Could a new ultrasound measure predict mode of delivery?

By Eva Martin, MD of Elm Tree Medical, Inc.

We'd all love to be able to predict the future, especially when it comes to how a baby will be born: by vaginal, operative, or cesarean delivery. A cesarean delivery after labor is significantly more likely to lead to complications like hemorrhage or infection than a scheduled cesarean delivery. However, for the average low-risk woman, a spontaneous vaginal delivery is safer than any cesarean delivery. Obstructed (or stalled) labor is one of the largest contributors to our rising cesarean delivery rate. Therefore, predicting which women will ultimately need a cesarean delivery for obstructed labor could potentially lead to more effective care and possibly fewer complications. One approach to predicting mode of delivery is by analyzing the pelvic muscles as viewed through ultrasound.

In 2015, a group of researchers published data that women with a small "levator anterioposterior dimension" on ultrasound at 12 weeks gestation were more likely to have a cesarean delivery for failure to progress. In 2016, a group of researchers from Utrecht, Netherlands, decided to take a closer look at another ultrasound measure of the pelvic muscles: echogenicity. Echogenicity is how bright (black or white) an image appears on ultrasound. More black is a lower echogenicity and (for muscle tissue) means more muscle cells. More white is a higher echogenicity and indicates more extracellular matrix (collagen & fat). The authors theorized that echogenicity would provide insight into the functional and structural make-up of the puborectalis muscle, which could in turn predict mode of delivery.

The researchers gathered ultrasounds and medical records from 254 first-time moms who had participated in another study. The women had a mean age of 31, were normal weight on average, and completed two ultrasounds: the first at 13.3 weeks on average and the second at 36 weeks. The researchers measured the echogenicity of the puborectalis muscle using a computer algorithm from the images taken during the two ultrasounds when the muscle was at rest, when the women were holding their breath (Valsalva), and during a muscle contraction.

The results were mixed. The researchers found no association between mode of delivery and echogenicity for the first trimester ultrasounds when the muscle was at rest or during Valsalva. However, during a muscle contraction, women who ultimately had a cesarean section for failure to progress had a lower echogenicity (less extracellular matrix) than those who had a vaginal delivery, operative delivery, or cesarean delivery for non-reassuring fetal status. None of the measures at the 36 week ultrasound significantly predicted mode of delivery.

Why was the echogenicity only significant during a muscle contraction? The authors propose that the concentration of muscle cells in the ultrasound image increases during a contraction, allowing them to pick up on the slight differences in echogenicity between women. They also theorize that the 36 week ultrasounds were not predictive because of the normal increase in fat concentration in the pelvic muscles during pregnancy. In other words, the normal increase in muscle fat in all women obstructed the subtle differences between women. 

Did all women who eventually had a cesarean delivery for failure to progress have a low echogenicity in the first trimester? Nope. 75% did. As you might conclude, this test is not ready for prime time. The authors hope that new technologies using ultrasound to measure muscle strain and elasticity might one day combine with echogenicity to form a useful predictive tool. For now, however, they do not recommend integration of echogenicity into clinical care.

We want to hear from you! Do you think that ultrasound measures of the pelvic muscles will one day decide which women have scheduled cesareans and which attempt a vaginal delivery?