Extending the hips at crowning did not prevent perineal tears

Design

Pragmatic, randomised, unblinded clinical trial

Population

1,206 nulliparous women with singleton term pregnancies who birthed vaginally

Primary outcome

Second-, third- or fourth-degree perineal laceration

Effect

66.6% with hip extension vs 66.2% usual care (P=.89, intention to treat)

A pragmatic, unblinded randomised trial in Obstetrics and Gynecology (22 September 2026) asked whether nulliparous women told to lower their legs and extend their hips just before crowning would tear less than those left in the usual flexed position. 1,206 women with singleton term pregnancies delivered vaginally after randomisation.

On intention to treat, second-degree or worse tears were no less common: 66.6% with the instruction and 66.2% with usual care. A quarter of women allocated to extension did not adopt it. When women were analysed by the position they actually delivered in, extension looked better for both significant tears (62.7% vs 68.7%) and sphincter injury (5.2% vs 9.9%), but those differences lost significance after adjustment. An ordinal analysis showed a modest shift towards intact perinea in the extension group.

The primary answer is no. The as-treated signal is the kind that tempts, but women who could straighten their legs at crowning may simply have been having easier births. There is no reason to make hip extension a routine instruction on this evidence, and no reason to stop a woman who finds it comfortable.

• Do not add a routine instruction to straighten the legs at crowning to prevent tears.
• Let women choose the birth position they find comfortable; this trial found no harm from extension.
• Keep using the perineal protection measures your unit already relies on, such as controlled delivery of the head.
• Expect about two in three first vaginal births to involve a second-degree or worse tear, as in this trial.

Why it matters

It removes a cheap-sounding fix from the list, and shows how an as-treated analysis can flatter a null trial.

Don't overread it

The lower sphincter injury rate appeared only in the unadjusted as-treated analysis and is not evidence of benefit.

The statistics, in plain English

Intention to treat compares women as randomised, which protects against the bias of who could comply. Here it showed no difference. As-treated analysis compares women by what they actually did, which reintroduces that bias; when the researchers adjusted for differences between groups, the apparent benefit was no longer statistically significant.

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