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Open Access Highly Accessed Research article

The purple line as a measure of labour progress: a longitudinal study

Ashley Shepherd1*, Helen Cheyne2, Susan Kennedy3, Colette McIntosh1, Maggie Styles1 and Catherine Niven2

Author affiliations

1 Department of Nursing and Midwifery, University of Stirling, Stirling, FK9 4LA, UK

2 Nursing, Midwifery and Allied Health Professions Research Unit, University of Stirling, Stirling, UK

3 Forth Valley NHS Trust, Stirling Royal Infirmary, Stirling, FK8 2AU, UK

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Citation and License

BMC Pregnancy and Childbirth 2010, 10:54  doi:10.1186/1471-2393-10-54

Published: 16 September 2010

Abstract

Background

Vaginal examination (VE) and assessment of the cervix is currently considered to be the gold standard for assessment of labour progress. It is however inherently imprecise with studies indicating an overall accuracy for determining the diameter of the cervix at between 48-56%. Furthermore, VEs can be unpleasant, intrusive and embarrassing for women, and are associated with the risk of introducing infection. In light of increasing concern world wide about the use of routine interventions in labour it may be time to consider alternative, less intrusive means of assessing progress in labour. The presence of a purple line during labour, seen to rise from the anal margin and extend between the buttocks as labour progresses has been reported. The study described in this paper aimed to assess in what percentage of women in labour a purple line was present, clear and measurable and to determine if any relationship existed between the length of the purple line and cervical dilatation and/or station of the fetal head.

Methods

This longitudinal study observed 144 women either in spontaneous labour (n = 112) or for induction of labour (n = 32) from admission through to final VE. Women were examined in the lateral position and midwives recorded the presence or absence of the line throughout labour immediately before each VE. Where present, the length of the line was measured using a disposable tape measure. Within subjects correlation, chi-squared test for independence, and independent samples t-test were used to analyse the data.

Results

The purple line was seen at some point in labour for 109 women (76%). There was a medium positive correlation between length of the purple line and cervical dilatation (r = +0.36, n = 66, P = 0.0001) and station of the fetal head (r = +0.42, n = 56, P < 0.0001).

Conclusions

The purple line does exist and there is a medium positive correlation between its length and both cervical dilatation and station of the fetal head. Where the line is present, it may provide a useful guide for clinicians of labour progress along side other measures. Further research is required to assess whether measurement of the line is acceptable to women in labour and also clinicians.