Comparison of demographic data between the Non-PPROM group and the PPROM group
Maternal weight in the first and second trimester and gestational age at testing in the second trimester were all significantly higher in the PPROM group than the control group (Z = 3.584, P < 0.001; Z = 3.491, P < 0.001; Z = 2.007, P = 0.045; respectively; Table 1). There was no significant difference with respect to maternal age, gestational age at testing in the first trimester between the two groups (P > 0.05)
Table 1
Comparison of demographic data between the non-PPROM group and the PPROM group.
Groups | Non-PPROM (n = 594) | PPROM (n = 591) | t or Z | P |
Maternal age (years) | 28.40 ± 2.85(28.17–28.63) | 28.64 ± 2.85(28.40–28.66) | 1.399 | 0.162 |
Maternal weight in the first trimester (kg) | 52.00(42.40–68.56) | 53.50(41.50–70.24) | 3.584 | < 0.001** |
Maternal weight in the second trimester (kg) | 53.50(43.50–69.41) | 55.00(43.00–71.30) | 3.491 | < 0.001** |
Gestational age at testing in the first trimester(days) | 90.00(80.00–97.00) | 90.00(79.00–97.00) | 0.397 | 0.691 |
Gestational age at testing in the second trimester(days) | 117.00(108.00–128.00) | 118.00(108.00–128.00) | 2.007 | 0.045* |
Note: Data are presented as median (P2.5–P97.5). PPRPOM, preterm prelabor rupture of membranes. *P < 0.05; **P < 0.001. |
Comparison of screening indicators (MOM) and the calculated risk of T21,T18
AFP and NT in the PPROM group were 1.03 MoM and 0.96 MoM in Table 2 and these were significantly higher than the Non-PPROM group (0.93MoM, Z=5.995, P < 0.001; 0.93 MoM, t = 2.352, P = 0.019, respectively). In addition, the calculated risk of T21 in the PPROM group was 1/15393 and this was higher than the Non-PPROM group (1/13714; Z = 1.438, P = 0.015). Conversely, the MoM for maternal PAPP-A, free β-hCG and the calculated risk of T18 in the PPROM group did not show any significant differences when compared with the Non-PPROM group.
Table 2
Comparison of screening indicators (MOM) and the calculated risk of T21,T18
Groups | Non-PPROM (n = 594) | PPROM (n = 591) | t or Z | P |
PAPP-A MoM | 0.95(0.33–2.41) | 1.00(0.28–2.35) | 0.707 | 0.480 |
Free β-hCG MoM in the first trimester | 1.07(0.34–3.48) | 1.02(0.39–3.44) | 0.381 | 0.703 |
NT MoM | 0.93 ± 0.25(0.90–0.95) | 0.96 ± 0.24(0.94–0.98) | 2.352 | 0.019* |
AFP MoM | 0.93(0.52–1.72) | 1.03(0.55–1.87) | 5.995 | < 0.001** |
Free β-hCG MoM in the second trimester | 1.03(0.34–3.49) | 1.02(0.36–3.77) | 0.741 | 0.459 |
Calculated risk of T21 | 1/13 714(1/339–1/100 000) | 1/15393(1/493–1/100 000) | 1.438 | 0.015* |
Calculated risk of T18 | 1/100 000(1/22092–1/100 000) | 1/100 000(1/13914–1/100 000) | 0.507 | 0.612 |
Data are presented as median (P2.5–P97.5). AFP, α-fetoprotein; hCG, human chorionic gonadotropin; PAPP-A, pregnancy-associated plasma protein A; NT, nuchal translucency; T21, trisomy 21; T18, trisomy 18; MoM, multiple of median. *P < 0.05; **P < 0.001. |
Results Of Binary Logistic Regression Analysis
Binary logistic regression analysis showed that the ORs and 95% CIs for maternal weight, AFP and NT were 1.030 (95%CI:1.011–1.049), 3.549 (95%CI:2.323–5.421) and 1.719 (95%CI:1.011–2.923) in Table 3, respectively, which were the risk factors of PPROM.
Table 3
Binary logistic analysis of maternal weight in the first trimester, AFP, NT and PPROM
Indicators | β | SE | Wald | df | P | OR | 95% CI for OR |
Lower | Upper |
Weight (kg) | 0.029 | 0.009 | 9.580 | 1 | 0.002* | 1.030 | 1.011 | 1.049 |
NT(MoM) | 0.542 | 0.271 | 4.002 | 1 | 0.045* | 1.719 | 1.011 | 2.923 |
AFP(MoM) | 1.267 | 0.216 | 34.336 | 1 | < 0.001** | 3.549 | 2.323 | 5.421 |
AFP, α-fetoprotein; NT, nuchal translucency; OR, the odds ratio; CI, confidence interval; SE, standard error; MoM, multiple of median; Weight, Maternal weight in the first trimester (kg). *P < 0.05; **P < 0.001. |
Predictive value of AFP, NT and maternal age separate screening and joint screening for PPROM
ROC analysis was performed to determine the predictive diagnosis value of maternal age, NT and AFP for PPROM (see Table 4 and Fig. 1). At the best cutoff level of 0.98 MoM, AFP predicted PPROM AUC = 0.618(95%CI: 0.583–0.653, P < 0.001), with a sensitivity, specificity and youden index of 0.583, 0.603, and 0.186, respectively. Besides, at the best cutoff level of 0.91 MoM, NT accurately predicted PPROM AUC = 0.552 (95%CI: 0.516–0.588, P = 0.005), with a sensitivity, specificity and youden index of 0.579, 0.531, and 0.111, respectively. After combining AFP, NT and maternal weight, the AUC increased to 0.630 (95%CI: 0.595–0.664, P < 0.001).
Table 4
The value of AFP, NT and maternal age separate screening and joint screening for PPROM.
Indicators | AUC | 95%CI | P | cut-off | Sensitivity | Specificity | Jordan index |
Weight (kg) | 0.556 | 0.520–0.592 | 0.002* | 52.45 | 0.591 | 0.517 | 0.108 |
NT(MoM) | 0.552 | 0.516–0.588 | 0.005* | 0.91 | 0.579 | 0.531 | 0.111 |
AFP(MoM) | 0.618 | 0.583–0.653 | < 0.001** | 0.98 | 0.583 | 0.603 | 0.186 |
Weight + NT + AFP | 0.630 | 0.595–0.664 | < 0.001** | 0.47 | 0.685 | 0.508 | 0.194 |
AFP, α-fetoprotein; NT, nuchal translucency; AUC: area under curve; CI, confidence interval; MoM, multiple of median; Weight, Maternal weight in the first trimester (kg); Predicted probability, Weight + NT + AFP. *P < 0.05; **P < 0.001. |