Placenta Previa Symptoms and Causes: A Complete Medical Guide for Expecting Mothers

Placenta previa is a pregnancy complication where the placenta attaches to the lower part of the uterine wall, partially or totally covering the cervix—the opening to the birth canal. It is a primary cause of antepartum haemorrhage, which refers to vaginal bleeding occurring after 20 weeks of gestation. While the condition requires specialized clinical monitoring, early diagnosis and modern obstetric care allow most women to have a safe and healthy delivery.

Knowing the specific types and causes of low placenta during pregnancy, and recognizing early warning signs, can help you navigate this condition with confidence.

Types of Placenta Previa: Understanding the Classification

Obstetricians classify placenta previa into four distinct grades based on the proximity of the placental edge to the internal cervical os (the internal opening of the cervix):

• Grade 1 (Low-Lying Placenta): The placenta is implanted in the lower uterine segment, but its edge does not reach the internal cervical os. In approximately 90% of cases diagnosed in the second trimester, the placenta will naturally move upward as the uterus expands.
• Grade 2 (Marginal Placenta Previa): The edge of the placenta reaches the margin of the internal cervical os but does not cover it.
• Grade 3 (Partial Placenta Previa): The placenta partially covers the internal cervical os. This typically necessitates a Cesarean section (C-section) to prevent life-threatening bleeding during labor.
• Grade 4 (Total or Complete Placenta Previa): The placenta completely covers the internal cervical os. This is the most clinically significant form and strictly requires a planned C-section.

From the Expert’s Note- Symptoms of Pregnancy Week by Week

Symptoms of Placenta Previa

Primary Symptoms and Antepartum Haemorrhage

The hallmark sign of placenta previa is painless, bright red vaginal bleeding during the second or third trimester. This is a leading contributor to antepartum haemorrhage, and because it is often painless, it can occur suddenly without warning.

This bleeding occurs because the lower uterine segment thins and the cervix begins to efface (thin out) or dilate in preparation for birth, causing the placental attachments in that area to shear and bleed.

Other Potential Symptoms

While painless bleeding is the classic presentation, some patients may experience:

• Mild cramping or uterine contractions associated with the bleeding.
• The baby being in an unusual position, such as breech (feet down) or transverse (lying sideways), because the placenta is occupying the space the head would normally take in the lower pelvis.
• Signs of premature labour, including pelvic pressure or regular backaches.

If you notice any vaginal bleeding or a significant change in fetal movement, it is imperative to contact your obstetrician immediately for an evaluation.

How is Placenta Previa Diagnosed?

Most cases are identified during a routine 20-week anatomy scan. If placenta previa is suspected, your healthcare provider will use the following diagnostic methods:

• Transabdominal Ultrasound: A standard non-invasive scan to view the placental position.
• Transvaginal Ultrasound: Regarded as the "gold standard" for diagnosis, this provides the most accurate measurement of the distance between the placental edge and the cervix.
• MRI (Magnetic Resonance Imaging): Utilized occasionally if there is a suspicion of placenta accreta spectrum (where the placenta attaches too deeply into the uterine wall), a condition more common in patients with repeat C-sections.

Learn More about Types of High-Risk Pregnancies and Their Management

Causes of Low Placenta During Pregnancy

Factors That Increase the Risk

While the exact reason a placenta implants in the lower segment is not always clear, several factors increase the likelihood of developing placenta previa:

• Previous Uterine Surgery: Scars from a previous C-section, D&C (dilation and curettage), or fibroid removal (myomectomy) can affect where the placenta attaches.
• Multiple Gestation: Carrying twins or triplets requires a larger placental surface area, increasing the chance of it encroaching on the cervix.
• Maternal Age: Women aged 35 or older have a higher statistical risk of placenta previa.
• Previous Placenta Previa: The risk of recurrence in a subsequent pregnancy is estimated at 2% to 3%.

Other Contributing Factors

• Smoking and Substance Use: Smoking during pregnancy increases the risk of placental complications by causing hypoxemia, which may lead to placental hypertrophy (enlargement) as the body tries to compensate for reduced oxygen.
• Uterine Abnormalities: An unusually shaped uterus or the presence of large fibroids can limit the space available for high implantation.

Understanding Delivery Options: Vaginal or C-Section

Management and "Pelvic Rest"

If you are diagnosed with a low placenta during pregnancy, the primary goal is to manage the risk of bleeding and reach a safe gestational age for delivery.

One of the most critical recommendations is "Pelvic Rest," which includes:

• Strictly avoiding sexual intercourse (as cervical stimulation can trigger bleeding).
• Avoid the use of tampons or douching.
• Restricting heavy lifting and strenuous physical activity.

In cases of significant antepartum haemorrhage, hospitalization may be necessary to monitor the mother’s hemoglobin levels and the baby’s heart rate. In some instances, corticosteroids are administered to accelerate the baby’s lung development if an early delivery is anticipated.

Conclusion

Placenta previa is a manageable condition when detected early through regular prenatal screenings. While the term may seem daunting, the majority of women with a low-lying placenta go on to have healthy pregnancies and successful deliveries with the right medical guidance. If you experience any symptoms, such as painless bleeding, do not hesitate to seek clinical advice. At Nanavati Max Super Speciality Hospital, our team of experts is dedicated to providing the highest standard of maternal-fetal care to ensure the safety of both you and your baby.

Medical Disclaimer: The information provided in this article is for educational purposes only and does not substitute professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or a qualified healthcare provider regarding a medical condition. 

Frequently Asked Questions

1. What does the bleeding from placenta previa look like? 

It is typically bright red and occurs without pain. This form of antepartum haemorrhage can range from light spotting to heavy flow and requires immediate medical evaluation.

2. Can placenta previa cause severe pain? 

Usually, no. The bleeding is characteristically painless. If severe pain is present, it may indicate other complications such as placental abruption, where the placenta separates prematurely from the uterus.

3. What increases the risk of placenta previa in pregnancy? 

Key factors include previous C-sections, maternal age over 35, smoking, and carrying multiple babies (twins/triplets).

4. Can a low placenta "move" up? 

Yes. Through a process called "placental migration," as the lower part of the uterus grows and stretches, the placenta often moves away from the cervix. This occurs in about 90% of cases diagnosed early in pregnancy.

5. What is the safest delivery method? 

If the placenta continues to cover the cervix (Total or Partial Previa) in the third trimester, a planned C-section is the only safe delivery method to prevent severe haemorrhage.

References

1. Silver, R. M. (2015). Abnormal Placentation: Placenta Previa, Vasa Previa, and Placenta Accreta. Obstetrics & Gynecology, 126(3), 654–668.
https://doi.org/10.1097/AOG.0000000000001005

2. Royal College of Obstetricians and Gynaecologists (RCOG). (2018). Placenta Praevia and Placenta Accreta: Diagnosis and Management (Green-top Guideline No. 27a).

https://www.rcog.org.uk/guidance/browse-all-guidance/green-top-guidelines/placenta-praevia-and-placenta-accreta-diagnosis-and-management-green-top-guideline-no-27a/