Now we do a rectal examination

The OASI (Obstetric Anal Sphincter Injury) Care Bundle, endorsed by the Royal Colleges of both Obstetricians & Gynaecologists and Midwives (click here and here) recommends a digital rectal examination after every normal birth “even if the perineum appears intact”. The idea of such an intrusive procedure, at such a sensitive time, is to diagnose unrecognised external anal sphincter tears. But it makes no sense.

The external anal sphincter is a ring of muscle, about as thick as a finger, which maintains continence. If there is a perineal tear or episiotomy, the sphincter is usually exposed, and a trained midwife can either see a tear directly, or palpate it.  Such injuries affect 2-5% of vaginal births, and examining for them in the presence of a perineal tear is uncontentious, because immediate repair is recommended.

In contrast, in the absence of a visible injury, anal sphincter damage is rare. One group (click here) found no cases among 291 women examined later by endoanal ultrasound. (Seven percent had evidence of a “non intact” internal sphincter, but that is a thin layer of impalpable muscle fibres adjacent to the anal mucosa; no-one thinks you can diagnose damage to that that by rectal examination.)

Moreover, if the perineum is intact, palpation is an imprecise way to diagnose sphincter injury, because skin and the transverse perineal muscles lie in the way. Few midwives or doctors are trained to identify an anal sphincter tear when the perineum is intact.

And what is the midwife supposed to do if she diagnoses this rare injury in a woman with an intact perineum? Call a doctor to incise the skin and repair the damaged sphincter? I don’t think so! Thirty years ago, I’m told, an idiosyncratic consultant in Leeds, who believed in the existence of occult sphincter damage, occasionally did just that, but he was a poor role model, ending his career in disgrace following an unrelated conviction for sexually assaulting his patients.

Pelvic floor exercises are recommended anyway, and there’s no point in bringing women back for extra postnatal examinations, because no-one recommends late surgery in the absence of symptoms.

Routine rectal examination in the presence of an intact perineum fails all the criteria of a useful screening test. Most midwives wisely don’t do it. Those that do, should stop.

Jim Thornton