Placenta previa is defined as a condition in which placenta is implanted partially over the lower uterine segment. About 35% of cases of antepartum hemorrhage is due to placenta previa and it’s incidence ranges from 0.5 to 1% amongst hospital deliveries. Multiparous women are at high risk of developing placenta previa. Women beyond 35 years, with high birth order pregnancies and multiple pregnancies are at high risk of developing placenta previa.
Theories postulated for placenta previa
- Dropping down theory suggest the formation of central placenta previa as the fertilized ovum drops down and is implanted in lower uterine segment.
- Lesser degree of placenta previa is associated with persistence of chorionic activity of deciduas capsularis.
- Defective decidua and its spreading over wide area for proper nourishment makes the placenta membranous and intrude into lower segment.
- Big surface area of placenta.
Who are at high-risk of developing placenta previa?
- Multiparity
- Maternal age more than 35 years
- Asia women are at high risk of developing placenta previa and among them women of Manland China has the highest prevalence of placenta previa.
- Previous history of cesarean section, myomectomy, hysterotomy
- Prior curettage and placenta previa
- Multiple pregnancy
- Smoking, use of cocaine
Pathological changes in placenta and umbilical cord
Large and thin placenta with extensive areas of degeneration with calcification and infarction. Placenta may be morbidly adherent to lower segment.
Attachment of umbilical cord may be at margin or into the membranes and the insertion may be close to internal os.
Types of placenta previa
Type 1: Low-lying placenta previa
Only small part of placenta encroaches towards the lower segment but doesn’t reach the internal os.
Type 2: Marginal placenta previa
The placenta does not cover internal os but reaches the margin of it.
Type 3: Incomplete or partial central placenta previa
The placenta covers the internal os partially.
Type 4: Central or complete placenta previa
The placntacompletely overs the internal os even after os is fully dilated.
Newer way to differentiate placenta previa
Minor cases of placenta previa:
Placenta lying in lower uterine segment and the lower edge does not covers the internal os.
Major cases of placenta previa:
Placenta lying in lower uterine segment and covering the internal os.
How does Placenta Previa presents?
Vaginal bleeding is the only symptom of placenta previa which is of sudden onset, painless, apparently causeless and recurrent. Bleeding usually occurs at night and awakening the patient in a pool a blood and majority occurs before 38 weeks.
What findings are seen in Placenta Previa?
- The size of uterus is as that of usual period of gestation, and it is relaxed, soft and elastic without any localized tenderness.
- Increase incidence of malpresentation and multiple pregnancy.
- Head is not fixed and usually floating and cannot be pushed down into the pelvis.
- Fetal heart sound is usually present.
- Bright red or dark colored blood is seen on vulval inspection.
- Vaginal examination is avoided.
What investigations are done in this case ?
- Ultrasonography: It is the investiogation of choice. It can be transabdominal, transvaginal, transperineal.
- Three-dimensional power Doppler is the best.
- MRI
What are the other condition confused with Placenta Previa?
- Abruptio placenta
- Cervical polyp, carcinoma
Complications
| Maternal | Fetal |
| Antepartum hemorrhage | Fetal growth retardation |
| Early rupture of membrane | Low birth weight |
| Cord prolapse | Asphyxia |
| Intrapasrtum and postpartum hemorrhage | Birth injuries |
| Retained placenta | Intrauterine death |
| Sepsis | Congenital malformation |
| Embolism | |
| Subinvolution |
Management:
Management of placenta previa not only include treatment but also prevention to minimize the risk.
Prevention:
- Regular antenatal check-up and early confirmation of diagnosis.
Management at home:
- Patient is put to bed and proper assessment of blood loss.
- Gentle examination of abdomen to assess height of uterus and assess fetal heart sound.
- Avoid vaginal examination.
- Arrangement should be made to transfer patient to hospital well equipped with facility of blood transfusion, cesarean section, and proper neonatal case with intensive unit.
Hospital admission
- All cases of antepartum hemorrhage should be admitted to hospital.
Treatment at hospital
- First patient should be assessed for amount of blood loss.
- A large-bore IV canula is opened and blood is sent for blood grouping, cross-matching and hemoglobin estimation.
- Infusion of normal saline.
- Gentle examination of abdomen and vulval examination is done.
- Diagnosis is made.
Expectant management :
Macaffee regime:
Carry pregnancy till term for fetal lung maturation without putting mother at risk.
It should be continued until 37 weeks, but can be terminated immediately if patient rebleeds.
Indications:
- No active bleeding
- Patient is hemodynamically stable
- Period of gestation is less than 37 weeks
- Reactive cardiotocography
- Absent of fetal anomalies
Active management:
To terminate pregnancy irrespective of period of gestation.
Indications:
- Hemodynamically unstable and active bleeding
- Gestational age more than 37 weeks and in labor
- Fetal distress
- Fetal anomalies present
Mode of delivery :
It depends on types of placenta previa.
- Minor degree of placenta previa ( Type 1 and type 2 anterior ): Vaginal delivery is tried.
- Dangerous variety ( Type 2 posterior ): Cesarean section is done.
- Major degree (Type 3 or type 4 ): Cesarean section is done.
Prognosis
- In developed countries, maternal death is decreased to less tha 1% or even to zero in some centers.
- In developing countries, maternal mortality in hospital statistics is as high as 5%.
- Perinatal mortality ranges from 10% to 25%.
References:
- DC Dutta’s Textbook of OBSTETRICS; 9th Edition
- William’s Obstetrics 24th Edition
- https://www.ncbi.nlm.nih.gov/books/NBK539818/
- https://pubmed.ncbi.nlm.nih.gov/23551357/
- https://www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg27/
- Karami, M., & Jenabi, E. (2017). Placenta previa after prior abortion: a meta-analysis. Biomedical Research and Therapy, 4(07), 1441-1450. https://doi.org/10.15419/bmrat.v4i07.197
