The demographic characteristics of the two groups were not significantly different. A total of 359 asymptomatic singleton pregnancies where the CL was between 10 mm and 30 mm were initially included in this study. Of these, 92 cases were excluded from the analysis: 83 because they were medically indicated for preterm delivery and nine because they underwent pessary placement. Finally, a total of 267 singleton pregnant women, of which 116 had cervical cerclage and 151 had vaginal progesterone, were retrospectively analyzed (Fig. 1).
The baseline characteristics of mean gestational age (30.0 vs. 31.0 weeks), body mass index (23.67 ± 3.53 vs. 23.82 ± 3.34 kg/m2), CL measurement before treatment (18 mm vs. 20 mm), white blood cell count (9.1 vs. 9.2), percentage of neutrophils (75.85 vs. 76.00), and other related medical histories (previous preterm delivery, cervical injury, and pregnancy complications) were similar between women in the cerclage group and those in the control group. The baseline characteristics of the two groups were therefore not significantly different (Table 1). The HR and OR for each of the primary and secondary outcomes are shown in Table 2.
Table 1
Baseline characteristics of the maternal participants
Characteristic
|
Cervical cerclage group (n = 116)
|
Vaginal progesterone group (n = 151)
|
t/Z/χ2
|
P
|
Age, median (IQR)
|
30.00 (28.00, 34.00)
|
31.00 (28.00, 34.00)
|
−0.569
|
0.570
|
BMI, mean ± SD
|
23.67 ± 3.53
|
23.82 ± 3.34
|
0.347
|
0.729
|
CL measurement before treatment (cm), median (IQR)
|
1.80 (1.50, 2.40)
|
2.00 (1.40, 2.20)
|
−0.453
|
0.650
|
White blood cell count, median (IQR)
|
9.10 (7.90, 11.38)
|
9.20 (7.60, 11.13)
|
−0.349
|
0.727
|
Percentage of neutrophils, median (IQR)
|
75.85 (72.93, 80.30)
|
76.00 (72.98, 79.18)
|
−0.124
|
0.901
|
Pregnancy complications (%)
|
|
|
2.637
|
0.104
|
No
|
93 (80.2)
|
108 (71.5)
|
Yes
|
23 (19.8)
|
43 (28.5)
|
Previous history of cervical injury (%)
|
|
|
0.007
|
0.932
|
No
|
111 (95.7)
|
143 (94.7)
|
Yes
|
5 (4.3)
|
8 (5.3)
|
Previous history of PTB (%)
|
|
|
0.038
|
0.450
|
No
|
109 (94.0)
|
141 (93.4)
|
Yes
|
7 (6.0)
|
10 (6.6)
|
Membranes ruptured before treatment (%)
|
|
|
0.118
|
0.732
|
No
|
103 (88.8)
|
132 (87.4)
|
Yes
|
13 (11.2)
|
19 (12.6)
|
BMI, body mass index; CL, cervical length; IQR, interquartile range; PTB, preterm birth; SD, standard deviation. |
Table 2
Primary and secondary outcomes in the cerclage and vaginal progesterone groups
|
Model 1* crude
|
P crude
|
Model 2#-adjusted
|
P-adjusted
|
Primary outcome
|
|
|
|
|
Delivery < 28a
|
4.147 (1.863, 9.234)
|
0.001
|
4.195(1.868, 9.421)
|
0.001
|
Delivery < 32a
|
2.738 (1.626, 4.609)
|
0.001
|
2.957 (1.743, 5.018)
|
0.001
|
Delivery < 34a
|
2.653(1.663,4.231)
|
0.001
|
2.897 (1.803, 4.655)
|
0.001
|
Delivery < 37a
|
1.529 (1.076, 2.172)
|
0.018
|
1.739 (1.213, 2.494)
|
0.003
|
Secondary outcomes
|
|
|
|
|
Neonatal mortalitya
|
3.519 (1.364, 9.079)
|
0.009
|
3.513 (1.350, 9.145)
|
0.010
|
Latency period from diagnosis to deliveryb
|
39.840 (29.827,49.853)
|
0.001
|
38.486 (29.295,47.678)
|
0.001
|
Hemorrhage during delivery (ln-trans)b
|
−0.084 (− 0.233, 0.066)
|
0.271
|
−0.064 (− 0.207, 0.080)
|
0.384
|
Birth weightc
|
0.370 (0.224, 0.610)
|
0.001
|
0.332 (0.196, 0.561)
|
0.001
|
Cesarean deliveryd
|
0.844 (0.510, 1.397)
|
0.509
|
0.836 (0.499, 1.400)
|
0.496
|
Notes: |
a: Cox semiparametric regression model; b: generalized linear regression model; c: ordinal logistic regression model; d: binary logistic regression model; |
* Model 1; # Model 2 |
Model 1, the univariate analysis that only incorporated the treatment method, showed that compared with the vaginal progesterone group, the cerclage group had a higher risk of PTB at < 37 weeks (HR, 1.529; 95% confidence interval [CI] 1.076–2.172), < 34 weeks (HR, 2.653; 95% CI 1.663–4.231), < 32 weeks (HR, 2.738; 95% CI 1.626–4.609), and < 28 weeks (HR, 4.147; 95% CI 1.863–9.234) of gestation.
Model 2 was the multivariable Cox risk factor regression model adjusted for potential confounders (age, body mass index, CL measurement before treatment, white blood cell count, percentage of neutrophils, pregnancy complications, history of cervical injury, history of PTB, and ruptured membranes before treatment). This analysis showed a more prominent correlation between cervical cerclage and PTB. Compared with the vaginal progesterone group, the cerclage group had an increased risk of PTB at < 37 weeks (HR, 1.739; 95% CI 1.213–2.494), < 34 weeks (HR, 2.897; 95% CI 1.803–4.655), < 32 weeks (HR, 2.957; 95% CI 1.743–5.018), and < 28 weeks (HR, 4.195; 95% CI 1.868–9.421) of gestation, latency period from diagnosing to delivery (β 38.486; 95% CI 29.295–47.678), and neonatal mortality (HR, 3.513; 95% CI 1.350–9.145). Furthermore, the cerclage group was associated with a higher risk of low birth weight (OR 0.370, 95% CI 0.244–0.610). Notably, in the ordinal logistic regression for birth weight, OR represents the risk or quantitative relationship of the outcome with a larger assignment (the birth weight is assigned as follows: less than 1,500 g = 1; 1,500–2,500 g = 2; greater than 2,500 g = 3). There was no statistical significance in the variables hemorrhage during delivery and cesarean delivery.
The Kaplan-Meier plots displayed a statistically significant difference in PTB at < 37, <34, < 32, and < 28 weeks of gestation between the cerclage and vaginal progesterone curves (P < 0.05) overall (Figs. 2, 3, 4, and 5).