The role of the placenta during pregnancy

The role of the placenta during pregnancy

The placenta and its health are vital to the health of a woman’s pregnancy and foetal development. This organ provides oxygen, nutrients during pregnancy, and filters foetal waste.

It also plays an important role in hormone production and it protects the foetus from bacteria and infections. The blood-rich placenta is joined to the uterine wall and connects to the baby by way of the umbilical cord. Most often, the placenta attaches itself to the top or side of the uterine wall. At times, however, it may grow or attach to the uterus in a way that can cause health problems.

Risk factors for placental disorders

Many factors influence the health of the placenta, including:

  • Ethnicity
  • History of smoking cigarettes
  • High blood pressure
  • Multiple gestation pregnancy
  • Maternal blood-clotting disorders
  • History of uterine surgery such as a caesarean delivery
  • History of placental problems
  • Maternal substance abuse, such as cocaine use
  • Abdominal trauma, such as from a fall or blunt trauma
  • Maternal age – women over the age of 40 area at a higher risk for developing placental problems
  • Premature rupture of membranes – the risk of placental problems increases when the amniotic sac ruptures prematurely.

There are many complications that can affect the placenta. The most common disorders are discussed below.

Placenta Previa is a condition in which the placenta attaches to the wall of the uterus very low down. In doing so, the placenta partially or completely covers the cervix.

This condition occurs in 0.5% to 1% of pregnancies. The condition may resolve as the pregnancy progresses, however.

Placenta previa is most common in women who are:

  • Of minority races
  • Older
  • Smokers
  • Have a history of abortion, caesarean delivery or other uterine surgery
  • Carrying a multiple gestation pregnancy.

There are two types of placenta previa: marginal and complete.

Marginal placenta previa is when the placenta only partially covers the cervix.

Complete placenta previa fully covers the cervix. Placenta previa can cause vaginal bleeding both before and during birth. This bleeding can be severe at times.

Placenta previa can cause the following complications during pregnancy:

  • Placental tear
  • Increased risk for foetal infection
  • Bleeding
  • Contractions
  • Preterm labour.

Most often, a caesarean delivery will be required to deliver the baby safely.

Placental abruption occurs when the placenta separates from the uterus during pregnancy. Abruption can be either partial or complete.

High blood pressure can raise the risk of placental abruption.

The condition occurs most commonly in the third trimester. It is the most common placental disorder and occurs in up to 1 out of every 100 pregnancies.

Placental abruption is the leading cause of foetal and newborn death. It also causes high rates of premature delivery and foetal growth restriction.

The risk of placental abruption can be increased by:

  • Trauma to the abdomen
  • Premature membrane rupture
  • Smoking
  • Use of cocaine
  • History of a prior placental abruption
  • Defects of the uterus
  • Maternal high blood pressure or pregnancy-induced high blood pressure
  • Circumvallate placenta.

Expectant mothers with placental abruption may experience vaginal bleeding, uterine or abdominal pain, continuous contractions, and foetal heart rate abnormalities.

A diagnosis of placental abruption will be based on symptoms, and treated according to their severity.

Due to the role that the placenta plays in oxygen and nutrient delivery, placental abruption can cause deprivation of these vital nutrients.

This deprivation can lead to abnormal foetal development, premature delivery, foetal growth restriction, and stillbirth.

As previously discussed, the placenta plays a vital role in foetal development by providing a growing baby with nutrients and oxygen and filtering their waste products. At times, however, the placenta may not function properly. When this happens, it can fail to deliver adequate quantities of nutrition, causing placental insufficiency.

This placental abnormality will often result in foetal growth restriction and a low birth weight in infants. Women with placental insufficiency may notice less foetal movement and a smaller uterus size than before. There can be both maternal and foetal consequences related to placental insufficiency. Maternal risks increase in the presence of diabetes and high blood pressure.

Many expectant mothers experience symptoms of placental insufficiency such as:

  • Placental abruption (see above)
  • Preterm labour and delivery
  • Preeclampsia

Preeclampsia is characterized by high blood pressure and the presence of protein in the urine. Symptoms of preeclampsia include excessive weight gain, oedema, headaches, and high blood pressure.

Foetal and infant risks in the presence of placental insufficiency include:

The presence of placental insufficiency early in pregnancy worsens the problems that are experienced by the baby. While there is no cure for placental insufficiency, receiving recommended follow-up and prenatal care is vital.

Healthcare providers may evaluate your pregnancy regularly by recommending:

  • More frequent office exams
  • Kick count records
  • Education on self-monitoring for symptoms of preeclampsia
  • Bed rest
  • Steroid injections before 32 weeks if preterm labour is a risk
  • Evaluation with high-risk maternal foetal medicine specialists.

In severe cases, expectant mothers may require an inpatient hospital stay.

Placental infarcts are areas of dead tissue found within the placenta, typically caused by blood vessel complications.

This placental abnormality decreases blood flow to the affected areas, which at times can cause foetal growth restriction or death. Placental infarcts are more commonly experienced by women with severe high blood pressure.

Having a caesarean section could increase the risk of placenta accreta in the future. Placenta accreta is a condition that occurs in 1 in 2,500 pregnancies. The placenta and its blood vessels attach and grow deeply into the wall of the uterus. This serious medical condition has three forms:

  • Placenta accreta: the placenta is attached to the uterine wall muscle
  • Placenta increta: the placenta is attached through the uterine wall muscle
  • Placenta percreta: the placenta grows through the entire uterine wall and attaches to other surrounding organs.

Risk factors for developing placenta accreta are mainly unknown but are thought to include a history of placenta previa and previous caesarean sections. Complications of this condition can include third trimester vaginal bleeding, severe postpartum haemorrhage, caesarean delivery, and subsequent hysterectomy.

If worried that any of these conditions may apply to you or your pregnancy, or for any further information, we recommend that you contact your healthcare provider.