Clinical Challenges at Caesarean Section : Uterine Rotation, Transverse Lie and Caesarean at Full Dilatation

Introduction

Caesarean section (CS) is a common operation of which the majority are straightforward. This risks a relaxed attitude to the procedure, and its occasional complexities can catch out the unwary. This chapter highlights important anatomical and surgical principles relevant to all CS but of particular importance in three challenging situations: an exaggerated or malrotated uterus, a transverse fetal lie, and in the second stage of labour. Many surgical difficulties can be avoided with forethought, and even if unavoidable, anticipating in advance enables mental rehearsal of strategies/techniques to overcome as well as early recognition of the problems when they are encountered.

Crucial Points of Uterine Anatomy at Cs

Development of the Lower Segment

In the nonpregnant state the uterus comprises body, isthmus and cervix. The serosal peritoneum over the body of the uterus is inseparable from the myometrium, whereas inferiorly the isthmus has a loose covering of peritoneum (the uterovesical fold) and the cervix lies directly behind the bladder ( Fig. 26.1 ). From the second trimester of pregnancy onwards the isthmus elongates and dilates to become the lower uterine segment and with advancing gestation the superior part of the cervix follows the same pattern. In normal circumstances the fully formed lower segment constitutes 70% isthmus and 30% cervix. Thus the point at which the free peritoneum fixes to the uterine serosa marks the upper limit of the lower segment of the uterus ( Fig. 26.1 ).

FIG. 26.1, Components of the uterus (a), their relationship with the peritoneal reflections (b) and their development during pregnancy (c). Note the upper limit of the lower segment is identified by the point at which the loose uterovesical peritoneal fold attaches to the myometrium. Above this level the serosa is inseparable from the myometrium.

The lower segment is therefore poorly developed at extremely preterm gestations, but can also be deficient when the fetal lie is transverse, with major placenta praevia and with isthmic fibroids.

Rotation of the Uterus

The distended sigmoid colon in pregnancy (exacerbated by the smooth muscle relaxing effect of progestogen) causes dextrorotation of the uterus, which can become exaggerated. Figure 26.2 shows a case where the uterus had rotated 180 degrees: in this extreme case there was no lower segment as the axis of rotation maintained the narrow isthmic and cervical pedicle inhibiting normal lower segment development.

FIG. 26.2, A uterus which rotated 180 degrees. In this case, it was not possible to correct the rotation before delivery and there was no identifiable lower segment, so a midline uterine incision was placed in the posterior aspect of the upper segment.

Fibroids can also have a huge impact on the position of the uterus as it grows: it is always worth checking an ultrasound scan performed very early in pregnancy to review the fibroid locations before the progressive uterine rotation due to pregnancy (and fibroid) enlargement. Late scans can be falsely reassuring that the fibroid lies laterally when it had arisen from the anterior isthmic wall: on entry, after correction of the rotation, it may inhibit access, and the opportunity to plan an appropriate incision might have been missed.

Changes in Labour

The myometrial fibres of the upper segment contract and shorten, pushing down on the fetus while pulling up on and stretching the lower segment. So, over time, the retraction of the upper segment causes it to shorten and get thicker while the lower segment gets thinner and ballooned. In normal circumstances this is accompanied by descent and then delivery of the fetus, but in advanced labour and especially when performing a CS at full dilatation the lower segment can be very ballooned out, extending high up towards the level of the umbilicus ( Fig. 26.3 ). This is most obvious in obstructed labour where a Bandl’s ring develops ( Figs. 26.3 and 26.4 ).

FIG. 26.3, (a) In normal labour the upper segment contracts and retracts and the lower segment is pulled over the descending presenting part of the fetus to effect cervical dilatation and delivery. (b) In obstructed labour the presenting part does not descend and the lower segment (which is still pulled up by the retracting upper segment) becomes increasingly elongated and ballooned out.

FIG. 26.4, Bandls ring. The constricting Bandls ring is situated at the junction of upper and lower uterine segments.

Surgical Precision at Cs

Checking and Correcting for Rotation

Safe precise technique at CS should be routine: checking symmetry of the broad ligaments/round ligaments prior to incising the uterus allows for correction of any rotation before incising the uterus. Failing to do this risks an asymmetrical incision, increasing the likelihood of a troublesome angle extension.

Identifying the Landmarks for the Junction Between Lower and Upper Segments of the Uterus

Appreciating that the loose peritoneum becomes fixed at the upper margin of the lower uterine segment:

Enables full assessment of whether there is an adequate lower segment available through which to allow access and delivery at very early gestations or when the fetus lies transversely.
Assists in positioning the uterine incision relatively high in the lower segment, thereby avoiding incising too inferiorly when it is ballooned out in advanced or obstructed labour.

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