Placenta praevia occurs when the placenta implants improperly in the lower uterine segment, covering or dangerously close to the internal cervical os. As the lower uterine segment stretches and thins in the late second and third trimesters, the placental attachment site is disrupted. This mechanical stretching tears the overlying blood vessels, leading to painless vaginal bleeding.
Several factors increase the likelihood of abnormal placental implantation by altering the endometrium. Previous uterine surgery creates scar tissue that can attract lower implantation.
Modern classification relies on ultrasound findings to describe how much of the internal cervical os is covered by placental tissue. This guides whether a vaginal delivery is possible or if a caesarean section is mandatory.
| Classification | Ultrasound Description |
|---|---|
| Major / Complete | Placenta completely covers the internal os |
| Partial | Placenta partially covers the internal os |
| Marginal | Placental edge reaches the margin of the internal os |
| Low-lying | Placenta is planted in the lower segment but not touching the os |
The classic presentation of placenta praevia is sudden, painless, bright red vaginal bleeding occurring after twenty weeks of gestation. The bleeding often stops on its own, only to recur later more heavily. Uterine tone remains soft and relaxed, without the painful woody rigidity seen in placental abruption. Fetal heart sounds are usually normal unless maternal blood loss is severe enough to cause shock.
A definitive diagnosis requires imaging rather than physical touch. Transabdominal ultrasound identifies placental location, but transvaginal ultrasound is safer and more accurate for measuring the precise distance from the internal os without disturbing the tissue.
Digital vaginal examinations are strictly contraindicated when unexplained bleeding occurs late in pregnancy, because inserting a finger can provoke catastrophic hemorrhage.
Management depends on gestational age and the volume of blood lost. If the fetus is premature and bleeding is minimal, conservative expectant management is chosen with hospital admission, bed rest, and serial blood counts. Corticosteroids are administered to mature fetal lungs.
If bleeding is severe or term is reached, immediate delivery via lower segment caesarean section is performed to save both mother and baby.
Midwives play a vital frontline role in monitoring stable inpatients and responding to emergencies. Essential care includes maintaining reliable intravenous access, monitoring vital signs for early signs of hypovolemic shock, and recording accurate fluid balance charts. Emotional reassurance is vital because prolonged hospital bed rest creates intense anxiety for expectant mothers and their families.
Placenta praevia carries severe risks including maternal haemorrhage, hypovolemic shock, emergency hysterectomy, and placental accreta spectrum where the placenta invades the uterine muscle. Midwives must activate emergency protocols immediately when heavy bleeding starts: call for senior help, crossmatch blood, administer oxygen, and prepare for rapid theater transfer.