Methods
The protocol for this study was approved by the Ethics Committee of the Japanese Red Cross Katsushika Maternity Hospital.
Subjects were women with vertex singleton pregnancy who delivered at Japanese Red Cross Katsushika Maternity Hospital between April 2008 and September 2012. In this study, cases of intrauterine fetal demise, cases of Cesarean deliveries before onset of labor pains or during the first stage of labor, cases of previous Cesarean deliveries and cases with severe maternal chronic heart disease were excluded. Data collected from delivery records included: patient’s age, parity, maternal complications such as pregnancy induced hypertension (PIH) and gestational diabetes mellitus (GDM), presence or absence of oligohydramnios (amniotic fluid index < 5 cm), gestational age at delivery, use of intravenous oxytocin, delivery modes, neonatal birth weight, neonatal Apgar score at 1 and 5 minutes, umbilical artery pH, shoulder dystocia, admission of neonatal intensive care units (NICU), third- or fourth-degree perineal laceration, presence or absence of cervical laceration, postpartum hemorrhage.
Pregnancy-induced hypertension was defined as blood pressure ≥ 140/90 mmHg measured on two or more occasions at least six hours apart with the patient at rest. A 75-g 2-hour oral glucose tolerance test was performed to diagnose gestational diabetes according to the Japan Society of Obstetrics and Gynecology. Gestational diabetes was defined as plasma glucose level meeting one of the following criteria: ≥ 92 mg/dL while fasting, ≥ 180 mg/dL after 1 hour, or ≥ 153 mg/dL after 2 hours. The fetus was considered to be as ‘non-reassuring fetal status (NRFS)’ if repeated late or severe variable deceleration (< 60 beats/minute and ≥ 60 seconds) and/or prolonged decelerations (< 100 beats/minute and ≥ 5 minutes) occurred.
In our hospital, UFPM is always performed by an obstetrician, and all the maneuvers were documented by the nursing staff. The UFPM during pushing stage of labor is performed with careful maternal observation and fetal heart rate monitoring.
Cases and controls were compared by the x2 or Fisher’s exact test for categorical variables. Odds ratios (ORs) and 95% confidence intervals (CIs) were also calculated. Differences with P < 0.05 were considered significant. Variables used in the multivariate model were those that on univariate analysis had shown significance toward association with UFPM. Logistic regression was then performed to identify the factors most strongly associated with UFPM in a multivariate model.