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Placenta Previa

Placenta previa is defined as an abnormal placentation near or covering the internal cervical os.


The only presentation of placenta praevia is vaginal bleeding [6]. Classical presentation of this bleeding is an unexpected one, with no pain and no apparent cause. These episodes can be recurrent.

In 5% of women, it occurs first time during labour especially in primigravidae. The bleeding is not accompanied by pain unless labour sets in simultaneously. Bleeding can occur after sexual intercourse. The first episode of bleeding is not heavy but subsequent bouts of bleeding will be heavier than the previous due to separation of fresh areas of placenta.

In most cases, bleeding occurs before 38 weeks. Asymptomatic cases may be detected on ultrasound or at the time of Caesarean section. Uterine contractions may be experienced.

Wound Infection
  • Perioperative complications included surgical wound infections (n   5), bladder injury (n   4), pelvic abscess (n   1), and uterine rupture (n   1).[ncbi.nlm.nih.gov]
Buttock Pain
  • Complications such as fever, buttock pain, or acute limb ischemia were not observed. The procedure was performed after partial cystectomy for two patients with bladder invasion.[ncbi.nlm.nih.gov]
Third Trimester Bleeding
  • American College of Radiology (ACR) Appropriateness Criteria for second and third trimester bleeding. Available at: . Updated 2013. Accessed June 6, 2016. Pregnancy complications. Office on Women's Health website. Available at: .[winchesterhospital.org]
  • About 20% of third trimester bleeding may be attributed to placenta previa[ 5]. Nearly all cases of placenta previa are delivered by cesarean section.[perinatology.com]
  • The bleeding often starts near the end of the second trimester or beginning of the third trimester. Bleeding may be severe and life threatening. It may stop on its own but can start again days or weeks later.[medlineplus.gov]
Second Trimester Bleeding
  • Pregnancies complicated with placenta previa had significantly higher rates of second-trimester bleeding (OR 156.0, 95% CI 87.2-277.5), pathological presentations (OR 7.6, 95% CI 5.7-10.1), abruptio placentae (OR 13.1, 95% CI 8.2-20.7), congenital malformations[ncbi.nlm.nih.gov]
  • Poor maternal outcomes include increased rates of peripartum hysterectomy, second trimester bleeding, maternal blood transfusion, maternal sepsis, vasa previa, malpresentation, and postpartum hemorrhage.[4] Poor neonatal outcomes include increased mortality[tamingthesru.com]
Placental Disorder
  • Abstract Placental disorders such as placenta previa, placenta accreta, and vasa previa are all associated with vaginal bleeding in the second half of pregnancy.[ncbi.nlm.nih.gov]
Vaginal Bleeding
  • Cervical varicose veins rupture should be considered for painless vaginal bleeding during the third trimester pregnancy.[ncbi.nlm.nih.gov]
Uterine Hemorrhage
  • Occasionally, women with placenta previa experience uterine hemorrhages that could potentially be fatal.[wikihow.com]
  • Nine patients were followed-up and the menstrual cycles of seven returned to normal in one month, one in two months, and one suffered amenorrhea.[ncbi.nlm.nih.gov]


A single episode of bleeding especially any time after the 20th week should be clinically examined and evaluated carefully.
Placenta praevia can be confirmed by both a thorough clinical examination and a good ultrasound which may be abdominal or transvaginal.

On clinical examination, the general condition and anaemia are proportionate to blood loss. Abdominal examination will reveal the size of uterus which is proportionate to the period of gestation. The uterus feels relaxed and soft without any localised areas of tenderness. Malpresentation is very common. The fetal head is floating in contrast to period of gestation. Fetal heart sounds are usually heard unless there is a major separation of the placenta.

Vulva is inspected to note whether bleeding is still present and to assess the amount of blood loss. Bleeding is bright red. Vaginal examination should not be done outside the operation theatre even in hospitals as it can stimulate further bleeding.

Ultrasound provides the simplest and most precise diagnosis. It can show the exact degree of placental involvement in relation to the internal os. Ultrasound assesses fetal size and status and normally confirms the diagnosis [7].

Transvaginal ultrasonography is also done as it is more accurate than transabdominal ultrasound, but the transducer should not touch the cervix.

MRI is an imaging technique which is patient friendly and gives very good placental images thus helping in an accurate diagnosis [8].


The treatment adopted will be decided after a complete clinical evaluation. If the bleeding is minimal with no distress to both mother and fetus and the duration of pregnancy is less than 37 weeks then bed rest is advised along with periodic examination of vulval pads and fetal wellbeing with USG at interval of 2-3 weeks.

