Saliva test to identify women at risk of delivering early

Published on 07/22/09

An exploratory study to be published in BJOG, has shown that women going into early preterm labour (before 34 weeks gestation) have low-levels of progesterone in their saliva as early as 24 weeks, and that moreover, these levels fail to rise during pregnancy in the normal way. This offers the possibility of developing a simple, non-invasive test to identify women at increased risk of delivering early.

Progesterone is a hormone which helps regulate the menstrual cycle; but perhaps most importantly, it is the primary hormone of pregnancy. It is produced in large amounts from the placenta and acts to stop the womb from contracting.

Researchers at University College London and King’s College London, collected specimens of saliva from 92 women taking part in an existing randomised control trial (the PREMET study) of preventive treatment for preterm birth. Women recruited to the study all had an increased risk of having a preterm birth (they were selected based on having at least one risk factor such as a history of previous preterm birth, late miscarriage etc). Saliva samples were taken from these women every week from 24 weeks gestation until 34 weeks or delivery (whichever was the sooner), and analysed. Women were divided into three groups: delivery before 34 weeks, delivery between 34 – 37 weeks and delivery at term (after 37 weeks).

The results show that the concentration of progesterone in the saliva of women delivering after spontaneous labour before 34 weeks was significantly lower than those giving birth at term (after 37 weeks) at all gestational ages from 24 weeks onwards. The authors note that progesterone is known for its anti-inflammatory properties, and suggest that low levels of the hormone in the maternal body could contribute to bacterial infection, a recognised cause of early preterm labour. Based on their findings, researchers believe saliva progesterone could be a useful predictor of early preterm labour and delivery.

Lead author Professor Lucilla Poston, from the Maternal and Fetal Research Unit at King’s College London said, “This very interesting study, funded by Tommy’s, backs up previous research which hinted at the importance of low saliva progesterone as a marker for labour onset.

“We are now planning a much larger study to validate these preliminary findings. Saliva is easy to collect, there is no need for a needle or a blood sample and it would be wonderful if in the future we only had to ask a pregnant woman to produce a small sample of saliva to know whether or not she was at risk of very early premature birth.”

Jane Brewin, Tommy’s Chief Executive, added: “We are delighted with the results of this initial study. Backed by further research, we hope these findings will also have an impact on the development of preventative measures for preterm births.”

Professor Philip Steer, BJOG editor-in-chief, said “Despite advances in medicine, we are still a long way from understanding the causes of preterm birth in the human.

“This promising study, though small, suggests that salivary progesterone measurement could provide a useful early identification of women with an increased chance of an early premature birth. Further prospective research is needed on a larger cohort. Finding a reliable marker of impending preterm birth would allow us to try and develop targeted preventative measures.”

Lachelin G, McGarrigle H, Seed P, Briley A, Shennan A, Poston L. Low saliva progesterone concentrations are associated with spontaneous early preterm labour (before 34 weeks of gestation) in women at increased risk of preterm delivery. BJOG 2009; DOI: 10.1111/j.1471-0528.2009.


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