The exact cause of<unk>  is unknown. It is hypothesized to be related to abnormal vascularisation of the endometrium caused by scarring or atrophy from previous trauma, surgery, or infection. These factors may reduce differential growth of lower segment, resulting in less upward shift in placental position as pregnancy advances. Risk factors +Risk factors with their odds ratio Risk factor Odds ratio Maternal age ≥ 40 (vs. < 20) 9.1 Illicit drugs 2.8 ≥ 1 previous Cesarean section 2.7 Parity ≥ 5 (vs. para 0) 2.3 Parity 2–4 (vs. para 0) 1.9 Smoking 1.6 Congenital anomalies 1.7 Male fetus (vs. female) 1.1 Pregnancy-induced hypertension 0.4 The following have been identified as risk factors for<unk> : *Previous<unk>  (recurrence rate 4–8%), caesarean delivery, myomectomy or endometrium damage caused by D&C. *Women who are younger than 20 are at higher risk and women older than 35 are at increasing risk as they get older. *Women who have had previous pregnancies (multiparity), especially a large number of closely spaced pregnancies, are at higher risk due to uterine damage. *Smoking during pregnancy; cocaine use during pregnancy *Women with a large placentae from twins or erythroblastosis are at higher risk. *Race is a controversial risk factor, with some studies finding that people from Asia and Africa are at higher risk and others finding no difference. * Placental pathology (velamentous insertion, succenturiate lobes, bipartite i.e. bilobed placenta etc.) * Baby is in an unusual position: breech (buttocks first) or transverse (lying horizontally across the womb).<unk>  is itself a risk factor of placenta accreta. Alcohol use during pregnancy was previously listed as a risk factor, but is discredited by this article. Classification Traditionally, four grades of<unk>  were used, but it is now more common to simply differentiate between "major" and "minor cases. Type Description Minor Placenta is in lower uterine segment, but the lower edge does not cover the internal os Major Placenta is in lower uterine segment, and the lower edge covers the internal os Other than that<unk>  can be also classified as: Complete: When the placenta completely covers the cervix Partial: When the placenta partially covers the cervix Marginal: When the placenta ends near the edge of the cervix, about 2 cm from the internal cervical os
Placenta praevia
Placental abruption
Toxic abortion
Prelabor rupture of membranes
Septic abortion
Obstructed labour
Uterine rupture
Unsafe abortion