Two or three membrane sweeps are offered to overdue mothers in weeks 40 and 41 to start labour. Is it advisable to skip the first membrane sweep at week 40 and simply wait for a week, or does this decrease the probability of “spontaneous labour”, therefore leading to a higher chance of other means of induction?
Most of the literature I found looks at the efficacy of sweeps (vs. no sweep at all). They find that yes, sweeps are useful for bringing on labour.
But I did find an RCT that indicated that 40-week sweeps increased the effectiveness of 41-week sweeps:
one week later (at 39 weeks). However, nulliparous women had previously seemed to benefit most from sweeping of the membrane.
We think that weekly sweeping puts women in a pre-labour situation where irregular contractions have a cervical ripening effect. This may explain why our women assigned to sweeping of the membranes had a higher Bishop score on admission and a lower induction rate. Multiple sweeping may therefore be more effective that single sweeping.
This latter finding is in line with a recent randomised trial where women allocated to sweeping underwent a single sweep at 38 to 40 weeks of gestation and where no significant difference was found in the proportions of women who started labour spontaneously within seven days or before 41 weeks. However, a single sweep performed post-term was effective in promoting spontaneous labour. The timing of sweeping of the membranes may therefore be important. Future trials should aim at elucidating the optimum gestational age at which sweeping of the membranes should start.
So I think according to this study single sweeps before 41+0 are less effective than single sweeps after, but these authors seem to think that the pre-41 week sweeps may improve efficacy of the post-41 sweep. I'm curious if others draw the same conclusion.