Obstetric outcome in post-term pregnancies: time for reappraisal in clinical management.

Background: The objective of this study was to determine the outcome of pregnancy in post-term cases compared with term cases in a well defined population receiving modern obstetric care.

Methods: We utilized the population-based birth registry data of the Kuopio University Hospital (1990-2000) to investigate pregnancy outcome in 1,678 post-term singleton pregnancies. The general obstetric population (n=22,712) was used as a reference group in logistic regression analysis.

Results: The overall frequency of post-term pregnancies was 6.9% and the incidence of post-term pregnancies was found to be increased in obese, primiparous, and smoking women, whereas in women with chronic diseases and obstetric risks deliveries were induced earlier. The risks of macrosomia, maternal complications, and operative deliveries were increased in post-term pregnancies. Post-term infants experienced meconium passage (21.2% versus 12.8%) (p<0.01) and intrapartum asphyxia (3.4% versus 2.1%) (p<0.01) significantly more often than the controls. However, the stillbirth rate was low, probably due to careful monitoring of these pregnancies.

Conclusions: Although high-risk pregnancies were not allowed to come post-term, postmaturity per se is a moderate risk state compromising fetal well-being with regard to meconium passage and acid-base status at birth. We conclude that simple antenatal monitoring beyond 42 weeks reduces perinatal mortality but is inefficient in reducing meconium-stained liquor seen with increasing gestation.