Supplementary iron tablets should be given. Sexual intercourse is not allowed. Total bed rest with minimum exertion restricted to the bathroom should be advised, this treatment is carried on till 37 weeks, by that time fetus is sufficiently mature. This treatment has to continue unless there is active brisk haemorrhage which is continuing, indicating that the fetus is dead or malformed.

Active treatment is advocated if bleeding occurs at or after 37 weeks, patient is in labour, bleeding is continuous or if patient is in an exsanguinated state.

Grade 3 and Grade 4 normally require a definite Caesarean section [9]. The mode of delivery depends upon the amount of bleeding. If the bleeding is minimal and there is no stress to both mother and fetus, a vaginal delivery can be attempted.

If the bleeding is heavy, hospitalisation may be required. Blood transfusion should be arranged in cases of severe bleeding. A planned Caesarean section should ideally be done after 36 weeks. Steroid medications may be given to to hasten the maturity of fetal lungs.

If bleeding does not stop and there is distress to fetus or mother, an immediate Caesarean section might be performed [10].


There is considerable reduction in maternal deaths in placenta praevia due to early diagnosis, prompt treatment, effective antibiotics and omission of internal examination outside the hospital.

Deaths have been reduced to less than 1%. In certain developing countries death can range to as high as 5%. This is mainly due to inadequate antenatal care, delay in diagnosis and road and transport difficulties which result in a poor outcome of this condition.

Maternal complications which can occur during pregnancy are premature labour, malpresentation and antepartum haemorrhage.

Fetal mortality and morbidity are also reduced due to liberal use of Caesarean section and improved neonatal facilities. Perinatal mortality ranges from 10-25% mainly due to complications which include low birth weight, asphyxia, congenital malformations, and intrauterine death and birth injuries.


The exact cause of implantation of placenta in the lower segment of the uterus is not known. A number of factors seem to play a role in the etiopathogenesis. Different theories have been postulated.

  • Dropping down theory: The fertilized ovum drops down and is implanted in the lower segment. Poor decidual reaction in upper segment maybe the cause. Wherever the embryo gets implanted, the placenta grows there.
  • Chorionic activity still persists in the decidua capsularis which results in development of capsular placenta which comes in contact with the lower segment.
  • A very large surface area of the placenta as in twins may encroach the lower segment.

Various other risk factors include:


About one third of cases of antepartum haemorrhage belong to placenta praevia. Out of all of the obstetric cases in a hospital, placenta praevia accounts for about 0.5-1%. 80% cases are found in women who have had many pregnancies [3]. Increased usage of family planning methods with limitation and spacing of birth, lowers the incidence of placenta praevia. Repeated Caesarean sections can cause placenta praevia [4].

Fetal and maternal mortality is about 3-4 times higher than a normal pregnancy.

Sex distribution
Age distribution


When the embryo gets attached in the caudal part of the uterus, the placenta also gets attached and starts to grow along with the pregnancy. The placenta may be large and thin. Extensive areas of degeneration, infarction and calcification may be evident. The placenta may be morbidly adherent due to poor decidual reaction in the lower segment. Due to increased vascularity, the lower uterine segment and cervix become soft and friable.

Four types of placenta praevia are known depending upon the extension of placenta to the lower segment:

  • Grade 1 (low lying): A major part of the placenta is attached to the upper segment and only the lower portion encroaches into the lower segment but not up to the os.
  • Grade 2 (marginal): The placenta reaches the margin of the internal os but does not cover it.
  • Grade3 (incomplete or partial central): The internal os is partially blocked by the placenta.
  • Grade 4 (central or total): The placenta completely covers the internal os even after it is fully dilated.

In majority of the cases, the placenta lies either on the anterior or posterior wall, the latter is more common. Grade 3 and 4 constitute majority of the cases [5].

As the placental growth slows down in later months and lower uterine segment dilates and expands, the inelastic placenta is sheared off the wall. This leads to rupturing of utero-placental vessels which lead to an episode of bleeding. Bleeding is inevitable as this is a natural response. This separation can also occur in response to trauma, coital act, and even during internal examination. The bleeding is always maternal bleeding.


As placenta praevia is an inherent obstetric hazard with unknown cause, many steps can be taken to minimize the risks. Good antenatal care should be taken to improve health status. Thorough antenatal checkups should be done.

