Placenta | Invasive Placenta
Invasive placenta refers to a condition in which the placenta attaches too strongly or invades too deeply into the wall of the uterus. This may result in the placenta not separating and delivering as it usually does following delivery of the baby, and may cause extra bleeding if efforts to remove the placenta are made. The disease can be categorized by severity:
- Placenta accreta: the placenta attaches too strongly to the muscular layer of the uterine wall (the myometrium), but does not invade it
- Placenta increta: the placenta invades into the myometrium
- Placenta percreta: the placenta invades through the full thickness of the uterine wall, and can attach to adjacent organs in the abdomen, usually the bladder
Many scientific publications use the term placenta accreta to refer to all types and circumstances of invasive placentation. However, the patchy disease and the variable location of the placenta, together with a variable number and type of risk factors meaning that every patient is different. Recently, we published an overview of multi-disciplinary approach to management of invasive placenta and its impact on maternal well-being and pregnancy outcome (see abstract).
Normally, the placenta attaches to the outer layer of the uterus (decidua). The placenta must be strong enough to anchor to this layer until the end of pregnancy, but must detach immediately after delivery.
The decidua is very important in achieving this balance because it controls the depth of invasion of the placenta and orchestrates the ability of the placenta to release when the baby is delivered. Therefore, if the decidua is damaged or abnormal, an invasive placenta may develop. This is most commonly seen in the area of a scar on the uterine wall from a previous Caesarean section or other uterine surgery.
Any history of damage to the decidua may increase your risk of an invasive placenta. This includes:
- Previous Caesarean section is the biggest risk factor for invasive placenta. The risk of future invasive placenta progressively increases with the number of Caesarean deliveries (although the vast majority of women who have Caesarean sections do NOT develop invasive placentas in subsequent pregnancies). The reason for this increased risk is that the Caesarean section always leaves a scar on the internal surface of the uterus. The internal surface (endometrium) may be thin at this scar area, which is in the lower part of the front wall of the uterus, but this does not cause any problems between pregnancies. However, in a subsequent pregnancy, this scar area may become the site of invasive placentation. It is not known why some women develop invasive placentas at scar sites, while most do not.
- Women who have had one or more Caesarean sections are therefore at risk of invasive placenta in any pregnancy where the placenta is low-lying across the previous uterine scar site on the lower front of the uterus (anterior placenta previa). If the ultrasound locates the placenta to be in the normal position (in the fundus [top] of the uterus), or on the posterior wall (back wall), then the risk of invasive placenta is lower.
- A special type of Caesarean called a classical Caesarean section is sometimes performed in complicated pregnancies. This classical Caesarean section has a higher risk of invasive placenta in subsequent pregnancies, because it is a vertical incision up the middle of the uterus. In such women, it is more likely in another pregnancy that the placenta will implant across the scar, because the placenta usually implants higher up in the uterus (in the fundus).
- Previous gynecological uterine surgeries such as myomectomy (removal of a fibroid) and one or more D&C’s
- D&C means a dilation (of the cervix) and curettage (removal of tissue from the uterus). D&C may be performed for menstrual problems or after pregnancy due to persistent vaginal bleeding from retained placental fragments. D&C may increase the risk of a future invasive placenta, again because of scarring of the decidua. D&C is an important operation which, in many circumstances, restores health, and the vast majority of women who have an uncomplicated D&C do not have an invasive placenta in subsequent pregnancies. However, women who have had a difficult D&C, or multiple D&C’s, may be at risk of invasive placenta.
- Intra-uterine surgery: a minor surgery can be performed via the opening the cervix (hysteroscopic surgery) and may create scarring of the non-pregnant endometrium. However, sometimes the surgery is performed in women with pre-existing endometrial defects. The risk of an invasive placenta should be considered in the following circumstances:
- Surgery for Asherman syndrome
- Hysteroscopy myomectomy (removing a polyp does not affect the endometrium)
- Hysteroscopy to resect (remove) a septum in the uterus (“infertility surgery”)
- Embolization treatment for a fibroid (in place of myomectomy surgery)
- Note: If you are considering embolization treatment for one or more fibroids and wish to have children in the future, you should discuss the risk of invasive placenta with your doctor. You may wish to defer this treatment option until you have completed your reproductive career.
