Ruptures to the anal sphincter during childbirth can cause long-term incontinence, pain and other problems for many women, so preventing them in the first place is key.
For the new study, researchers looked at whether anal tears could be prevented by a more traditional, "hands-on" approach to delivery - using a hand to slow the delivery of the baby's head, and telling the mother not to push during this stage.
Prior to 1980, this technique was commonly used in Norway, but fell out of favour. Then, starting in 2005, doctors at the Oestfold Trust Hospital in Eastern Norway began training in the traditional hands-on delivery technique.
Looking at more than 12 000 deliveries performed at the hospital between 2002 and 2007, researchers found that the rate of anal sphincter ruptures dropped from four percent in the years before the intervention, to just over one percent in the years afterwards.
Dr. Katariina Laine and colleagues report the findings in the journal Obstetrics & Gynaecology.
The "most dramatic" improvement, according to the researchers, was seen in the number of women with severe anal sphincter tears. Only one woman suffered a severe tear in the 18 months after the hospital's programme began.
Since the 1970s, Laine's team notes, hands-on assistance with the delivery of the baby's head has been thought of as relatively unimportant, and "so has been increasingly forgotten."
But the current findings, they say, show that the old-fashioned approach may spare many women a painful side effect of childbirth.