A total of 4511 participants were excluded, and 21302 participants were included in this analysis. The mean age, height, weight, body mass index (BMI), gestational weight gain (GWG), and neonatal weight (NW) was 30.43 ± 4.035 years, 160.37 ± 5.240 centimeters, 59.78 ± 8.084 kilograms, 23.23 ± 2.834, 12.88 ± 4.651 kilograms, 3.27 ± 0.516 kilograms respectively. There were 13211 patients with one parity, 7348 with two, 698 with three, and 45 with more than three. 18.0% received less than 12 years of education, 82.0% received more than 12 years. 94.3% of the infants weighed less than 4 kilograms, 5.7% more than 4 kilograms. 97.9% was single births and 2.1% was twin or triple births. 36.0% had cesarean section (CS), 49.2% had non-instrumental vaginal delivery (NIVD), 12.2% had episiotomy (EP), and 2.6% had forceps delivery (FD). Baseline demographic features are summarized in Table 1.
Table 1
General characteristics of research participants
Variables | Group | Number (%) | Mean ± SD (median) |
Age | ≤ 29 | 9066(42.6) | 30.43 ± 4.035 |
| 30–39 | 11809(55.4) | |
| 40–49 | 427(2.0) | |
Height | | | 160.37 ± 5.240 |
Weight | | | 59.78 ± 8.084 |
BMI(kg/m2) | < 18.5 | 590(2.8) | 23.23 ± 2.834 |
| 18.5–23.9 | 13002(61.0) | |
| 24–27.9 | 6508(30.6) | |
| ≥ 28 | 1202(5.6) | |
Parity | 1 | 13211(62.0) | |
| 2 | 7348(34.5) | |
| 3 | 698(3.3) | |
| ≥ 4 | 45(0.2) | |
Education | ≤ 12 | 3834(18.0) | |
| ༞12 | 17468(82.0) | |
GWG | | | 12.88 ± 4.651 |
NW | < 4 | 20086(94.3) | 3.27 ± 0.516 |
| ≥ 4 | 1216(5.7) | |
NOF | 1 | 20860(97.9) | |
| ≥ 2 | 442(2.1) | |
DM | CS | 7664(36.0) | |
| NIVD | 10481(49.2) | |
| EP | 2600(12.2) | |
| FD | 557(2.6) | |
BMI body mass index, GWG gestational weight gain, NW neonatal weight, NOF number of fetus, DM delivery mode, CS cesarean section, NIVD non-instrumental vaginal delivery, EP episiotomy, FD forceps delivery |
Tonic contraction and Endurance contraction were inversely related with age. On the contrary, all the others variables except parity (≤ 3, rapid contraction only) had a positive impact on PFM strength include three types of contractions. In addition, CS also had protective effect on PFM strength (Table 2).
Table 2
Changes in rapid, tonic, and endurance contraction according to participants general characteristics in univariate analysis
Variables | Group | Rapid contraction | Tonic contraction | Endurance contraction |
| | Mean ± SD | P | | Mean ± SD | P | | Mean ± SD | P |
Age | ≤ 29 | 37.49 ± 17.70 | 0.420 | 26.38c ± 13.27 | < 0.001 | 22.22b ± 11.47 | < 0.001 |
| 30–39 | 37.82 ± 18.64 | | 25.75b ± 13.47 | | 21.55a ± 11.48 | |
| 40–49 | 37.91 ± 18.27 | | 23.81a ± 12.68 | | 20.53a ± 11.77 | |
BMI(kg/m2) | < 18.5a | 32.61 ± 15.12 | < 0.001 | 22.80 ± 11.75 | < 0.001 | 19.26 ± 10.19 | < 0.001 |
| 18.5–23.9b | 36.67 ± 17.68 | | 25.31 ± 12.83 | | 21.23 ± 11.08 | |
| 24–27.9c | 39.32 ± 18.60 | | 27.06 ± 14.17 | | 22.69 ± 11.96 | |
| ≥ 28d | 42.26 ± 21.70 | | 28.95 ± 14.50 | | 24.66 ± 12.89 | |
Parity | 1 | 36.98a ± 17.68 | < 0.001 | 25.92 ± 13.38 | 0.293 | 21.79 ± 11.52 | 0.445 |
| 2 | 38.83b ± 19.05 | | 26.12 ± 13.35 | | 21.85 ± 11.41 | |
| 3 | 39.02b ± 19.48 | | 25.90 ± 13.84 | | 22.09 ± 11.80 | |
| ≥ 4 | 33.63 ± 13.54 | | 22.717 ± 9.67 | | 19.32 ± 8.27 | |
Education | ≤ 12 | 36.89 ± 18.66 | 0.003 | 24.45 ± 12.93 | < 0.001 | 20.79 ± 11.08 | < 0.001 |
| ༞12 | 37.85 ± 18.14 | | 26.32 ± 13.45 | | 22.04 ± 11.56 | |
NW | < 4 | 37.51 ± 18.09 | < 0.001 | 25.86 ± 13.34 | < 0.001 | 21.69 ± 11.44 | < 0.001 |
| ≥ 4 | 40.43 ± 20.36 | | 28.04 ± 13.87 | | 23.93 ± 12.04 | |
NOF | 1 | 37.57 ± 18.21 | < 0.001 | 25.90 ± 13.35 | < 0.001 | 21.74 ± 11.46 | < 0.001 |
| ≥ 2 | 42.74 ± 19.06 | | 29.96 ± 14.22 | | 25.47 ± 12.17 | |