- Embolization for fibroids uses tiny (250µM) polyvinyl (plastic) micro-beads that are floated into the feeding vessel of the fibroid. These cannot be digested so they permanently reduce blood flow locally in and around the fibroid.
- It is important to note that other types of embolization do exist, including embolization for post-partum hemorrhage. In contrast to embolization for fibroids, embolization for post-partum hemorrhage uses substances that can be naturally-digested, and thus does not increase the risk of an invasive placenta in subsequent pregnancies.
Symptoms and signs
There are no symptoms or signs of an abnormally-adherent placenta. The diagnosis of invasive placenta may not be made until attempts are made to remove the placenta after delivery of the baby. Because these attempts may cause extra bleeding, it is ideal if the diagnosis is made antenatally (during the pregnancy), so that specific preparations can be made for delivery in these cases.
If a patient has risk factors for invasive placentation (see below), an ultrasound and MRI can be used to help diagnose invasive placenta.
The diagnosis of invasive placenta can be strongly suspected by ultrasound if the texture of the placenta and its border with the muscle of the uterus are seen to be abnormal.
An MRI scan is the best test to confirm the ultrasound findings in those patients who have an abnormal placental appearance suggesting an invasive placenta. The ultrasound and MRI findings may be very obvious, or may be difficult to differentiate from normal. Therefore, an evaluation by personnel who are experienced with these issues is recommended.
If a diagnosis of invasive placenta is made or suspected, we at the Placenta Clinic suggest the following plan:
- Antenatal evaluation by a team experienced in the diagnosis of invasive placenta, using ultrasound and MRI;
- If this evaluation confirms the presence of an invasive placenta, subsequent care and management of the patient is best conducted by a team experienced with the surgical challenges of this diagnosis;
- This team is comprised of caregivers from a number of different areas, including: obstetrics, vascular and interventional radiology (VIR), gynaecological surgery, anaesthesiology, hematology, diagnostic imaging, and pathology;
- For each individual patient and her family, a care plan should be developed which incorporates her previous medical and obstetrical history, the results from the ultrasound and MRI, the patient’s home address (proximity to a major hospital), and her future pregnancy wishes. This care plan would involve the following:
- Planned Caesarean delivery in a specialized unit;
- May include planned hysterectomy in severe cases;
- Extra IVs and catheters during the time of the surgery (see next paragraph on vascular and interventional radiology).
A key component of care in women with suspected invasive placenta is access to vascular and interventional radiology (VIR). This type of doctor is a radiologist with additional training in placing catheters inside blood vessels for the purpose of blocking off vessels that are bleeding. VIR is an integral part of the assessment and management of women with suspected invasive placenta.
We have published on this topic, as below:
- Our first successful case employing the strategy of conservative management of invasive placenta, by performing a Caesarean section that deliberately leaves the placenta inside the uterus to slowly dissolve over several months (see abstract by Dr. Alkazaleh, published in the Journal of Obstetrics and Gynaecology Canada, August 2004);
- Review of our experience of the conservative management of 10 subsequent patients (see abstract by Dr. Amsalem, published in the Journal of Obstetrics and Gynaecology Canada, October 2011).
Role of placental function testing
Although maternal biochemistry is more frequently found to be abnormal in patients with invasive placenta, compared with the general pregnant population, these findings cannot be used as a diagnostic test at present. Placental ultrasound is essential in establishing the diagnosis of invasive placenta; the ultrasound focuses on the border between the placenta and the wall of the uterus, and the texture of the placenta. Uterine artery Doppler has no utility in the diagnosis of invasive placenta.
Many women with a diagnosis of invasive placenta will require hysterectomy at the time of Caesarean section and will have VIR performed, and some women may require blood transfusions. The most significant complication of the invasive placenta is bladder injury at the time of surgery requiring repair.
However, overall, if the diagnosis of invasive placenta has been made antenatally, our experience has been that women should recover extremely well with no long-lasting complications.
In order for the Caesarean to be performed in a controlled fashion, it is usually scheduled a number of weeks before full term. However, the babies usually require very little extra help and are expected to develop normally and healthily following a brief stay in the nursery.
In those patients who do not have a hysterectomy at the time of their Caesarean section, we always carefully discuss future pregnancy plans and contraception. Published research indicates that the rate of recurrence is high following a previous pregnancy with an invasive placenta.