Prolonged pregnancy complicates approximately 7% of all gestations. The most frequent cause of an apparently prolonged gestation is an error in dating. When postterm pregnancy truly exists, the cause usually is unknown. (ACOG,2004).
The incidence of obstetric & neonatal problems increases in pregnancies past 280 days of gestation, for each week of gestation after 40 weeks, the incidence of these complications increases significantly. (Ohel et al., 1995).
The perinatal mortality rate (stillbirths plus early neonatal deaths) at 42 weeks of gestation is twice that at 40 weeks and increases 4 fold at 43 weeks and 5 fold to 7 fold at 44 weeks. (Norwitz et al., 2007)
Complications of prolonged pregnancy include vacuum delivery, macrosomia, meconium-stained amniotic fluid, oligohydramnios , increase rates of cesarean delivery, retained placenta, birth injury, non-reassuring fetal heart rate and antepartum, intrapartum and postpartum deaths. Postterm pregnancy also is an independent risk factor for low umblical artery Ph levels at delivery and low 5 minute APGAR scores. Uteroplacental insufficiency, meconium aspiration, and intrauterine infection contribute to the increased rate of perinatal deaths. (Olesen., 2003)
maternal-fetal risks increase from 41 weeks and starting antenatal testing at 41 weeks of gestation may decrease the complications . Zeynep et al.,2009))
In the surveillance of the uncomplicated prolonged pregnancy, Doppler information may play a role in differentiating which pregnancies may be followed by expectant management or determine whether induction is a better option . (Palacio et al., 2004).
Combining the Doppler waveform analysis of the middle cerebral artery (MCA) with that of the umbilical artery (UA) by a common cerebroplacental ratio i.e. the ratio of their pulsatility indices has been
suggested as a useful clinical simplification. (Ebbing et al., 2007)
The cerebro umblical ratio shows a higher sensitivity (80%) in predicting adverse prenatal outcome when compared with the UA S/D ratio (56%) the UA PI (40%) and the MCA PI (50%). (El-Sokkary et al., 2011).
There is some studies indicate that cerebroplacental ratio is not predictive of unfavorable outcome in women with pregnancies lasting more than 41 weeks. ( D'Antonio et al., 2013).
The specificity of the AFI is high which indicates the probability of an adverse outcome such as meconium-stained amniotic fluid and hypoxia increases. (Khooshideh et al., 2009).
Amniotic fluid index of