Post term labour is seen in:
Causes of Post-term pregnancy:

Wrong dates: due to inaccurate LMP (most common).
Biologic variability (Hereditary) may be seen in the family.
Maternal factors: Primipara/elderly multipara/H/o previous prolonged pregnancy, sedentary habit.
Fetal factors: Congenital anomalies: Anencephaly – (Abnormal fetal HPA axis), adrenal hypoplasia (Diminished fetal cortisol response).
Placental factors: Sulphatase deficiency (Low oestrogen).
Hydramnios
PID
Anencephaly
Multiple pregnancy