Placenta Previa: Causes, Symptoms and Diagnosis

Placenta previa is amongst the more important complications of the second and third trimesters in obstetrics. The condition is quite unnerving to expectant mothers and families alike. This blog is all about what placenta previa is, types of placenta previa, how it is diagnosed and managed, and how the delivery plan is undertaken if present.

What is Placenta Previa?

The placenta is normally implanted high up in the upper uterine segment, far away from the cervical os. Placenta previa involves an abnormal implantation of the placenta low down in the uterus and it covers all or part of the internal os. The reason why this is a serious issue is that during delivery the cervix needs to dilate, but this cannot happen if the placenta blocks it since the lower segment distends and the cervix effaces. This condition complicates about 0.3-0.5% of pregnancies at term. Detected early, the placenta may shift due to growth of the uterus, while later on special management of placenta previa and delivery are needed.

Types of Placenta Previa

Complete (total) previa:

The placenta completely covers the internal os. Vaginal delivery is not possible. Caesarean section is necessary.

Partial Placenta Previa:

Here, the placenta extends to cover the internal os of the cervix partially. Obstetrical management depends on the degree of coverage, and Caesarean section is often required.

Marginal Placenta Previa:

The edge of the placenta extends to the margin of the internal os but does not extend beyond it. Depending on the distance, vaginal delivery can be attempted in selective cases after ultrasound measurement.

Low-Lying Placenta:

The edge of the placenta is less than 2 cm from the internal os but does not cover it. There is increased risk associated with this condition compared to low-lying placenta.

What are the Placenta Previa grades?

Placenta previa is categorized according to the proximity of the placenta to the cervix. It is usually categorized in the following ways:

Grade 1 (Low Lying Placenta):

The placenta is located at the lower uterine segment but does not cover the internal cervical os.

Grade 2 (Marginal Placenta Previa):

The margin of the placenta reaches the internal cervical os but does not obstruct it.

Grade 3 (Partial Placenta Previa):

The placenta partially covers the internal cervical os and makes it difficult for vaginal birth to take place.

Grade 4 (Complete Placenta Previa):

The placenta entirely covers the internal cervical os and necessitates a Cesarean birth.

Symptoms of Placenta Previa in Pregnancy

Placenta previa signs and symptoms is painless vaginal bleeding. Other placenta previa symptoms include:

Sudden and bright red bleeding from the vagina, without any apparent reason

Bleeding that starts, stops, and recurs again

Soft and non-tender uterus on examination

Fetal malposition.

Some women do not bleed at all, and their condition is diagnosed through ultrasounds.

Presence of no symptoms does not diminish the clinical importance of this finding.

Placenta Previa Causes & Risk Factors

Some of the common causes and risk factors include the following:

Previous caesarean delivery; increased risk with every subsequent scar on the uterus

Previous history of any form of uterine surgery including myomectomy, D&C and endometrial ablation

Age > 35 years

Multiparity

Multiple pregnancy (twin or multiple pregnancies); large surface area of placenta

Smoking (placental hypertrophy and implantation abnormalities)

In-vitro fertilization (increased risk with ART conception)

History of previous placenta previa increases the risk of recurrence.

Placenta Previa Diagnosis

Regular anomaly scans from 18 to 20 weeks detect most cases.

Transabdominal ultrasound scan: Helpful screening test but not accurate

Transvaginal ultrasound (TVS): This is the diagnostic test and offers more accurate assessment of placental edge-to-os distance compared to transabdominal scanning.

MRI: Done if there is suspicion of placenta accreta spectrum (abnormal growth) together with placenta previa, especially in women with previous uterine scar

If previa is detected during anomaly scans, repeat TVS scan at 32 and 36 weeks can be done to find out if placental edge moves away from os to reassess mode of delivery.

Treatment for Placenta Previa

No treatment can reposition the placenta. Placenta Previa Treatments involves ensuring the health of mother and baby until baby is old enough to be delivered safely.

Pelvic rest: No coitus, no vaginal examination, and no transvaginal manipulations unless clinically indicated.

Activity restriction: Not all women are put on bed rest, but activity restriction is advised especially in those who bleed.

Hospital admission: Those with active bleeding, women living far away from tertiary centers, and women with complete placenta previa who enter their third trimester.

