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Will you have a purple/brown/red line in your 'butt cleavage' during labor?

When couples in my classes are learning the Sacral Rub or sacral counterpressure, Double Hip Squeeze and Bladder32 accupressure techniques for coping in labor, I always talk about the great position the Partner is for spotting the ‘red, purple line or dark line’ (depending on skin color) that creeps up between the laboring woman’s buttocks and how – by ‘reading’ that line – he or she may know more accurately the woman’s cervical progress than the health care providers! This empowering thought is often met with smiles and laughter especially when I translate ‘natal cleft’ into more recognizable words like ‘butt cleavage’. Strangely, I’ve never had anyone in class mention having heard of this ‘thermometer’ for accessing cervical dilation by sight and I find this interesting considering the number of medical professionals that come through my classes.

I first came across this body of research as an Antenatal Student Teacher with the National Childbirth Trust in London. The article I was reading was in Practising Midwife and was a ‘look back’ at the original article (Hobbs L, 1998) published in the same magazine. The original Practising Midwife article was based on a letter referencing a small study by Byrne DL & Edmonds DK published in The Lancet in 1990.

In the 1990 letter to The Lancet, Byrne and Edmonds outlined and graphed 102 observations from eighteen midwifes on 48 laboring women. It states ‘The red line was seen on 91 (89%) occasions, and was completely absent in five (10.4%) women and initially absent in three (6.25%)’. The report then goes on to talk about the ‘significant correlation between the station of the fetal head and the red line length’. Later the authors write: ‘To our knowledge, this is the first report of this red line. We believe that it represents a clinical sign which is easy to recognize and which may offer valuable information in obstetric management’.

So how does this line work? And why does this it appear? Practising Midwife Magazine presented a graphic which I have attempted to recreate here. Basically as the baby descends, a red/purplish (or perhaps brown depending on skin color) line creeps up from the anus to the top of the natal cleft in between the bottom cheeks:

Complete 10cm dilation would mean the line has reached the top of the natal cleft. Most of the time the woman would need to be bent forward to see the line.

When the line reaches the top of the natal cleft, 2nd stage is probably a matter of minutes away. A line sitting an inch below the natal cleft is probably in transition. A line just above the anus probably signifies early labor. Byrne DL & Edmonds DK, the authors of the original study, surmise that the cause of the line is ‘vasocongestion at the base of the sacrum’. Furthermore, the authors reason that ‘This congestion possibly occurs because of increasing intrapelvic pressure as the fetal head descends, which would account for the correlation between station of the fetal head and red line length’. Fascinating and logical!

Interestingly, I came across a 2nd (Scottish) study from 2010 published by BMC Pregnancy & Childbirth:, [SM6] (Shepherd A, Cheyne H, Kennedy S, McIntosh C, Styles M & Niven C) which aimed to assess the percentage of women in which a line appeared (76%. ) The study cited only 48-56% accuracy of vaginal examinations to determine cervix diameter and fetal station. So why aren’t clinicians using this less invasive visual measure – especially considering how much most women dread vaginal exams in labor? Wouldn’t the thought of using a methodology to lower infection rate after ROM enthuse Care Providers instead of using higher risk techniques? Or how about using the accuracy of the line at the natal cleft to know when a women using epidural should really be coached to push?

My educated guess is that this information has not yet reached Medical Textbooks and non-standard practices can take years to become mainstream (ie. delayed cord clamping) – and then only if or when women request them or media sensation activates them. In addition, since laboring women are only intermittently attended by Labor & Delivery staff during early and active labor and often encouraged to ‘stay on the bed’, Health Care Providers aren’t necessarily faced with a woman’s buttocks in labor. Also vaginal examinations are considered ‘accurate’ so staff have no need to peek between a women’s natal cleft. However both these studies, paired with the roughly 50% accuracy rate of manual vaginal exams, show that there is potentially a more accurate and less invasive way ahead.

In The Practising Midwife (Jan 2007, Vol 10 no 1, pg 27), Lesley Hobb’s writes “Accurate reading would seem to the key to this practice. I sometimes notice in myself a wish to see the line progressing more quickly than it actually does; when I do this – and check with a VE – only to find the line is right, I get annoyed with myself and wish I’d trusted my observations”. Later she goes on to say “I can now envisage a time when I shall feel confident enough to use this as my formal measurement mechanism and abandon intrusive and superfluous vaginal exams”.

Licensed Midwife Karen Baker from Yucaipa, CA commented “The purple line is a curious thing. It’s definitely not present on everybody but is more prominent on some than others – especially right before pushing. It tells us when she’s in full swing if we are in a good position to spot it!”

I often urge couples to send me a picture of the so called ‘purple line’ which I promise I will use only for educational purposes (!) but so far a picture is as elusive as the Loch Ness Monster. So, as I say in class, ‘show me your purple line’! Have you heard of it or witnessed it?

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