Relationship between metalloproteinase-2 and -9 levels in plasma and vaginal secretion with preterm birth

To study the association of plasma and vaginal levels of matrix metalloproteinases 2 (MMP-2) and 9 (MMP-9), determined between 20⁺⁰ and 25⁺⁶ weeks of gestation, with preterm birth and its predictive value.

All 129 cases of preterm birth (cases) and 258 randomly selected term patients (control group) were included in a cohort study with a nested case-control design. Inclusion criteria were living in Ribeirão Preto, Brazil, and gestational age 20⁺⁰ to 25⁺⁶ at enrollment. Exclusion criteria were multiple fetuses, congenital malformations or chromosome syndromes, and loss to follow-up. Maternal age, parity, smoking, and previous preterm birth were included as covariates. A blood sample and vaginal secretion were obtained for the determination of MMP-2 and MMP-9; the patients were screened for urinary tract infection and bacterial vaginosis, and cervical length was measured by ultrasound. The cut-off values for matrix metalloproteinases were calculated using receiver operating characteristic (ROC) curves for logistic regression analysis (crude and adjusted odds ratios).

According to the WHO, in this study, preterm subtypes included 3.8 % extremely preterm, 6.9 % very preterm, and 89.2 % late preterm births. The plasma MMP-9 cut-off was 63.25 ng/mL and the area under the ROC curve was 0.725 (standard error 0.03; 95 % confidence interval, 0.677-0.769). The cut-off for plasma MMP-2 was 239.4 ng/mL and the area under the ROC curve was 0.585 (standard error 0.03, 95 % confidence interval, 0.521-0.649). Crude odds ratios showed an increased risk of preterm birth associated with plasma MMP-2 (odds ratio, 1.75; 95 % confidence interval, 1.14-2.68) and plasma MMP-9 (odds ratio, 3.26, 95 % confidence interval, 2.09-5.07); no association was detected for vaginal MMP-2 or 9. For plasma, adjusted odds ratios were 1.42 (95 % confidence interval, 0.80-2.53) for MMP-2 and 2.71 (95 % confidence interval, 1 .52-4.83) for MMP-9, along with an increased risk in other covariates.

Elevated plasma MMP-9 levels and decreased MMP-2 levels were positively associated with preterm birth. Plasma MMP-9 level increased nearly three times the preterm risk.