Placenta Previa

Placenta previa occurs when the placenta extends into the vagina, potentially blocking the baby from emerging fully or partially during delivery.

Last Updated: February 21, 2024

In the third trimester, placenta previa affects 0.3–2% of pregnancies, and its prevalence has grown as cesarean section rates have risen.

The cause of placenta previa is unknown. However, endometrial (interior of the uterus) injury is linked to uterine scarring. Placenta previa risk factors include maternal age above 35, previous pregnancies, smoking, cocaine use, previous suction and curettage, ART, past cesarean section(s), and previous pregnancies.

Most of the time, placenta previa manifests as:

  • Bright red vaginal bleeding. Most of the time, the bleeding starts in the second half of the pregnancy. Additionally, it may begin, stop, and then resume a few days later. Lastly, bleeding can be caused by sexual activity, vaginal exams, or labor, but sometimes there is no clear reason;
  • Mild pain or cramping in the back, belly, or abdomen;
  • Vaginal bleeding might vary and is not always painful.

Doctors use ultrasound to view a female’s reproductive organs to diagnose placenta previa.

Vaginal ultrasonography (also known as transvaginal ultrasound) is a diagnostic procedure in which a wand-like instrument (a transducer) is inserted into the vagina to examine the uterus, placenta, and cervix.

Another way of detecting placenta previa is by abdominal ultrasound. A doctor will rub gel into your abdomen and maneuver a small handheld equipment (the transducer) in a circular motion around the outside of the belly. The placement of the placenta and cervix, as well as the developing infant, can be visualized in this way.

In both instances, the ultrasound images are displayed on a screen or monitor. From the images seen on the screen, doctors assess how much of the cervix is covered by the placenta.

In cases of posterior placenta previa or when evaluating the risk of bladder invasion, magnetic resonance imaging (MRI) is a useful diagnostic tool. However, it is expensive and has not been proven to improve diagnosis or outcomes over ultrasonography alone.

Treatment

Many women with early placenta previa recover on their own. As the uterus expands, the cervix may move farther from the placenta. The placenta may develop higher in the uterus and the margins near the cervix may decrease.

 

If placenta previa resolves, vaginal delivery may be possible. If not, a C-section is the preferred procedure.

When a woman has vaginal bleeding after 20 weeks, it is considered an emergency. If the mother is 36 weeks pregnant, the baby will probably be taken out by C-section. If she is losing a lot of blood or there is a risk to the mother or the baby's health, the mother may need an emergency C-section before 36 weeks.

When there is no bleeding, the goal of treatment is to lower the chance that the mother will bleed and get her as close to her due date as possible. Practices to avoid are the following to prevent bleeding:

  • Sexual encounters or sexual activities that could lead to orgasm
  • Moderate or strenuous exercise
  • Heavy or moderate lifting
  • Standing for long hours

It is impossible to avoid placenta previa, and no medical or surgical procedure can fix it. There is a way to reduce the chance of placenta previa by eliminating lifestyle choices including smoking and cocaine use. Once a doctor has made a diagnosis, it is necessary to take steps to lessen the bleeding.

References

Anderson-Bagga FM, Sze A. Placenta Previa. [Updated 2022 Jun 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK539818/

Cleveland Clinic (2022). Placenta Previa. Retrieved November 16, 2022, from https://my.clevelandclinic.org/health/diseases/24211-placenta-previa

Mayo Clinic (2022). Placenta Previa. Retrieved November 16, 2022, from https://www.mayoclinic.org/diseases-conditions/placenta-previa/diagnosis-treatment/drc-20352773

Last Updated: February 21, 2024