All the following can be a cause for obstruction of after coming head of breech Except:

Ans. b. (Placenta previa). (Ref. Dutta Obstetrics 5th ed. 402)BREECH PRESENTATION# Most common type is complete breech in multipara and frank breech (70%) in primi.# Prematurity is the commonest cause.# Other causes are uterine malformations (recurrent breech) and hydrocephalus.# Denominator--sacrum# Commonest positions--left sacroanterior# Perinatal mortality rate is 3-10% in uncomplicated breech.# Foetal mortality is least in frank breech and maximum in footling presentation.# Gynaecoid and anthropoid pelvis are favourable for after coming head of breech.# After coming head of breech is an indication for external cephalic versionThere is no consensus that after coming head of breech can be obstructed by placenta previa.PLACENTA PREVIA# Placenta implanted wholly or partially in the lower uterine segment. 28% of women scanned before 24 weeks gestation have a low lying placenta - 3% at term.# Trans-vaginal scanning improves accuracy of diagnosis of placenta previa especially with posterior placenta.- If the placenta encroaches or covers the internal cervical os then there is MAJOR placenta previa otherwise there is MINOR placenta previa. This has replaced grades I - IV.# Risk factors- Increasing maternal age / smoking / previous caesarean section / previous placenta previa - 4-8% recurrence risk# Maternal risks- Haemorrhage related mortality- PPH- Complications of caesarean section post-partum sepsis- Placenta accreta (up to 15% of placenta previa)Recurrence risk# Fetal risks- Prematurity- IUGR- Congenital malformations (double risk of serious malformation)- Mal-presentation.