Letters

Vaginal delivery after caesarean section

Study's focus on induction v spontaneous labour neglects spontaneous delivery

Safety of single-layer suturing in caesarean sections must be proved

Study's focus on induction v spontaneous labour neglects spontaneous delivery

EDITORJosefson reports on a study by Lydon-Rochelle et al that found that induction of labour was associated with increased risk of uterine rupture.¹ Although the research isolated prostaglandins from other forms of induction, it failed to isolate those women induced specifically with oxytocic drugs and those who were not induced but were given augmentation. This more specific stratification could entirely change the risk levels and clinical implications for particular groups.

The study found that induction of labour without prostaglandins increased the relative risk significantly (to 4.9). As this cohort presumably included women who had induction by artificial rupture of the membranes, medicated forms of induction within this "other" category could pose an even higher relative risk.

Recent studies looking at augmentation have found it also to be associated with uterine rupture.^2-5 For example, Zelop et al found that induction with oxytocin was associated with a 4.6-fold increase in uterine rupture, and augmentation with a 2.3-fold increase.⁴ Because it is reasonable to assume that a good portion of the "inductions without prostaglandins" in the study reported by Josefson involved oxytocics, oxytocin induction and augmentation may be implicated.

By not clarifying which mothers were given augmentation the study lacks a clear cohort of mothers who had no intervention at all. Women who have had a previous caesarean section but neither induction nor augmentation could prove to be at lower risk of rupture than any of the groups isolated in the study. Isolating women who had no medicinal or mechanical stress could show that vaginal delivery for these women has a similar level of safety as the prescribed elective repeat caesarean.

Betty-Anne Daviss, chair. 
Statistics and Research Committee, Midwives Alliance of North America Midwifery Collective, Ottawa, Ontario, Canada K1S 2Z7 midwife{at}istar.ca

Safety of single-layer suturing in caesarean sections must be proved

EDITORJosefson reports that Lydon-Rochelle et al in Washington State found a tripling of the risk of uterine rupture with trial of labour compared with repeat caesarean section.¹ Similarly, about a doubling of the risk for trial of labour was reported for California in 1995 and in a recent evaluation in Switzerland.¹

These analyses, however, seem to be at odds with a meta-analysis of studies conducted in the United States in the 1980s comparing trial of labour with repeat caesarean section.² This meta-analysis did not find an increased risk of uterine rupture associated with trial of labour after caesarean section in the 11 studies (6328 births) examining the issue.

We propose that the risk differential in Washington, California, and Switzerland between repeat caesarean section and trial of labour is the result of a change in clinical practice in the late 1980s, when single-layer closure of the uterine incision during caesarean section became popular.³ An evaluation in Montreal covering 1990-2000 found a five-fold increase (odds ratio 5.2, 95% confidence interval 2.1 to 12.8) in uterine rupture associated with single-layer versus the traditional double-layer method.⁴ Among the 398 women with single-layer closure the rate of rupture was 3.3%, whereas among the 1251 women with double-layer closure it was 0.6% (P<0.001). Single-layer suturing could have a particularly large impact on the rate of uterine rupture among those women induced or given augmentation during labour.

Introduction of the single-layer method does not seem to have been based on evidence of safety or on evidence of not increasing uterine rupture in subsequent pregnancies. A Cochrane review of single-layer versus double-layer closure reported no studies examining relative safety in relation to uterine rupture in subsequent births.⁵

The increased risk associated with trial of labour observed by Lydon-Rochelle et al may well be the result of single-layer suturing during a previous caesarean. This would suggest that single-layer suturing should be abandoned until its safety with regard to uterine rupture in subsequent trials of labour can be established.

Kenneth C Johnson, consultant epidemiologist. 
Statistics and Research Committee, Midwives Alliance of North America, Ottawa, Ontario, Canada K1S 2Z7 Ken_LCDC_Johnson{at}HC-SC.GC.CA

Ina May Gaskin, president. 
Midwives Alliance of North America, 41 The Farm, Summertown, TN 38483, USA