Only 5 percent of pregnant women deliver their baby on their due date; the rest are usually off by anything from days to several weeks. While this may not seem like a big deal, it can throw a mother’s schedule into chaos, especially if she works full-time and has to plan for maternity leave and care.

But new research published in BJOG: An International Journal of Obstetrics and Gynaecology describes a routine screening test that could help doctors estimate a more precise due date by measuring cervical length. Measuring cervical length is currently used to identify a woman’s risk of premature labor, as a shorter cervix typically means labor is likely to happen soon. The researchers hypothesized that the same measurement might also be able to predict birth at term too, so they gathered all the past studies (many with conflicting results) on the technique to get closer to a conclusion.

“Measuring cervical length via ultrasound at around 37-39 weeks can give us a better sense of whether a mother delivers soon or not,” Dr. Vincenzo Berghella, director of maternal fetal medicine at Thomas Jefferson University Hospital and lead author of the study, said in the press release.

Cervical length can provide information about labor due to the changes that occur in its size and softness. When the cervix begins to soften and change shape into a shorter cone, which would allow the baby to move toward the birth canal, a woman is likely to be entering labor soon.

Berghella and his team gathered data from five different studies that provided info on 735 women with single-child pregnancies. They found that when the cervix measured more than 30 millimeters on a mother’s due date, she had a lower than 50 percent chance of delivering within seven days. If the cervix measured 10 mm or less, however, her likelihood of delivering within seven days was much higher — at 85 percent.

More precise due dates could give women more leeway in planning for their pregnancy and childbirth — especially among busy mothers who work part- or full-time. Paid maternity leave (and even paternity leave) aren’t guaranteed for everyone, so it can often be a stressful, nerve-wracking time for mothers to adjust to a post-baby schedule. Knowing when labor will occur, and when to plan for maternity leave, could help reduce some of the stress and anxiety that comes with childbirth.

In addition, the months leading up to childbirth — and the following year — are essential to the health of both mother and child. Research shows time after time that having time to care for a baby after childbirth boosts both mother and child mental health, improves vaccination rates, lowers the infant mortality rate, and increases the amount of time for breastfeeding. Breastfeeding has been linked to numerous health benefits for both mother and child as well, such as a stronger immune system and improved cognitive function later in life for the infant.

“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,” Berghella said in the press release. “These are plans which help reduce a woman’s anxiety about the onset of labor. But having a better sense can also help obstetricians provide information that could help improve or even save a mother or baby’s life.”

Source: Saccone G, Simonetti B, Berghella V. Transvaginal ultrasound cervical length for prediction of spontaneous labour at term: a systematic review and meta-analysis. BJOG: An International Journal of Obstetrics and Gynaecology. 2015.