Maternal complications
The main variable exposed in our analysis was gestational age at delivery. The maternal complications were mainly episiotomy, instrumental delivery, intrapartum caesarean section (ICS), postpartum haemorrhage (PPH), shoulder dystocia, obstetric anal sphincter injury (OASIS), meconium-stained amniotic fluid (MSAF), intrapartum cervical laceration, epidural analgesia, amniotic fluid embolism and labour progression duration. An episiotomy performed at the time of crowning was defined as a surgical incision made to widen the vaginal opening for the delivery of the foetus11. Instrumental delivery was defined as vacuum extraction or forceps delivery12. In our hospital, it mainly referred to vacuum extraction. An international uniform standard of labour onset has not been established. Based on our combined physician experience, we defined ICS as emergency caesarean after regular uterine contractions, cervical canal flattening and cervix opening by 2+ cm for women who were attempting a vaginal delivery. According to the medical indication, the cephalopelvic disproportion group and foetal distress group were mainly compared. PPH was defined as blood loss in excess of 500 ml after vaginal delivery and in excess of 1000 ml after caesarean delivery in the first 24 hours after labour, and it was divided into mild PPH (estimated blood loss > 500 ml) and severe PPH (estimated blood loss > 1000 ml)13. The total amount of blood loss was measured by weighing soaked materials and by use of the suction system and collector bags in the operating room. Shoulder dystocia was defined as the inability of the foetus to be delivered by traditional midwifery methods when the symphysis pubis obstructed the anterior descending of the shoulder or the posterior shoulder of the foetus was impacted on the maternal sacral promontory14. OASIS, including third- and fourth-degree vaginal tears, damages the anal sphincter complex and anorectal mucosa15. Intrapartum cervical laceration was defined as laceration with abnormal vaginal bleeding or requiring cervical suturing16. Amniotic fluid embolism was defined as the abnormal activation of proinflammatory mediator systems triggered by entrance into the maternal circulation of material from the foetal compartment17. The first stage of labour was defined as beginning from maternal perception of regular contractions to dilation. The second stage of labour was defined as the time from full dilation to delivery of the neonate3.