Research: different childbirth positions change pelvic position differently

But, as the researchers discovered, the biomechanics of labour (i.e. what happens to the body during labour and birth) have surprisingly not been studied much.

A team from the University of Lancashire (formerly the University of Central Lancashire) did a large review of scientific papers and found that there was not a single study that directly measured the biomechanics of labour. The review included 87 studies, and all of them focused only on pregnancy, not the birth process. The authors also note that most of the papers are observational, with small samples and poor representation of different groups: ethnicity was only specified in one paper.

Why it matters Biomechanical factors are associated with the risk of injury and complications for mother and baby. Unless doctors and midwives know exactly how postures and techniques change the position of the pelvis, spine and soft tissues, much childbirth care relies on tradition and assumptions rather than accurate data. Against the backdrop of the UK's discussion in recent years of rising maternal mortality and persistent differences by population group, the authors find this gap particularly worrying.

First step: they compared 7 "vertical" poses

To begin to close the gap, the researchers conducted a lab experiment: they compared seven common upright postures using two simultaneous motion capture technologies - marker-based(with cameras and body tags) and markerless. The study involved 15 healthy non-pregnant women (this is important: the work is not about actual labour, but about the basic mechanics of the poses).

The result: poses do vary greatly in body "geometry". For example:

• deep squat gave maximum hip flexion and extension,

• the B-Ball pose gave the greatest forward tilt of the pelvis,

• on all fours - the most pronounced pelvic tilt backwards,

• standing posture had the most flexion of the torso.

Comparison of the systems showed that the markerless technology in some places coincides with the "gold standard", but performs worse in some planes (especially in sagittal and body measurements), i.e. it still needs to be improved if it is to be used in the clinic.

The authors emphasise that this is not a clinical recommendation, but a "base" to move on to studies in pregnant women and, most importantly, to ethical ways of measuring biomechanics during actual birth, and in more diverse groups of women.