LONDON - British fertility researchers have developed an accurate way to predict which pregnancies are most likely to miscarry and say it could help doctors target treatment at women who really need it.

In a study presented at European Society for Human Reproduction and Embryology conference in Stockholm, researchers found six factors with the greatest impact on miscarriage risk -- a history of subfertility, levels of progesterone and of the pregnancy hormone human chorionic gonadotrophin (hCG), foetus length, the extent of bleeding, and the baby's gestational age.

Individually, these factors were unable to predict accurately the risk of miscarriage, but when the researchers combined two of them -- bleeding and hCG levels -- to create a "Pregnancy Viability Index" (PVI), they found this was a consistently reliable predictor of miscarriage.

"This research has, for the first time, offered us a robust tool to begin to attempt to rescue pregnancies threatening to miscarry when currently all we can do is fold our hands and hope for the best," said Kaltum Adam of Britain's St Mary's Hospital in Manchester, who led the study.

Around 20 percent of all pregnancies threaten to miscarry and about up to 20 percent of those do. Until now, doctors had no way to predict which threatened miscarriages would result in the end of the pregnancy and so could not target rescue attempts at the right women or offer them counselling.

In Britain, around 250,000 miscarriages occur every year, causing significant psychological distress to affected women and their families.

"This has led to wasteful and potentially harmful interventions, including unnecessary blood tests, ultrasound scans, hospital admissions for bed rest, sexual abstinence, low dose aspirin and progesterone supplementation," Adam said.

Between 2009 and 2010, Adam's team followed 112 women with threatened miscarriages who were between six and 10 weeks pregnant. During the five weeks of the study the women had ultrasound scans, weekly charting of pain and bleeding and weekly tests to check the levels of progesterone and hCG.

After analysing data on the outcomes of these pregnancies, Adam found there were six most important miscarriage factors, and from there the researchers developed their PVI scale.

"The PVI was able to accurately predict the pregnancy outcome in 94 percent of women who had ongoing pregnancies, and also predicted the outcome in 77 percent of women whose pregnancy ended in miscarriage," Adam said in a statement.

She said the PVI could now enable doctors to avoid unnecessary treatment in around 80 percent of women with threatened miscarriage, who currently often have repeated blood tests and ultrasound scans to monitor the pregnancy.  

"The use of the PVI will negate these in the vast majority of these women, as we will be able to reassure them of a high likelihood of pregnancy continuation and that there is little additional value in doing further testing," Adam said.

She said the PVI would also allow doctors to focus on the remaining 20 percent of risky pregnancies that do go on to miscarry, hopefully giving them a better understanding of the what goes wrong and how they might be rescued.