DM | CSd | 44.74 ± 18.88 | < 0.001 | 31.23 ± 14.01 | < 0.001 | 26.61 ± 12.09 | < 0.001 |
| NIVDc | 34.49 ± 16.85 | | 23.53 ± 12.11 | | 19.55 ± 10.25 | |
| EPb | 32.58 ± 15.49 | | 22.48 ± 11.61 | | 18.58 ± 9.84 | |
| FDa | 24.29 ± 13.29 | | 16.28 ± 10.44 | | 13.50 ± 8.71 | |
post-hoc test: a < b < c < d, BMI body mass index, GWG gestational weight gain, NW neonatal weight, NOF number of fetus, DM delivery mode, CS cesarean section, NIVD non-instrumental vaginal delivery, EP episiotomy, FD forceps delivery |
Stepwise regression analysis showed that Age and NW had a negative linear relation with rapid, tonic and endurance contraction (β=-.298, P < 0.001; β=-.354, P < 0.001; β=-.310, P < 0.001, respectively; β=-1.199, P < 0.001; β=-.380, P < 0.05; β=-.436, P < 0.01, respectively). Secundipara had a positive effect on rapid, tonic, and endurance contraction than primipara (β=-.055, P < 0.001; β=-.032, P < 0.001; β=-.029, P < 0.001, respectively). All factors showed even positive values in tertipara (β=-.025, P < 0.001; β=-.018, P = 0.010; β=-.021, P = 0.002, respectively). Contrarily, BMI, education and GWG (endurance contraction only) also showed a positive linear relation with three types of contraction (β = .546, P < 0.001; β = .366, P < 0.001; β = .309, P < 0.001, respectively; β = 2.767, P < 0.001; β = 3.141, P < 0.001; β = 2.391, P < 0.001, respectively; β = 0.046, P < 0.01). Participants with CS had a positive effect on rapid, tonic, and endurance contraction than participants with NIVD (β=-.292, P < 0.001; β=-.305, P < 0.001; β=-.324, P < 0.001, respectively); EP (β=-.216, P < 0.001; β=-.224, P < 0.001; β=-.239, P < 0.001, respectively); and FD (β=-.176, P < 0.001; β=-.182, P < 0.001; β=-.185, P < 0.001, respectively). (Table 3).
Table 3
Stepwise multiple linear regression analysis for the effect of independent variables on rapid, tonic, and endurance contraction
Variables | | Rapid contraction | Tonic contraction | Endurance contraction |
| | B | β | t | | B | β | t | | B | β | t |
(constant) | | 38.668 | | 24.032 | 28.967 | | 24.350 | 25.298 | | 24.770 |
Age | | − .298 | − .066 | -9.123*** | − .354 | − .107 | -14.860*** | − .310 | − .109 | -15.021*** |
BMI (kg/m2) | | .546 | .085 | 12.877*** | .366 | .078 | 11.826*** | .309 | .076 | 11.503*** |
Parity | 1 | (ref.) | | | (ref.) | | | (ref.) | | |
| 2 | 2.117 | .055 | 7.578*** | .905 | .032 | 4.438*** | .690 | .029 | 3.962*** |
| 3 | 2.553 | .025 | 3.650*** | 1.316 | .018 | 2.576* | 1.367 | .021 | 3.135** |
| ≥ 4 | | | | | | | | | |
Education | ≤ 12 | (ref.) | | | (ref.) | | | (ref.) | | |
| ༞12 | 2.768 | .058 | 8.743*** | 3.141 | .090 | 13.586*** | 2.391 | .080 | 12.116*** |
GWG | | | | | | | | .046 | .019 | 2.758** |
NW | | -1.199 | − .034 | -5.203*** | − .380 | − .015 | -2.258* | − .436 | − .020 | -2.964** |
NOF | 1 | (ref.) | | | (ref.) | | | (ref.) | | |
| ≥ 2 | | | | | | | | | |
DM | CS | (ref.) | | | (ref.) | | | (ref.) | | |
| NIVD | -10.639 | − .292 | -40.137*** | -8.169 | − .305 | -42.202*** | -7.445 | − .324 | -45.060*** |
| EP | -12.060 | − .216 | -30.245*** | -9.164 | − .224 | -31.470*** | -8.385 | − .239 | -33.729*** |
| FD | -20.159 | − .176 | -26.474*** | -15.238 | − .182 | -27.403*** | -13.342 | − .185 | -28.113*** |
F | | 281.255*** | | 304.462*** | | 304.302*** | |
R2 | | 0.106 | | | 0.114 | | | 0.125 | | |
adjR2 | | 0.106 | | | 0.114 | | | 0.125 | | |
BMI body mass index, GWG gestational weight gain, NW neonatal weight, NOF number of fetus, DM delivery mode, CS cesarean section, NIVD non-instrumental vaginal delivery, EP episiotomy, FD forceps delivery, B unstandardized beta, β standardized beta, t t test statistic, *p < .05, **p < .01, ***p < .001 |