- Design
- Retrospective matched cohort, North Denmark Region, 2019–2024
- Population
- 277 births to women with vulvar lichen sclerosus and 533 control births
- Primary outcome
- Perineal tears, including obstetric anal sphincter injury
- Effect
- Second-degree tear RR 1.37 (95% CI 1.14–1.65); sphincter injury RR 3.37 (1.30–8.76)
A Danish regional cohort compared 277 births to women with diagnosed vulvar lichen sclerosus with 533 births to unaffected women, taking the next two births in the region as controls for each case. After adjusting for parity, birth weight, head circumference and vacuum delivery, lichen sclerosus was associated with more second-degree tears and with more than three times the risk of obstetric anal sphincter injury.
Within the lichen sclerosus group, sphincter injury clustered in nulliparous women, vacuum births, women with a narrowed introitus and women who had vulvar symptoms during pregnancy. Those last two are things a clinician can see or ask about before labour.
The absolute numbers are small and the confidence interval for sphincter injury is wide, so the size of the risk is uncertain. But the direction is plausible: the disease scars and stiffens the tissue the head has to stretch. Lichen sclerosus is also under-diagnosed, so many affected women will reach labour without anyone knowing.
In practice, ask about vulvar itch and soreness at booking, examine when symptoms are present, and record the diagnosis where the intrapartum team will see it. Active disease in pregnancy can be treated with topical steroids, as it would be outside pregnancy.
- Ask about vulvar itch, soreness or pain with intercourse at the booking visit.
- Record a known lichen sclerosus diagnosis on the labour plan so the delivery team sees it.
- Note introital narrowing on examination; it marked the highest sphincter-injury risk in this cohort.
- Consider these women higher risk for anal sphincter injury when planning an assisted vaginal birth.
- Examine the perineum and anal sphincter carefully after delivery in women with the condition.
Why it matters
A vulvar skin disease that is often missed in young women may be shaping perineal outcomes no one has planned for.
Don't overread it
This was observational with few sphincter injuries; it does not show that treating the skin disease prevents tears.
The statistics, in plain English
A relative risk of 1.37 means second-degree tears were about a third more common. The sphincter-injury estimate of 3.37 has a confidence interval from 1.30 to 8.76: the risk is probably raised, but it could be modestly or greatly raised. The risk factors within the lichen sclerosus group come from unadjusted comparisons in a small number of injuries, so they are weaker than the headline.
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