This study retrospectively analysed 73 singleton pregnancy cases diagnosed with pPROM during the gestational period from 22 weeks and 0 days to 27 weeks and 6 days. These cases were selected from 4833 cases who underwent delivery at our hospital from April 2013 to March 2018. The target patient population consisted of pregnant women who had been seen at our hospital from the beginning of pregnancy, and patients who were transferred to our hospital because of pPROM. From there, we limited the cases in which the maternal and neonatal course could be confirmed retrospectively.
The following patient background factors were analysed: mother’s age, previous delivery, delivery method (vaginal delivery or caesarean section), the administration of betamethasone to the mother, the gestational week at which a diagnosis of pPROM was made, time of delivery, oligohydramnios, and the presence of clinical CAM as a complication. Also, the following factors were analysed for perinatal prognosis: neonatal weight, APGAR score, umbilical arterial blood pH, small for gestational age (SGA) as a complication, neonatal death, use of mechanical ventilation management, neonatal sepsis as a complication, CAM stage in pathologic examination of the placenta, and BPD as a complication. Expected date of confinement was determined from the last menstrual period and ultrasonography of the first trimester.
Diagnosis definition
The diagnosis of pPROM was made through a combination of the following methods: checking leaked amniotic fluid in speculum examination; basic pH testing; and quantitative testing for amniotic proteins. Oligohydramnios was defined as an amniotic fluid index (AFI) of less than 5 cm on transabdominal ultrasonography. Regarding the duration of oligohydramnios, it was assumed that it did not start at the time when the fluid was actually ruptured, but at the time when the oligohydramnios was detected by ultrasonography at a medical institution.
Blanc's classification (6) was adopted in staging CAM in the pathological examination of the placenta. The most severe stage in this classification is Stage III, which is defined as a case in which the presence of inflammatory cells in the amniotic membranes is observed in pathological examination.
Diagnostic criteria by the National Institute of Child Health and Human Development (NICHD) (7) were adopted in making a diagnosis of BPD. In other words, a diagnosis of BPD was made when the administration of oxygen at a fraction of inspiratory oxygen (FiO2) >21 was required for a duration of 28 days or longer.
In these cases, preterm infants were delivered in the presence of a neonatal doctor. Depending on the respiratory condition of the newborn, intubation management was performed, and he was admitted to the neonatal intensive care unit and underwent artificial respiration management.
pPROM treatment procedure
This section explains a treatment plan at our hospital for cases diagnosed with pPROM before 28 weeks of gestation. A blood test was performed, especially for white blood cell count, when a case was diagnosed with pPROM. If it was confirmed that the mother was not complicated by clinical CAM, details of which were given below, a total of two doses of 12 mg of betamethasone was administered to the mother every 24 hours. Ritodrine hydrochloride, magnesium sulphate or a combination of these were consecutively administered as a tocolytic agent. For antibiotic therapy, 6 g/day of ampicillin/sulbactam (ABPC/SBT) was administered for one week following the diagnosis of pPROM. The well-being of the foetus were evaluated on NST two to four times a day. The patterns of foetal heart rate was evaluated each time. The mother was required to rest in bed, and an indwelling urinary catheter was inserted. The mother was closely monitored for deep venous thrombosis if she was required to rest in bed for an extended period of time. Provided that pregnancy could be prolonged by approximately two weeks, the level of rest might be increased. Foetal ultrasonography was performed weekly to evaluate the growth of the foetus; transabdominal ultrasonography was performed twice weekly to evaluate the amount of amniotic fluid.
The early delivery of the foetus was determined in the following cases: 1. diagnostic criteria for clinical chorioamnionitis were met; or 2. a diagnosis of NRFS was made based on foetal heart rate monitoring. Criteria by Lencki and colleagues (8) was used when making a diagnosis of clinical chorioamnionitis. According to the criteria, a case was diagnosed with the condition if the mother had a temperature of 38 °C or higher and exhibits any of the following conditions: 1. a tachycardia at a rate ≥100 bpm; 2. a tender uterus; 3. odour from vaginal discharge/amniotic fluid; or 4. a white blood cell count ≥15000/µL. Alternatively, a case was diagnosed with the condition if the mother exhibited all of the above four conditions while her body temperature was lower than 38 °C.
In these cases, preterm infants were delivered in the presence of a neonatologist. Depending on the respiratory condition of the newborn, intubation management was performed, and they were admitted to the neonatal intensive care unit and underwent artificial respiration management.
Statistical analysis
IBM SPSS Statistics for Windows, version 25® (IBM Corp., Armonk, N.Y., USA) was used for statistical analysis. The χ2 test, t-test and Fisher’s exact test were used in two-group comparison; multiple logistic regression analysis was used for multivariate analysis. The following variables were considered confounding factors: gestational age at delivery, oligohydramnios, CAM stage III in pathologic examination of the placenta, small for gestational age, the male sex of the neonate, and the use of positive pressure ventilation after birth. The level of statistical significance was set at p <0.05. The cut-off value for the receiver operating characteristic (ROC) curve was set by using Youden’s index (9). In this method, the cut-off point is defined as the point where the sum of the levels of sensitivity and specificity(10) reaches its maximum on the ROC curve. At our hospital, termination of pregnancy is determined when a case is diagnosed with clinical CAM. Hence, 16 cases who were diagnose with clinical CAM during pregnancy were excluded from analysis in which the ROC curve was used. The remaining 57 cases were analysed.
In this study, we used multivariate analysis (multiple logistic analysis) including known confining factors such as preterm labor, oligohydramnios, chorioamnionitis, small for gestational age, male sex of the neonate, and use of positive pressure ventilation after birth. It was analyzed after including it.