like being able to better plan [whether or not to have] an induction of labor," Dr. Berghella says.

Having a cervical check at the end of pregnancy is a personal decision, but if you want one, Dr. Berghella says to ask your doctor about it in light of this new evidence. But why exactly is the onset of labor such a mystery to begin with? "Because we do not really know what starts labor well, and because of biologic variability among humans, plus external environmental factors, and different effects from different fetuses," he says.

So what actually causes labor?

A second study published in the journal PLOS One may help illuminate how the body knows when to start the delivery process. Researchers at The University of Texas Medical Branch discovered certain cell markers that happen as a woman starts labor. They found that changes in telomeres, part of our DNA that responds to aging, become present in the amniotic fluid as the placenta and other pregnancy tissues get older. These cells could be telling the baby that it's time to be born. "What made us suspect this signal is that we have always believed that labor can be triggered by the baby,"says  lead author Ramkumar Menon, Ph.D., an assistant professor in the department of Obstetrics and Gynecology, and co-author George R. Saade, M.D., a professor and chief of Obstetrics and Maternal Fetal Medicine. "We know that DNA from the baby and the placenta is released into the mother's blood all the time. So we assumed that if the baby is to send a signal to the mother that it is in trouble and needs to come out, the telomeres would be good candidates."

Because this natural aging process, or "senescense," happens all the time in our bodies, it's possible it could also be connected to the pre-labor changes in the cervix that transvaginal ultrasounds are detecting. "Senescence can affect any cells and organs. The same processes we found may also be occurring in the cervix," Menon and Dr. Saade say.

Unlike transvaginal cervix checks, though, more research is needed before telomere testing can be put into practice. "However, we have now shed light on a new mechanism by which the baby can signal to start labor," Menon and Dr. Saade say. "Knowing this mechanism will now allow us to develop clinical tests and treatments." It's just one more step toward unlocking the secrets of birth.


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