PROBLEM/BACKGROUND: Immersion in water has known benefits, such as reducing pain and shortening the duration of labour. The relationship between waterbirth and perineal injury remains unclear.

AIM: To compare the incidence of perineal injury in waterbirth and birth on land among low-risk women. Secondary outcomes were postpartum haemorrhage and 5-minute Apgar scores <7.

METHODS: Prospective cohort study of 2875 low-risk women who planned a home birth in Denmark, Iceland, Norway, and Sweden in 2008-2013 and had a spontaneous vaginal birth without intervention. Descriptive statistics and logistic regression were performed.

FINDINGS: A total of 942 women had a waterbirth, and 1933 gave birth on land. The groups differed in their various background variables. Multiparous women had moderately lower rates of intact perineum (59.3% vs. 63.9%) and primiparous women had lower rates of episiotomies (1.1% vs. 4.8%) in waterbirth than in birth on land. No statistically significant differences were detected in adjusted regression analysis on intact perineum in waterbirth (primiparous women's aOR = 1.03, CI 0.68-1.58; multiparous women's aOR = 0.84, CI 0.67-1.05). The rates of sphincter injuries (0.9% vs. 0.6%) were low in both groups. No significant differences were detected in secondary outcomes.

DISCUSSION: The decreased incidence of intact perineum among multiparous women was modest and inconclusive, and the prevalence of sphincter injury was low.

CONCLUSION: Low-risk women contemplating waterbirth should be advised to weigh the risks and benefits detected in this study against previously established benefits of waterbirth and should make an informed choice based on their values.