Recognising 5 Common Placental Conditions in Clinical Practice

A healthy placenta plays a vital role in pregnancy and fetal development, yet modern obstetric care is seeing a rise in placenta issues, some associated with an upswing in cesarean deliveries.

Although many placenta issues in pregnancy remain relatively rare — preeclampsia being a notable exception — more patients may be vulnerable today than in past decades. Understanding common risk factors, coupled with careful ultrasonographic evaluation, can inform clinical decision-making when diagnosing and managing these five common placental issues in pregnancy.

1. Preeclampsia

Preeclampsia appears in up to 8 percent of pregnancies globally, reports a 2020 practice bulletin from the American College of Obstetricians and Gynecologists (ACOG), posing a grave danger to both the carrying parent and the baby.

Although the syndrome's root cause remains debatable, Circulation points to a body of clinical and pathological research suggesting a central role for the placenta in preeclampsia. Preeclampsia is known for its sudden progression, making gathering important clinical information crucial.

To aid in a prompt diagnosis, the Society for Maternal-Fetal Medicine (SMFM) identifies the following serious risk factors:

- Past diagnosis of preeclampsia

- Chronic hypertension

- Multiple gestations

- Type 1 or 2 diabetes mellitus

- Autoimmune disease

Clinical diagnosis includes findings of new-onset high blood pressure and organ dysfunction. Evaluating your patient's risk at their first prenatal visit proves helpful in assessing their vulnerability and, as warranted, suggesting preventive measures.

A joint committee opinion from ACOG and SMFM recommends a low dose of aspirin daily for high-risk patients or those with two or more moderate risk factors. Three separate studies find that starting at-risk patients on low doses of aspirin beginning in the second trimester lowers preeclampsia risks by one-quarter.

2. Placenta Previa

Among the rare placenta issues during pregnancy, placenta previa occurs when the placenta partially or entirely blocks the cervical os. The condition affects an estimated 1 in 200 pregnancies, reports Obstetrics & Gynecology, with rates varying globally.

Placenta previa is a chief risk factor for postpartum hemorrhage, making the condition dangerous and potentially deadly to some mothers. Preterm birth is also a concern.

Although the underlying cause of the condition remains elusive, its incidence appears to be linked to rising numbers of cesarean deliveries. A retrospective cohort study in Obstetrics & Gynecology finds higher rates of previa among women with a cesarean first birth than those with a vaginal first birth. Additional risk factors include:

- Previous miscarriage or termination

- Previous uterine surgery

- Advanced maternal age

- Multiple gestations

- Smoking

Symptoms include painless vaginal bleeding in the second or third trimester, but patients may also report contractions, abdominal pain or both. Routine transabdominal ultrasonography screening is the first step to systematically evaluating the placental location. When placenta previa is suspected, transvaginal ultrasonography may inform clinical decision-making by more accurately determining the distance between the placenta and os.

Cesarean delivery is the universally preferred treatment, reports Obstetrics & Gynecology. For patients wishing to attempt a vaginal delivery, papers in BJOG and the Journal of Ultrasound in Medicine suggest that a trial labor may be appropriate among patients with a distance of 2 cm or greater between the placenta and os.

3. Placental Abruption

Placental abruption happens when the placenta prematurely detaches from the uterine wall, generally sometime after 20 weeks of gestation, depriving the developing fetus of essential oxygen and nutrients. Highly dangerous but rare, abruption appears in just 1 percent of pregnancies in the U.S., and remains a leading cause of bleeding in later pregnancy, reports Obstetrics & Gynecology.

A 2017 systematic review in the American Journal of Perinatology further links the condition with postpartum bleeding, preterm birth, low birth weight and perinatal death in severe cases. Pregnant patients may experience sepsis, amniotic fluid embolism, venous thromboembolism, acute kidney injury and other harms. Newborns may go on to develop encephalopathy, severe respiratory disorders, acidosis, acute kidney injury, chronic lung disease or epilepsy.

