This Routine Screening Test May Better Predict Your Due Date

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By Anisa Arsenault, Associate Editor
Updated March 2, 2017
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Some moms are robbed of a baby shower thanks to their preemies. Others go to town on spicy food at 41 weeks in the hopes of finally inducing labor. While they sit at opposite ends of the spectrum, the takeaway is the same: Due dates are not set in stone.

This is not news, of course. But what if there were a way to predict that due date with more accuracy? Still, bodies handle pregnancy differently. And researchers think your cervix might be able to indicate that.

“Measuring cervical length via ultrasound at around 37 to 39 weeks can give us a better sense of whether a mother deliver soon or not,” says Vincenzo Berghella, MD, senior author of a new study published in BJOG: An International Journal of Obstetrics and Gynaecology (BJOG).

Typically, cervical length has been a predictor of premature labor; the shorter the cervix, the more likely labor is close. This study marks the first time researchers have investigated whether cervical length could help predict term births.

To conduct their analysis, researchers looked at various studies involving 735 women with singleton pregnancies whose babies were in the proper head-down position. When the cervix was 30 millimeters at a woman’s due date, her chance of giving birth within seven days was less than 50 percent. But when it measured 10 millimeters or shorter, their chances of delivery within seven days increased to over 85 percent.

Wondering why cervical position is so indicative of labor? After preventing your fetus from descending down the birth canal for nine months, the cervix starts to soften as your body prepares for labor. It shortens as the top flattens against the curve of your uterus. When this process starts too early, it initiates preterm labor. Noting cervical shortness early on could allow for doctors to intervene, delaying preterm birth with medication.

“Women always ask for a better sense of their delivery date in order to help them prepare for work leave, or to make contingency plans for sibling-care during labor. These are plans which help reduce a woman’s anxiety about the onset of labor,” says Dr. Berghella. “But having a better sense can also help obstetricians provide information that could help improve or even save a mother or baby’s life.”

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