The placenta is a structure that develops together with your baby inside the uterus during pregnancy. It plays the important role of passing on oxygen and nutrients from you to your baby. It is delivered shortly after the baby is born which is referred to as the third stage of labour, hence the placenta is also called “the afterbirth.”
Placental attachment is of critical importance during pregnancy. It attaches to the wall of your uterus, usually at the top or the side. This placement allows enough space for the baby to grow.
However, it’s not always like that for some expectant moms. There are cases where the placenta attaches low in the uterus where it ends up covering part or all of the cervix, which is the entrance of the womb.
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Complications arise when the placenta is positioned low in the uterus or is covering the cervix. This condition is generally called Placenta Praevia, and it must be carefully monitored because any form of obstruction impairs normal vaginal birth. It also increases your risk for severe bleeding during your pregnancy and delivery.
Normally, the placenta moves upwards and out of the way as the uterus grows in the next nine months. However, for some women, the placenta persistently takes root on the lower part of the uterus as the pregnancy progresses. It is classified into three types based on how it is positioned in relation to the cervical opening, which you can see in the image below.
It is worth noting that when observed in early pregnancy, what may be seen could be a false impression of a low-lying placenta. The placenta may simply be compressed towards the lower part of the uterus due to an overdistended bladder, which is intentionally done so for an abdominal ultrasound.
Therefore, not all initial diagnosis of placenta previa will progress into the late stages of pregnancy. For some, the expansion of the uterus will cause the placenta to go with it, moving up and away from the cervix. This is referred to as “placental migration”. However, it doesn’t mean that the placenta detaches, the term is only used to describe the positional changes of the lower placental edge towards the upper portion of the uterus, away from the cervical opening. Because of this, most cases of low lying placenta diagnosed at the 20 week fetal anomaly scan resolve by the third trimester.
What causes Placenta Praevia?
There are several factors that have been identified to cause placenta praevia. In the first place, it can happen when a fertilised egg (embryo) implants dangerously low in the uterus. As shown above, it may form close to or directly over the cervical opening.
Sometimes, issues in the uterus itself can also cause the problem. Abnormalities in the lining of the uterus (endometrium), such as fibroids or scarring from a previous C-section, surgical procedures like repeated currettage, or placenta previa, can potentially result in another one. An abnormally shaped uterus or placenta can also be contributing factors.
The chances are doubled in women who are pregnant with multiples (e.g. twins, triplets). Furthermore, a mother who has had several pregnancies also has a higher risk. Meanwhile, those who are over the age of 30 have a risk that is three times higher compared to those under 20.
External factors also come into play. For instance, a mother who smokes cigarettes or uses cocaine have a higher risk. Placenta praevia may also occur in pregnancies that have been conceived through assisted reproductive technology, such as IVF.
What are the symptoms of placenta praevia?
Placenta praevia where the placenta is overlying the cervix is often detected by ultrasound at around 20 weeks. The clinician would usually highlight this to the mother to monitor for vaginal bleeding in the second or third trimester. This type of bleeding is often painless and may occur after having sex hence abstainence from intercourse is advised for such patients. Some may also have accompanying contractions that can be felt like cramping or tightening.
However, not all women with placenta praevia have these symptoms. But even if you have no prior symptoms, there is still a small risk that you could bleed suddenly and heavily. In these cases, an emergency C-section may have to be done.
Why is placenta praevia a cause for concern?
The biggest risk in placenta praevia is bleeding during pregnancy, and excessive blood loss during and after delivery. This can be life threatening and rarely fatal to both you and your baby. This is especially if the placenta is not just low lying, but also adherent and growing into the uterine muscle wall preventing easy detachment after delivery. This much feared complication is called a placenta accreta and is associated with severe bleeding after delivery that may necessitate removal of the uterus. Therefore, it’s important to have the proper care available to you in this delicate pregnancy.
Typically, bleeding occurs during the third trimester of pregnancy when the lower part of the uterus thins out in preparation for labour. This causes the portion of the placenta which is over the cervix to bleed. Therefore, the more of the placenta that covers the cervical opening, the higher the risk for bleeding.
How is placenta praevia diagnosed?
Placenta praevia can be diagnosed through ultrasound during a routine prenatal check-up taken on the 20th week of pregnancy, or after an episode of vaginal bleeding. Most cases are diagnosed during a second trimester ultrasound exam. It can show the location of the placenta and how much of it is covering the cervix.
Meanwhile, a transvaginal ultrasound can help confirm a placenta praevia diagnosis. It is even considered to deliver a more accurate diagnosis. It’s a wand-like probe that is gently placed inside the vagina. This is carefully done by your doctor so that it is safe for both you and your baby.
A transvaginal ultrasound will also be helpful in monitoring placenta praevia since your OB will avoid routine vaginal exams to reduce the risk of heavy bleeding. Additional ultrasounds may be needed to check where your placenta is lying during your pregnancy, and to see if placenta previa resolves.
What is antenatal care like for placenta praevia?
Your plan of care will be unique because it will be based on factors unique to you and your baby. This will be determined by your doctor based on:
- Your overall health and medical history
- The health and gestational age of the baby
- The exact location of the placenta
- Extent of the condition (whether the placenta praevia is complete or partial)
- The position of the baby
- Whether you experience bleeding in pregnancy (ante partum hemorrhage).
No treatment can change the position of the placenta. Once a diagnosis is made, additional ultrasound scans are performed to track its location. Your cervix will also be measured at 32 weeks to check if there’s a chance that you will go into labour early, or check if you have an increased risk for bleeding.
Birth Plan for Placenta Previa Cases
If you are diagnosed with placenta praevia with minimal or no bleeding, pelvic/bed rest or hospital admission may be advised by your doctor. Bed rest will differ for each expectant mom, and it may range from simple periodic resting at home to full bed rest with monitoring in a hospital.
With this in mind, you will be able to plan things around your bed rest, and make the necessary arrangements at work and seek home assistance.
After 36 weeks, delivery of the baby may be a suitable treatment. Your doctor will first assess the risk of bleeding against early delivery of your baby. You may be offered a course of steroid injections between 34 and 36 weeks of pregnancy to help your unborn baby’s lungs to develop more quickly if it is likely that it will be a preterm earlier delivery. This is especially so for patients who have bleeding symptoms in the third trimester.
Most women with placenta previa will need a C-section. If your scan at 36 weeks shows that the edge of your placenta is less than 20mm from the entrance of the cervix, a C-section will be the safest way for you to give birth. If the placenta is further than 20mm from your cervix you may choose to have a vaginal birth. If you have heavy bleeding before your planned date of delivery, you may be advised to have your baby earlier than expected.
Severe blood loss may require blood transfusion. If personal reasons prevent you from getting it, you need to discuss this with your doctor and also note it in your birth plan.
If you know you have a low-lying placenta, you should contact the hospital straight away if you have any vaginal bleeding, contractions, or pain. Visit your OB or you can book a non-obligatory consultation with Dr Pamela Tan today.
Dr Pamela Tan is a board certified obstetrician and gynecologist in Singapore. She finished her undergraduate studies at the National University of Singapore and earned her post-graduate degree at the Royal College of Obstetricians and Gynaecologists in the UK. She is an accredited specialist by the Specialist Accreditation Board (Ministry of Health), and a fellow of the Academy of Medicine, Singapore. She subspecialises in colposcopy and is certified to perform Level 3 minimally invasive keyhole surgeries such as laparoscopic hysterectomy, myomectomy and cystectomy. Dr Pam also supports the natural birthing method and she strives to provide a personalised care and treatment for each patient.