Figure 1 shows the inclusion of the study participants. During the study period, there were 1,967 deliveries at Fukushima Medical University Hospital. Among them, histopathological examination of the placenta was performed in 778 cases; of these, 212 and 44 cases were excluded because of multiple pregnancies and delivery before 22 weeks, respectively. Furthermore, 43, 62, 37, 24, 30, and 9 cases were excluded because of clinical CAM, hypertensive disorders of pregnancy, placental abruption, placenta accreta spectrum, non-reassuring fetal status, and intrauterine fetal death, respectively. As a result, 317 cases were eligible for the final analysis. They were categorized as “LD” (n = 83), “SPTB” (n = 144), and controls (n = 90), which included 53 and 37 cases of fetal anomaly and growth restriction and delivery without UC, respectively.
Table 2 shows the basic characteristics of the women in the three groups. Both mean maternal age and maternal age category were significantly different among the groups. The LD group tended to have more patients aged 30–39 years. The rates of primipara and CS delivery in the LD group were 91.6% and 83.1%, respectively, and were significantly higher than those of the SPTB and control groups (P < 0.01 and P < 0.05, respectively). The mean (standard deviation) gestational age at delivery in patients in the LD, SPTB, and control groups was 39.6 (1.2), 30.7 (5.1), and 35.9 (3.4) weeks, respectively, which were significantly different (P < 0.001). Although the incidence of umbilical cord artery (UmA) pH < 7.20 was not significantly different among the three groups (P = 0.310), the mean pCO2, pO2, and base excess (BE) in the UmA were significantly different (P < 0.05, P < 0.01, and P < 0.01, respectively).
Table 2
Basic maternal characteristics of the LD, SPTB, and control groups
| Participants | |
| LD | SPTB | Control | |
Variable | n = 83 | n = 144 | n = 90 | P-value |
Maternal age, years | 34.2 (5.8) | 31.9 (6.2) | 31.4 (6.1) | < 0.01a |
Maternal age category, % | | | | |
< 30 years | 24.1 | 34.7 | 38.9 | < 0.05b |
30–39 years | 54.2 | 56.9 | 52.2 |
> 40 years | 21.7 | 8.3 | 8.9 |
Maternal height, cm | 157 (6.0) | 158 (5.9) | 158 (5.8) | 0.343a |
Primipara, % | 91.6 | 47.2 | 58.9 | < 0.01b |
Cesarean section, % | 83.1 | 64.6 | 66.7 | < 0.05b |
Gestational age at delivery, weeks | 39.6 (1.2) | 30.7 (5.1) | 35.9 (3.4) | < 0.01a |
Birth weight at delivery, g | 3143 (398) | 1637 (836) | 2160 (770) | < 0.01a |
Results are expressed as mean (standard deviation) unless specified otherwise. |
LD: labor dystocia, SPTB: spontaneous preterm birth. |
aP-value: one-way analysis of variance. |
bP-value: chi-squared test. |
Table 3 shows the incidence of hCAM and funisitis and their grades in the LD, SPTB, and control groups. The incidence of hCAM and funisitis in the control group was 14.4% and 3.4%, respectively. The incidence of hCAM and funisitis in the LD group was 63.9% and 39.2%, respectively, which were significantly higher than those of the other two groups. The incidence of hCAM and funisitis ≥ stage 2 were also the highest in the LD group (54.2% and 34.9%, respectively)
Table 3
The grade of CAM and funisitis in LD, SPTB, and control groups
| Participants | |
| LD | SPTB | Control | |
Variable | n = 83 | n = 144 | n = 90 | P-valuea |
CAM, % | 63.9 | 52.1 | 14.4 | < 0.01 |
CAM stage, % | | | | |
0 | 36.1 | 47.9 | 85.6 | < 0.01 |
1 | 9.6 | 14.6 | 6.7 |
2 | 24.1 | 13.2 | 1.1 |
3 | 30.1 | 24.3 | 6.7 |
CAM stage ≥ 2, % | 54.2 | 37.5 | 7.8 | < 0.01 |
Funisitis, % | 39.2 | 24.8 | 3.4 | < 0.01 |
Funisitis stage, % | | | | |
0 | 60.2 | 75.2 | 96.6 | < 0.01 |
1 | 4.8 | 5.0 | 2.3 |
2 | 19.3 | 7.1 | 1.1 |
3 | 15.7 | 12.8 | 0.0 |
Funisitis stage ≥ 2, % | 34.9 | 19.9 | 1.1 | < 0.01 |
CAM: chorioamnionitis, LD: labor dystocia, SPTB: spontaneous preterm birth. |
aP-value: chi-squared test. |
Table 4 shows the comparisons of the results of the UmA gas analysis at delivery between the LD and control groups. Both the mean UmA pH and incidence of UmA pH < 7.20 were not significantly different between the two groups (P = 0.465 and P = 0.213, respectively). The mean UmA CO2 was significantly higher in the control group (44.7 vs. 48.6 mmHg, respectively, P < 0.01), whereas the mean BE was significantly higher in the LD group (-5.1 vs. -4.0, respectively, P < 0.01).
