Timing of elective caesarean section and wet lung syndrome

1. Elective versus emergency caesarean section

  • Elective caesarean section refers to a planned operation prior to an onset of labour. An emergency caesarean section is the opposite. Some originally may plan for vaginal delivery but need an emergency caesarean section in the end. Others may have already scheduled an elective caesarean section but end up having an emergency operation due to onset of labour or antenatal complications;
  • It has been consistently shown that emergency caesarean section is associated with higher maternal and neonatal morbidities compared with elective cases;
  • If it is decided that caesarean section is indicated, it is preferable to schedule it prior to the onset of labour as long as it is safe

2. Risks of scheduling the elective caesarean section too early

  • Neonatal wet lung syndrome- the lack of stress of labour might be associated with a poorer ability of expulsion of the lung fluid by the baby upon delivery. It is called ‘transient tachypnoea of newborn’. The affected baby shows difficulty with breathing and the treatment is by oxygen therapy. It usually takes a few days to recover. Occasionally, support for breathing is required for severe cases;
  • The risks of having transient tachypnea of newborn following an elective caesarean section are related to the gestational age at operation: 3% for 39 and 40 weeks of gestation, 5% for 38 weeks and 8% for 37 weeks

3. When should elective caesarean section be scheduled?

  • The best timing of an elective caesarean section is a balance between the probability of neonatal wet lung syndrome versus the risks of requiring an emergency operation;
  • Elective caesarean section should be scheduled at 39 weeks or after according to both the American College of Obstetricians and Gynecologists and the Royal College of Obstetricians and Gynaecologists in the UK;
  • Based on the data of one public hospital in Hong Kong between 1995 and 2009 involving 87,000 low risk women, the probabilities of spontaneous labour prior to 37, 38 and 39 weeks of gestations were 4.7%, 12.7% and 33% respectively (Personal communication from Professor TY Leung, Department of O&G, CUHK). Therefore, if all caesarean sections are scheduled after 39 weeks of gestation, approximately 1 in 3 cases will become emergency operations. If they are scheduled at 38 weeks of gestation, the risks of emergency would have dropped to 1 in 8;
  • The above information should be presented to the women when they choose the date of their elective caesarean section. In general, the date should be closer to 39 weeks;
  • For those pregnancies with significant morbidities in case of onset of labour, the date should be scheduled earlier. One example is placenta previa;
  • Also, the perinatal mortality of twins increases after 38 weeks of gestation. So, for twin pregnancy, an elective caesarean section should be scheduled before  38 weeks

4. Role of antenatal steroids before elective caesarean section
Steroids given to the mother may hasten the lung maturity of the baby. Three randomised controlled studies have demonstrated lower neonatal respiratory morbidity with antenatal steroids before elective caesarean section at 37-39 weeks. The effects are more prominent between 37-38 weeks. The long-term side-effects of antenatal steroids are not fully known yet although data from randomized controlled trials for preterm infants are reassuring.


This article is contributed by Dr. T.N. Danny Leung
Updated on 25.09.2020