The Bottom Line: An Alternative Method for Checking Cervical Dilation

The standard method for birth professionals to measure cervical dilation and effacement is the vaginal examination.  When a midwife or doctor checks a woman’s cervix, she reaches her gloved hand inside the vagina and measures how many finger widths the opening of the cervix is.  A centimeter is approximately the same size as a finger tip so she can tell how how dilated a woman is by how many finger tips her cervix measures.  This method of checking for cervical dilation, however, is not always accurate.  According to a study published by BioMed Central, the accuracy of vaginal examinations for determining dilation is only 48-56 percent accurate.  Moreover, vaginal exams may introduce bacteria into the cervix and can be uncomfortable for some women during labor. 

The purple line

There are other methods for checking cervical dilation.  One method measures the length of a purple line that appears along a laboring woman’s natal cleft (or the crease/crack of her butt) when she is about 2 centimeters dilated.  Measuring this line, called the purple line or the bottom line, is a non-invasive way for caregivers to assess cervical dilation.  By measuring the length of this purple line and comparing it with the total length of a woman’s natal cleft (or the entire length of the crease of her butt), a midwife can determine approximately how dilated a woman is.  When the line grows to the top of the natal cleft, she is fully dilated.

What causes the purple line?

Researchers believe that the purple line is a result of vasocongestion in the sacrum.  As the baby descends into the birth canal, he puts more pressure on the pelvis and the sacral veins, causing swelling to occur which results in the appearance of a purple line.

Research on the bottom line

There has been very little research on the “purple line.”  The first documented study on the appearance of a purple line during labor was published in 1990 in the medical journal The Lancet.  Researchers Dominic Bryne and DK Edmonds looked at 48 women in spontaneous labor.  They found that a red line was present in 89 percent of the women, 10 percent of the women did not have a line at all, and the remaining 6 percent of the women did not show a line at first, but later did.  Another study published by BioMed Central found that 76 percent of the women studied had a purple line present at some point during their labor.

The research on “the bottom line” is intriguing.  Because of the limited data on its use during labor, finding a midwife or doctor that uses this technique may be difficult.  Based on the research, not every woman develops this line during labor.  However, for the women that do, this appears to be a promising new tool for measuring progress during labor. 

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