The purple line and its association with cervical dilatation in labour: A systematic review and meta-analysis

Abstract

Background: There is a growing body of evidence that the presence and length of the purple line could represent a non-invasive method of estimating and determining labour progress.

Objectives: The primary outcome was to provide a systematic review and meta-analysis on the association between the purple line length and cervical dilatation in active labour. The secondary outcome was to determine the association between the purple line length and the fetal head descent, and to calculate the pooled mean length of the purple line at a cervical dilatation of 3-4 cm and at a cervical dilatation of 9-10 cm.

Search strategy: We searched the Medline, Scopus, Cochrane Central Register of Controlled Trials (CENTRAL), Clinical Trials.gov and Cochrane Pregnancy and Childbirth's Trials Register databases from inception till March 25, 2023.

Selection criteria: We included observational studies of pregnant women in active first stage of labour who had their labour progress assessed with the use of regular vaginal examinations and who had the occurrence recorded and length of the purple line measured at the same time.

Data collection and analysis: Two reviewers independently evaluated study eligibility. We used the random effects and fixed effects model for meta-analysis.

Main results: There were six eligible studies included in the systematic review that reported on 982 women in total with the purple line appearing in 760 (77.3%) of cases. We found a moderate positive pooled correlation between the purple line length with cervical dilatation (r = +0.64; 95%CI: 0.41-0.87) and fetal head descent (r = +0.50; 95%CI: 0.32-0.68). For women either in spontaneous or induced labour, the pooled mean length of the purple line was more than 9.4 cm when the cervical dilatation was 9-10 cm, whereas it was more than 7.3 cm when the cervical dilatation was 3-4 cm.

Conclusions: The purple line is a non-invasive method that may potentially be used as an adjunct in labour progress assessment.

Keywords: Active labour; Cervical dilatation; Fetal head descent; Purple line; Vaginal examination.