Antenatal diagnosis of low lying placenta at 20 weeks with repeated ultrasound at 34 weeks should be done to confirm diagnosis. Any episode of bleeding should not be ignored and should be reported to the medical examiner immediately. Family planning methods should be adopted to prevent multiple pregnancies.


Placenta praevia is an obstetric condition in which the placenta gets implanted partially or completely over the lower uterine segment. This is the commonest cause of antepartum hemorrhage.

It occurs in the second and third trimester of pregnancy which usually results in bleeding into the genital tract. Placenta is the organ through which the unborn baby gets nourishment from the mother, so as the pregnancy continues, the uterus expands and stretches and so does the placenta. By the last three months of the pregnancy, the placenta should reach the upper part of the uterus.

In certain pregnancies, the placenta still lies low in the uterus and either totally or partially occludes the cervix of the uterus. This leads to severe bleeding which can occur before or during labour.
If detected early in pregnancy, it does not pose a problem, but if it still persists in later months of pregnancy it can lead to severe complications which can affect both mother and baby [1].

Patient Information

Placenta praevia is a condition which results in vaginal bleeding before or during delivery. It occurs when the placenta gets attached to the lower segment of the uterus thereby blocking the opening of the birth canal. This results in easy and frequent bleeding. This can happen any time after 24 weeks of pregnancy.

In some cases, the placenta moves upwards away from the birth canal as the pregnancy progresses and settles down, but in certain cases the placenta does not. These cases have to be handled with care as bleeding can happen anytime.

The exact cause is not known but there are many risk factors including multiple pregnancies, smoking, increased maternal age and infertility treatments. The typical symptom is painless, bright red bleeding which occurs normally between 20 to 32 weeks of pregnancy.

Any episode of bleeding must not be taken lightly and ignored, but brought to the attention of the physican. The physician will do a complete physical examination and repeated ultrasounds will be done to assess the extent of placenta blocking the birth canal.

Depending upon the severity the physician will decide the plan of treatment. For cases with little or no bleeding, complete bed rest with regular check-up is recommended. Vaginal delivery can be attempted, but normally Caesarean sections are done after 37 weeks when baby is mature enough.

If there is severe bleeding immediate hospitalisation with complete rest will be advised. Emergency Caesarean section has to be carried out incase there is any stress to mother or baby.
Family planning methods should be adopted along with birth spacing should be done to prevent this condition. With proper care and regular follow up placenta praevia can be managed well.



  1. Zlatnik MG, Cheng YW, Norton ME, Thiet MP, Caughey AB. Placenta previa and the risk of preterm delivery. J Matern Fetal Neonatal Med. 2007 Oct;20(10):719-23.
  2. Creasy RK, Resnik R, IamsJ , Lockwood C, Moore T. Placenta previa and abruptio placentae. In: Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice: Expert Consult. 6th ed. WB Saunders: Philadelphia, Pa; 2008:725-29.
  3. Marshall NE, Fu R, Guise JM. Impact of multiple cesarean deliveries on maternal morbidity: a systematic review. Am J Obstet Gynecol. 2011 Sep;205(3):262.e1-8.
  4. Milosevic J, Lilic V, Tasic M, Radovic-Janosevic D, et al. [Placental complications after a previous cesarean section]. Med Pregl. 2009 May-Jun;62(5-6):212-6.
  5. Ghi T, Contro E, Martina T, Piva M, et al. Cervical length and risk of antepartum bleeding in women with complete placenta previa. Ultrasound. Obstet Gynecol. 2009 Feb;33(2):209-12.
  6. Oppenheimer L. Diagnosis and management of placenta previa. J Obstet Gynaecol Can. 2007 Mar;29(3):261-73.
  7. Gagnon R, Morin L, Bly S, Butt K, et al. Guidelines for the management of vasa previa. J Obstet Gynaecol Can. 2009 Aug;31(8):748-60.
  8. Allen BC, Leyendecker JR. Placental evaluation with magnetic resonance. Radiol Clin North Am. 2013 Nov;51(6):955-66.
  9. Vergani P, Ornaghi S, Pozzi I, Beretta P, et al. Placenta previa: distance to internal os and mode of delivery. Am J Obstet Gynecol. 2009 Sep;201(3):266.e1-5.
  10. Machado LS. Emergency peripartum hysterectomy: Incidence, indications, risk factors and outcome. N Am J Med Sci. 2011 Aug;3(8):358-61.

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Last updated: 2019-06-28 12:21