Major or minor placenta previa: Does it make a difference?

Placenta previa is a severe pregnancy complication with considerable maternal and neonatal morbidity. Placenta previa can be defined as major or minor by location. Major placenta previa is associated with higher complication rates. Management of women with minor placenta previa has not been well defined. The primary goal of the study was to evaluate the accuracy of our existing screening protocol for placenta previa. Secondly, we wanted to compare pregnancy and delivery outcomes by the type of placenta previa.

The study was conducted at the Helsinki University Hospital between June 2010 and September 2014. The study population consisted of all women with the antenatal ultrasound diagnosis of placenta previa during delivery. Data were retrospectively collected and analysed.

Altogether 176 women had placenta previa at delivery (major 129, minor 47). Placenta previa remained undiagnosed at second trimester screening ultrasound in 32 women (18.2%). Twenty (62.5%) of these cases had minor placenta previa and 12 (37.5%) had major placenta previa. Five (15.6%) of the undiagnosed cases developed life-threatening hemorrhage (≥2500 ml) during the delivery and two had abnormally invasive placenta followed by hysterectomy. Women with major placenta previa had significantly more blood loss and delivered earlier than women with minor placenta previa. The groups were otherwise similar, including the rate of abnormally invasive placenta.

The existing protocol for placenta previa missed almost one fifth of cases. Both major and minor placenta previa are risk factors for abnormally invasive placenta and should be treated as severe conditions.