Placenta previa is a condition in which the placenta (including
the marginal veins of the placenta) partially or completely covers the opening of the cervix (cervical os).
The placental edge covers the internal cervical os. Follow-up
ultrasonography is recommended at 32 weeks of gestation.
Low lying placenta
The placental edge is less than 2 cm from the internal os but not covering
the internal os. Follow-up ultrasonography is recommended at 32 weeks of
LifeART images © 2006
Lippincott Williams & Wilkins. All rights reserved.
In 2014 the Executive Summary of a Joint Eunice Kennedy Shriver National
Institute of Child Health and Human Development, Society for Maternal-Fetal
Medicine, American Institute of Ultrasound in Medicine, American College of
Obstetricians and Gynecologists, American College of Radiology, Society for
Pediatric Radiology, and Society of Radiologists in Ultrasound Fetal Imaging
Workshop recommended eliminating the terms partial and marginal and only
retaining the terms placenta previa and low-lying placenta.
Placenta previa occurs in one in 200 to 250 births overall,
but is much more common if a woman has given birth before, has had a cesarean
section, has had placenta previa with a previous pregnancy, or is over the age
of 35. It is uncommon in nulliparous women (women who have never given birth)
The main symptom of placenta previa is vaginal
bleeding. The bleeding is typically painless unless there is coexisting
abruption or labor. About 20% of third trimester bleeding may be attributed to
placenta previa[ 5].
Nearly all cases of placenta previa are delivered by cesarean section.
Infrequently patients with marginal previa and minimal bleeding are allowed to
deliver vaginally as are patients with intrauterine fetal demise (stillbirth) or
a previable pregnancy.
1.Becker RH et al., ,The relevance of placental location at 20-23 gestational weeks
for prediction of placenta previa at delivery: evaluation of 8650 cases.
Ultrasound Obstet Gynecol. 2001 ;17(6):496-501.
2.Mustafá SA, et al,Transvaginal ultrasonography in predicting placenta previa at
delivery: a longitudinal study.Ultrasound Obstet Gynecol. 2002 ;20(4):356-9.
3.Dashe JS, et al. Persistence of placenta previa according to gestational age at
ultrasound detection. Obstet Gynecol. 2002;99:692-7.
4. Reddy UM, etr. al. Fetal imaging: executive summary of a joint eunice kennedy
shriver national institute of child health and human development, society for
maternal-fetal medicine, american institute of ultrasound in medicine, american
college of obstetricians and gynecologists, american college of radiology,
society for pediatric radiology, and society of radiologists in ultrasound fetal
imaging workshop. J Ultrasound Med. 2014 May;33(5):745-57.
5. Benedetti TJ Obstetric hemorrhage in
Gabbe ed: Obstetrics - Normal and Problem Pregnancies, 4th ed New York, NY,
Churchill Livingstone; 2002
Reviewed: Mark Curran, M.D.