Table 4
Comparison of UmA gas analysis at delivery between LD and control groups
| Participants | |
| LD | Control | |
Variable | n = 83 | n = 87 | P-value |
pH | 7.30 (0.06) | 7.29 (0.07) | 0.465a |
pH < 7.20, % | 3.6 | 9.2 | 0.213b |
pCO2, mmHg | 44.7 (8.0) | 48.6 (10.0) | < 0.01a |
pO2, mmHg | 17.7 (6.0) | 17.4 (6.6) | 0.781a |
BE, mmol/L | -5.1 (2.8) | -4.0 (3.2) | < 0.05a |
Results are specified as mean (standard deviation) unless specified otherwise. |
LD: labor dystocia, BE: base excess, UmA: Umbilical artery |
aP-value: t-test. |
bP-value: chi-squared test. |
Table 5 shows the comparisons of labor duration between LD cases classified based on the presence or absence of histological inflammation. Mann–Whitney U test showed that there was no significant difference in the labor duration between the cases with and without inflammation, such as hCAM, hCAM stage ≥ 2, funisitis, and funisitis stage ≥ 2 (P = 0.837, P = 0.790, P = 0.476, and P = 0.211, respectively).
Table 5
Comparison of labor duration based on the presence or absence of intrauterine inflammation in LD
| Positive | Negative | P-valuea |
CAM, n | 51 | 30 | |
hours, median (IQR) | 9 (6–14) | 8 (7–14) | 0.837 |
CAM stage ≥ 2, n | 44 | 37 | |
hours, median (IQR) | 9 (6–14) | 8 (7–15) | 0.79 |
Funisitis, n | 33 | 48 | |
hours, median (IQR) | 9 (6–14) | 9 (7–14) | 0.476 |
Funisitis stage ≥ 2, n | 29 | 52 | |
hours, median (IQR) | 8 (6–14) | 9 (7–16) | 0.211 |
LD: labor dystocia, CAM: chorioamnionitis, IQR: interquartile range. |
aP-value: Mann–Whitney U test. |
Table 6 shows the association between LD, SPTB, and intrauterine inflammation. LD was a risk factor for hCAM (aOR: 6.3, 95% CI: 1.9–20.5), hCAM stage ≥ 2 (aOR: 6.0, 95% CI: 1.7–21.8), funisitis (aOR: 9.4, 95% CI: 1.8–48.2), and funisitis stage ≥ 2 (aOR: 23.5, 95% CI: 2.3-238.8). SPTB was also a risk factor for hCAM (aOR: 3.7, 95% CI: 1.7–7.8), hCAM stage ≥ 2 (aOR: 2.8, 95% CI: 1.2–7.9), and funisitis (aOR: 4.5, 95% CI: 1.2–16.8).
Table 6
The risk of intrauterine inflammation in LD and SPTB
| CAM | CAM ≥ 2 | Funisitis | Funisitis ≥ 2 |
LD (+) OR (95% CI) | 10.5 (5.0–21.9) | 14.1 (5.8–34.0) | 18.7 (5.4–64.1) | 46.7 (6.2–353.0) |
LD (+) aOR (95% CI) | 6.3 (1.9–20.5) | 6.0 (1.7–21.8) | 9.4 (1.8–48.2) | 23.5 (2.3–238.8) |
SPTB (+) OR (95% CI) | 6.0 (3.1–11.5) | 6.3 (2.8–13.9) | 7.0 (2.4–20.5) | 10.8 (2.5–46.5) |
SPTB (+) aOR (95% CI) | 3.7 (1.7–7.8) | 3.0 (1.2–7.9) | 4.5 (1.2–16.8) | 7.4 (0.9–61.6) |
CAM, chorioamnionitis, LD: labor dystocia, SPTB: spontaneous preterm birth, OR: odds ratio, aOR: adjusted odds ratio, CI: confidential interval. |
aOR was calculated accounting for maternal age (< 30 years as reference), parity (0: primipara, 1: multipara), mode of delivery (0: cesarean delivery, 1: vaginal delivery), gestational age (continuous variable), and duration of labor (continuous variable). |