Corticosteroids: Either Betamethasone or Dexamethasone between 24 and 34 weeks to hasten fetal lung maturity in case of early delivery.

Transfusion of blood: In case of heavy bleeding, especially with anemic mothers, to maintain hemodynamic stability and fetal oxygenation.

Tocolysis: Temporary use of uterine relaxants in case of contractions along with active bleeding.

Risks/Complications to Mother and Child

The common complications are:

Antepartum haemorrhage - recurrent episodes increase the possibility of progressive maternal anaemia.

Postpartum haemorrhage - contraction of the lower uterine segment is poor postpartum and this leads to excessive blood loss

Placenta accreta spectrum - especially in women with previous Caesarean scars, the placenta can be invasive into myometrium or deeper; it is the most dangerous complication and may need hysterectomy

Premature delivery - nearly all symptomatic women with previa deliver before 37 weeks

Intrauterine growth retardation - the position of the placenta in the lower segment may lead to compromised perfusion

Malpresentation - breech/transverse presentation makes the delivery difficult.

Delivery Planning with Placenta Previa

Full previa and partial previa are definite indications for a Caesarean section, scheduled in uncomplicated cases at 36-37 weeks; recurrent bleeding necessitates an earlier delivery. The operating surgeon cross-matches blood in advance and expects considerable blood loss during the procedure. If the possibility of accreta spectrum on MRI is present, a multidisciplinary approach is organised pre-operatively involving interventional radiology, urology, and vascular surgery. Prophylactic balloon catheterisation or ureteric stenting can be done prior to the incision by skilled centres.

Does Placenta Previa Resolve by Itself?

During the first trimester of pregnancy, most cases of low placentation turn out to be normal as the uterine body grows. This causes the formation of a larger lower uterine segment, thus resulting in a relatively more elevated location of the placental edge. Full previa identified at the anomaly scan resolves in some patients, while marginal previa found early on has a greater chance of resolution. Placenta previa which persists beyond 32 weeks is highly unlikely to resolve adequately for vaginal delivery.

Also Read: Anterior vs Posterior Placenta: Understanding Placental Position During Pregnancy

Precaution and Lifestyle during pregnancy

For women suffering from placenta previa, some advice includes:

Visit for all planned ultrasounds, especially those around week 32 and 36, where TVS will be very conclusive

Adhere to pelvic rest measures such as abstinence from sexual intercourse and internal exams

Be aware of the symptoms, including vaginal bleeding, that need urgent medical attention irrespective of the amount

Remain close to a tertiary obstetric hospital after week 28 if there is complete previa

Ensure your iron intake – haemoglobin concentration of more than 10 g/dL is an adequate safeguard against sudden blood loss

Do not strain yourself as the Valsalva maneuver can trigger bleeding

Consider making plans for delivery early on and remember that having a planned cesarean operation relieves your stress.

Conclusion

Placenta previa is a condition that should be diagnosed and managed in time to avoid complications for the woman and the child. If you have symptoms like vaginal bleeding without pain during pregnancy, do not ignore them. With today's developments in prenatal care and management of high-risk pregnancy, almost all patients with placenta previa have successful deliveries under proper medical supervision.

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Also Read: Posterior Placenta: Meaning, Types, and Its Impact on Pregnancy

Frequently Asked Questions

1. What is placenta previa, and how common is placenta previa?

Placenta previa is the condition where the placenta attaches itself to the lower uterine segment, obstructing the cervix either partially or wholly. It makes vaginal delivery impossible, poses the risk of haemorrhage, and demands special handling by the obstetrician from diagnosis up to delivery.

2. What are the symptoms of placenta previa?

Painless, bright red vaginal bleeding during the second or third trimester. There will be no tenderness of the uterus, which distinguishes placenta previa from placental abruption. Some patients never have any symptoms, and this condition is detected via routine ultrasound.

3. What causes placenta previa?

It is caused by the improper attachment of the placenta in the lower uterine segment. Uterine scars following Caesarean delivery, D&C, or myomectomy are the predisposing factors that have been identified.

4. How is Placenta Previa diagnosed?

Placenta previa can be diagnosed with the help of transvaginal ultrasonography. Transvaginal ultrasonography is relatively more accurate than a transabdominal sonogram. This disease can be identified through the 18-20 weeks anomaly scan and the 32 and 36 weeks rescan. If placenta accreta is suspected, MRI is done.