Directing hip extension at crowning did not reduce tears

Design

Pragmatic, non-blinded randomised clinical trial

Population

1,206 nulliparous women with term singleton vaginal births

Primary outcome

Second- to fourth-degree perineal laceration

Effect

66.6% intervention vs 66.2% usual care (P=0.89)

A pragmatic US trial randomised nulliparous women at term with a singleton fetus to be directed, just before crowning, to lower their legs and extend their hips, or to usual care, where most delivered with hips flexed. The primary outcome was second-, third- or fourth-degree perineal tear.

Among 1,206 women who delivered vaginally, significant tears occurred in 66.6% with the intervention and 66.2% with usual care — no difference. A quarter of women allocated to extension did not adhere. In as-treated analyses, extension was linked to fewer anal sphincter injuries (5.2% vs 9.9%), but this did not hold after adjustment; an ordinal analysis suggested a small shift towards less severe tears.

The as-treated signal is hard to interpret, because women who could extend their hips may have differed from those who could not — a smaller baby or a slower final descent, for instance.

The practical message is negative but useful: telling women to change leg position at crowning is not a reliable way to protect the perineum. Effort is better spent on measures with stronger evidence, such as controlled delivery of the head and warm perineal compresses.

• Do not rely on directing hip extension at crowning to prevent perineal tears.
• Let women choose the position they find comfortable for the birth of the head.
• Keep using measures with better evidence, such as warm compresses and controlled delivery of the head.
• Examine every perineum systematically after birth, including a rectal examination, so sphincter injury is not missed.

Why it matters

It removes one plausible but unproven instruction from the second stage.

Don't overread it

The as-treated reduction in sphincter injury did not survive adjustment and may reflect who was able to adhere.

The statistics, in plain English

Intention to treat compares the groups as randomised and is the fair test; it showed 66.6% vs 66.2%. As-treated analysis compares what women actually did, which reintroduces the biases randomisation removed, so its unadjusted differences are weak evidence.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.