Data source and patients
The present was a single-center retrospective observational study. We reviewed and extracted medical records on singleton pregnancies and neonates between January 2016 and December 2020 at a tertiary perinatal medical center. We included all consecutive vaginal deliveries with MFP during the study period. MFP was conducted in strict accordance with the Japan Society of Obstetrics and Gynecology Guideline [17]: i) situations demanding urgent delivery to avoid unwarranted cesarean sections due to various fetal or maternal issues during the second stage of labor; ii) either alone or means to support vacuum-assisted or forceps delivery; iii) obstetrician or midwife stand on the side of the pregnant woman; iv) under intrapartum cardiotocography, applying pressure to the base of the uterus along the pelvic axis in synchrony with contractions; and v) a maximum duration of 20 minutes or a maximum number of 5 pushes. Details of each delivery were recorded immediately after birth and double-checked by the midwives. In the present study, multiple deliveries by the same patient during the study period were addressed as separate deliveries. We excluded the following cases: patients administered epidural analgesia, preterm births (<37 weeks of gestational age), breech deliveries or missing data. In Japan, epidural analgesia for labor is not common practice and accounts for less than 2% of cases in this study. In addition, while preterm birth is an important factor to consider, most preterm neonates are admitted to the neonatal intensive care unit (NICU) with or without resuscitation in our hospital and therefore were omitted from the present study. Our facility does not conduct forceps deliveries and trial of labor after cesarean deliveries.
Variables
Data on pregnancies and neonates in MFP-assisted vaginal deliveries included the following information: placental location, parity, maternal age, in-vitro fertilization, obstetric complications (hypertensive disorders of pregnancy and gestational diabetes mellitus), gestational age at delivery, indication for MFP, number of pushes attempted, vacuum-assisted delivery and neonatal birth weight. Placental location was categorized into four groups based on the second-trimester ultrasound and according to the location in which more than 60% attachment of the placenta was noted: posterior, lateral, anterior or fundal. The four placental locations were divided into two categories: posterior-lateral or anterior-fundal. These categories were adopted because the external force applied to the uterus during MFP could be more pronouncedly transmitted to the placenta in anterior and fundal placentation, which could mean greater risk for this category of patients. The number of pushes attempted to deliver the neonate was categorized into 1, 2 and ≥3 times. We categorized maternal age as <35 and ≥35 years and gestational age as 37–40 and >40 weeks. The indication for MFP was divided into three groups: i) prolonged second stage of labor which included a prolonged second stage with a clinically adequate pelvis, maternal exhaustion or persistent occiput posterior; ii) suspicion of immediate or potential fetal compromise which included fetal bradycardia; and iii) shortening of the second stage of labor for a maternal benefit which included maternal conditions indicating a need for shortening second stage or other indications, according to the American College of Obstetricians and Gynecologists and Royal Australian and New Zealand College of Obstetricians and Gynecologists Guidelines, respectively.[18] Neonatal birth weight was divided into three categories: ≤2500, 2501–3999 and ≥4000 g.
Outcomes
The primary outcome was an adverse neonatal composite including low umbilical artery blood pH (pH <7.2), Apgar score (Apgar score <7 at 5 min), NICU admission and neonatal resuscitation [14, 19]. The secondary outcome included maternal trauma (i.e., uterine rupture, rib fracture and organ injury), maternal transfusion, the amount of postpartum hemorrhage and postpartum hemorrhage ≥500 mL [1, 11, 12].
Statistical Analyses
Continuous variables were reported as the median and interquartile range (IQR). Categorical variables were reported as count and percentage and were compared using Fisher’s exact test. The Wilcoxon rank-sum test was applied for the analysis of continuous variables with skewed distribution. Multivariable logistic regression analysis was performed to examine the association between placental location and neonatal composite outcome with adjustment for parity, maternal age category, in‐vitro fertilization, hypertensive disorders of pregnancy, gestational diabetes mellitus, gestational age at delivery, indication for MFP, number of pushes attempted, vacuum-assisted delivery and neonatal birth weight category [15, 16]. The threshold for significance was a p-value of <0.05 and all tests were 2-tailed. All statistical analyses were conducted using Stata (Version 15.0, College Station, TX, USA).
Ethical Approval
This study obtained approval from the institutional review board of the Iida Municipal Hospital (approval number, 500-2) on 19 January 2021. Due to the anonymous nature of the data, the requirement for informed consent was waived.