As with placenta previa, medical literature finds a consistent association between past cesarean delivery and placental abruption. Obstetrics & Gynecology reports that individuals with two consecutive cesarean deliveries were 30 percent more likely to experience abruption in their third pregnancy than those who'd delivered vaginally. Other at-risk patients include those with:

- Previous abruption

- Advanced maternal age

- Preeclampsia

- Multiple gestations

- High blood pressure

- Trauma

- Smoking/cocaine use

As to environmental factors, emerging research in the American Journal of Epidemiology finds higher rates of abruption among patients exposed to nitrogen dioxide in the first trimester and fine particulate matter in the third trimester.

A review in Obstetrics & Gynecology advises tailoring delivery options to your patient, depending on the severity of the abruption and fetal gestational age. Making vaginal delivery a goal may be feasible for those who are near term when abruption occurs, with a healthy fetus in stable condition. However, prompt cesarean delivery is advisable when the health of the parent or fetus appears in jeopardy.

4. Placenta Accreta Spectrum

A spectrum disorder, placenta accreta involves differing degrees of unhealthy attachment by the placenta. Related conditions include placenta increta, where the placenta invades uterine muscles, and placenta percreta, where the placenta penetrates the uterine wall. Although largely symptomless, placenta accreta may develop in tandem with placenta previa, thus causing vaginal bleeding as a warning sign. Without careful management, the condition may trigger potentially deadly hemorrhaging at delivery.

Similar to placental abruption, reports in the U.S. confirm rising rates of placenta accreta, appearing in 1 in 300 pregnancies, far outpacing historical rates — and likely tied to higher cesarean rates in the modern era. Indeed, a previous cesarean delivery is the chief risk factor for the condition, concludes the latest joint committee opinion from ACOG and SMFM, with the risk increasing with successive cesarean deliveries.

Apart from a history of cesarean childbirth, vulnerable patients also include those with:

- Asherman syndrome

- Two previous births

- Past uterine surgeries

Although the origin of this disorder isn't fully understood, theories suggest a defect of the endometrial–myometrial interface, affecting the development of uterine scar tissue. Yet, as a joint committee opinion from ACOG and SMFM observes, this theory fails to explain the rare instances where pregnant individuals with no history of uterine surgery and no previous deliveries go on to develop placenta accreta.

Diagnosis begins with obstetric ultrasound, which can detect features of accreta as early as the first trimester, although most cases are diagnosed later in pregnancy. For patients without symptoms, current guidance advises ultrasound exams at approximately 18–20 weeks, 28–30 weeks and 32–34 weeks gestation.

Delivery with placenta accreta calls for thoughtful counselling and careful planning to protect the health of the parent and baby. ACOG and SMFM note that co-management by the patient's obstetrician in consultation with a level III or IV care facility may provide them with a reassuring continuity of care while minimizing the time spent away from home and family.

5. Placental Insufficiency

As the name suggests, placental insufficiency occurs when a smaller-than-normal or poorly functioning placenta restricts the supply of oxygen and nutrients to the growing fetus. The condition may worsen over time, leading to fetal hypoxemia, intrauterine growth restriction, preterm birth and stillbirth in some cases. Maternal-Fetal and Neonatal Endocrinology notes that approximately 8 percent of pregnancies are complicated by placental insufficiency leading to intrauterine growth restriction, which also may be referred to as fetal growth restriction.

In medical literature, the term placental insufficiency may appear interchangeably with poor placental function. Notably, the European Journal of Obstetrics & Gynecology and Reproductive Biology points out the lack of a standardized definition or consensus around what constitutes placental insufficiency, potentially standing in the way of advances in clinical understanding and management.

In terms of risk factors, studies confirm a linkage between placental insufficiency and preeclampsia. Certain medical and lifestyle issues also may elevate risk, as the condition is more commonly seen in those with:

- Diabetes

- Clotting disorders

- Smoking/drug use

For diagnosis, StatPearls advises regular prenatal Doppler ultrasound screening to assess fetal and placental circulation, thus aiding in early detection. When MRI evaluation is available, Magnetic Resonance in Medical Sciences finds an association between placental insufficiency and MRI measures of placental volume, thickness, area, flow void size and placenta-to-amniotic-fluid signal intensity ratio.

Although treatment is generally limited to delivery when the fetus reaches viability, early research suggests that low doses of aspirin and vitamins C and E may assist in promoting successful placentation.