Dystocia is difficulty in labour. There may be problems with the passenger (large baby, see impacted shoulders = shoulder dystocia p 72, or an abnormal presentation), the passages (for ideal pelvis, see p 42 note that cervical dystocia may be a problem after biopsy of the cervix, or a consequence of female genital mutilation p 246) or of propulsion (the uterine powers). Cephalopelvic disproportion results if diameters are unfavourable (p 42).
The pelvis
The ideal pelvis has a round brim (ie gynaecoid), but 15% of women have a long oval brim (anthropoid). A very flat brim is less favourable (platypoid); occurring in 5% of women over 152cm (5ft), it occurs in 30% of women <152cm. Spinal scoliosis, kyphosis, sacralization of the L5 vertebra, spondylolisthesis and pelvic fractures may all affect pelvic anatomy. Rickets and polio were formerly important causes of pelvic problems. Suspect pelvic contraction if the head is not engaged by 37 weeks in a Caucasian primip (after excluding placenta praevia).
The presentation
Cephalic presentations are less favourable, the less flexed the head. Transverse lie and brow presentations will always need caesarean section: face and OP (p 71) presentations may deliver vaginally but are more likely to fail to progress. Breech presentation is particularly unfavourable if the fetus >3.5kg.
The uterine powers
Contractions start in the fundus and propagate downwards. The intensity and duration of contractions are greatest at the fundus, but the contraction reaches its peak in all parts of the uterus simultaneously. Normal contractions occur at a rate of 3 per 10min, they should last up to 75sec, the contraction peak usually measures 30“60mmHg, and the resting uterine tone between them should be 10“15mmHg. Uterine muscle has the property of retraction. The shortening of the muscle fibres encourages cervical dilatation.
Uterine dysfunction
Contractions may be hypotonic (low resting tone, low contraction peaks) or they may be normotonic but occur too infrequently. These dysfunctions can be corrected by augmentation with oxytocin (p 64). Whenever oxytocin is used discuss with a senior obstetrician. Pain and fear cause release of catecholamines which can inhibit uterine activity. Thus adequate analgesia is needed (p 66) and may speed the progress of labour.
Cervical dystocia
Failure of cervical dilatation may be due to previous trauma, repair, cone biopsy, and cauterization. It is difficult to distinguish from failure to dilate due to uterine dysfunction though the latter should respond to oxytocin (note the important difference between primips and multips, p 64). The treatment for cervical dystocia is delivery by caesarean section.
Consequences of prolonged labour
Neonatal mortality rises with prolonged labour as does maternal morbidity (especially infection). With modern management of labour, careful monitoring of progress in labour (p 64) takes place to diagnose delay early, and treat it as necessary, to prevent prolonged labour occurring.
When there is dystocia, ask ˜is safe vaginal delivery possible?
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