Discussion
Main findings
In this study, the analysis of pelvic floor sEMG data at 6-8 weeks
postpartum in primiparous women represented that the fast muscle
strength was significantly weaker in VD compared with CD, as well as for
the slow muscle, muscle strength and stability of contractile control
were both significantly weaker in VD compared with
CD. The vitality of the pelvic
floor muscles decreases significantly after pregnancy, and the
supporting force becomes weaker. The high pressure generated by
pregnancy and delivery to the pelvic floor results in the impairment of
PFM, connective tissue and nerves, eventually leading to PFD. Numerous
previous studies have shown that compared with cesarean section, the
incidence of PFD, like pelvic organ prolapse (POP), stress urinary
incontinence (SUI) and so on in women with vaginal delivery is
significantly higher [10-12]. Blomquist[13] found that the cumulative incidence of POP,
SUI and overactive bladder (OB) after vaginal delivery was associated
with decreased PFM strength. A meta-analysis [14],
reviewed in total nine studies, also demonstrated the PFM strength in
the VD group was significantly lower than that in the CD group. Our
study aligned with other reports, suggested that vaginal delivery, as
the main risk factors for impairment of postpartum PFM strength, can
affect postpartum PFM function via decreasing the muscle strength of the
fast and slow muscles and the stability of the slow muscles.
Several studies[14,15] suggest that elective cesarean delivery
may protect the pelvic floor muscles. But other reports[16] showed that this protection from cesarean
delivery could be ignored with the long-term postpartum follow-up and
its effects in this regard remain controversial. Our study found that
the mean values of the pre-baseline and post-baseline rest in sEMG were
higher at early postpartum of the CD group than those in the VD group.
Guo et al [17] found the higher pressure at
pre-baseline rest in CD in the early postpartum compared with VD group,
which is consistent with our findings. The pre-baseline and
post-baseline resting phases is correlated to
the magnitude of muscle tension in a
relaxed state. Increased resting tension of pelvic floor muscles can
easily lead to pelvic floor muscle ischemia, present as clinical
symptoms such as dyspareunia, urinary retention, and constipation. A
study on quality of life with 6 years follow up postpartum[18], revealed that the incidence of lower
abdominal, genital pain, and pain related to sexual life were
significantly more frequent after cesarean delivery than that with
vaginal deliveries. The causes of increased muscle tone could be
neurogenic and non-neurogenic hypertonicity, which are both associated
with muscle contraction and/or passive stiffness[19]. Our findings suggest that cesarean section
may increase pelvic floor muscle tension and impact the PFM function in
the early postpartum period. The relevant mechanism needs further
investigation.
Numerous studies have shown that
assisted vaginal delivery, especially forceps delivery, significantly
increases the risk of PFD. The study
reported that the risk of fecal incontinence and POP was significantly
higher in those had assisted vaginal delivery
compared with natural vaginal
delivery [20]. Meyer et al[21] reported a higher incidence of PFM weakness
(20% vs 6%) in women with forceps delivery than spontaneous delivery
at 10 months postpartum. Among all kinds of vaginal deliveries, forceps
delivery brings the highest risk of impairment of pelvic floor
structure, mainly due to its potential destruction on the pelvic floor
muscles, nerves, and connective tissue. Weakened PFM strength may be
caused by levator avulsion injuries and extensive levator hiatus[22]. Our results suggest that the forceps
delivery has the worst impact on the PFM function among all vaginal
delivery in the early postpartum period, mainly by reducing the muscle
strength of fast and slow muscles as well as the stability of slow
muscles. And for those with necessary forceps delivery as high-risk PFD
population, pelvic floor function assessment should be performed at the
early postpartum stage, and a precise and effective strategy for
postpartum PFM recovery should be initiated as early as possible.
So far there are no reports on comparison of abdominal muscle engagement
among the different modes of delivery. In our clinical routine, EMG
signal representing the abdominal muscle engagement, was captured by an
additional channel via the patch attaching the abdomen. Our results
showed that the engagement of the abdominal muscles was significantly
higher in VD compared with CD. The potential reason behind could be the
compensative utilization of abdominal muscle in vaginal delivery group
as they had weakened pelvic floor muscle. The discordance of
pelvic-abdominal muscle was more pronounced in women who delivered
vaginally, thus their pelvic floor muscle requires the professional
rehabilitation therapy.