Placenta praevia

What it is

Antepartum hemorrhage is bleeding after 24 weeks of gestation, reported in another source as vaginal bleeding from 20 wk to term, and placenta previa is one of its causes, along with idiopathic bleeding, coagulopathy, placental abruption, vasa previa, local causes such as a cervical polyp, laceration, ectropion or cancer, preterm labour and uterine rupture. The same differential is also ordered by how common each cause is, with bloody show, which represents cervical changes and the early stages of dilation, as the most common etiology in T3, and abruptio placentae as the most common pathological etiology in T3. Placenta previa is classified by how much of the internal os the placenta reaches:

• Minor degree, type 1, low lying placenta: placenta edge 2 cm or more from the internal os
• Minor degree, type 2, marginal: the placenta touches the margin of the internal os
• Major degree, type 3, partial: the placenta partially covers the internal os
• Major degree, type 4, complete: the placenta completely covers the internal os

The incidence is 0.5%, and it causes 20% of antepartum hemorrhages; it is also given as 3.5 to 4.6 per 1000 births. Most low-lying placentas are not praevia at delivery: 5% will have a low-lying placenta when scanned at 16-20 weeks gestation, while the incidence at delivery is only 0.5%, so most placentas rise away from the cervix. Another page gives 0.5-0.8% of all pregnancies, against 1-2% for abruptio placentae.