The placenta in pregnancy

The placenta is the supply chain and waste disposal for the baby in your womb. After studying a few second-trimester and hundreds of third-trimester placentas from women with Covid-19, researchers determined the virus causes significant destruction within this vital organ.
The placenta is the supply chain and waste disposal for the baby in your womb. After studying a few second-trimester and hundreds of third-trimester placentas from women with Covid-19, researchers determined the virus causes significant destruction within this vital organ.

Covid-19 is a highly infectious disease caused by a strain of the coronavirus. This strain is named the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), although commonly referred to as Covid-19. It chiefly affects the respiratory system, causing pneumonia and difficulty breathing. Covid-19 is likely to be severe if you get it during pregnancy, more so during the third trimester. Recent research has found how Covid-19 infection affects the placenta.

Women with Covid-19 have a much higher risk of adverse fetal outcomes than those without infection. Knowing how Covid-19 affects the placenta helps in understanding the outcomes.

The placenta is the supply chain and waste disposal for the baby in your womb. It supplies oxygen, glucose, and other nutrients a growing baby needs. It also serves to remove carbon dioxide and other waste products. Structures within the placenta called the chorionic villi are essential for exchanging blood between maternal and fetal circulations.

The placenta attaches to the wall of your uterus and connects to your baby by the umbilical cord. Your baby is dependent on the placenta for growth and survival. 

The placenta's work extends beyond blood and nutrient supply and waste disposal. It makes and releases hormones that affect pregnancy, metabolism, baby growth, and labor. The placenta also protects your baby from infections and harmful chemical substances by acting as a filter.

With so many crucial functions in pregnancy, it's easy to see why any disease affecting the placenta harms the pregnancy and baby. 

Pregnancy outcomes with Covid-19 

Pregnancy is a vulnerable time. Your body makes many changes to physiology, circulation, and the immune system to accommodate your growing baby.  

Covid-19 can be harmful at any stage of pregnancy. Its effects are most severe during the third trimester of pregnancy when your Covid-19 infection is more likely severe. Covid-19 in the third trimester puts babies at risk too. There are higher chances of premature delivery and stillbirth (death of a baby in the womb). 

While certain viruses can cross the placenta, infect the baby, and cause birth abnormalities, like the varicella-zoster virus, cytomegalovirus (CMV), and Zika virus, there are no increases in the rates of birth abnormalities in babies born to women with Covid-19 during pregnancy. Researchers believe that the placenta prevents the Covid-19 virus from crossing it and causing infection in the baby since most babies born to positive mothers do not have the infection.

Covid-19 infection and the placenta

The SARS-CoV-2 virus attaches to cells with angiotensin-converting enzyme 2 (ACE2) receptors on their surface. Cells of the respiratory system are rich in ACE2 receptors, which explains why most symptoms of Covid-19, including cough, sore throat, and breathing difficulty, are respiratory symptoms.

The placenta also has ACE2 receptors. The virus attaches to these and enters the placental cells. Not all women with Covid-19 have a placental infection. Of these, very few pass on the virus to their babies.

After studying a few second-trimester and hundreds of third-trimester placentas from women with Covid-19, researchers determined the virus causes significant destruction within this vital organ, including the following:

Deposition of fibrin. Fibrin is a blood protein that enhances clot formation. Fibrin deposits around 20% or more of placental terminal villi may reduce the transfer of substances between mother and baby, causing fetal growth restriction.

Infarction. The death of a part of the organ is usually because of a blocked blood supply. Covid-19 causes clotting in the blood vessels. Many cells dying in a part of the placenta reduce its functional capacity.

Vasculopathy. The walls of the blood vessels are damaged. Damaged walls form clots, cutting off blood supply to a part of the placenta.

Inflammation. Immune cells like macrophages are present in large numbers in the placenta. They likely migrate there to neutralize the virus. The resulting inflammation includes villitis, intervillositis, fetal vasculitis, and chorioamnionitis. 

All these changes, individually or in combination, reduce the ability of the placenta to function. The fetal blood circulation that is crucial for the baby's survival and growth is disturbed, a condition called fetal vascular malperfusion (FVM). The baby doesn't get oxygen and nutrition in adequate amounts, and wastes also build up. The resulting outcomes are fetal growth restriction, miscarriage, premature delivery, and fetal death.

A small proportion of babies born to women with Covid-19 have SARS-CoV-2 at birth. These babies likely have the infection from the mother through the placenta (vertical transmission), although this is still unclear. On examining the placentas, virus particles are present on the fetal side, in cells of the chorionic villus stroma or the trophoblast. There is significant inflammation, indicating infection on the fetal side of the placenta.

Indirect effects of Covid-19 on the placenta

Pregnancy is an unfortunate time to get Covid-19. Because of your body's physiological and immunological changes, the infection is likely to progress to severe disease. You have an increased risk of hospitalization, needing intensive care, and mortality.

Severe Covid-19 pneumonia causes hypoxia, a lowering of the oxygen content of your blood and affecting the entire body since all cells in the body need oxygen. Low oxygen levels in the blood cause reduced blood flow to some organs, including the uterus. A period of low blood flow and reduced oxygen supply injures the placenta.

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Conclusion

Covid-19, when severe, causes widespread destruction in the body. There is no way to predict how much damage the virus will do once you get infected. If you get Covid-19 during pregnancy, your placenta may be affected, putting your baby at risk. Take precautions and talk to your doctor about vaccinations to keep you and your baby safe.

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Medically Reviewed on 4/6/2022
References
SOURCES:

Centers for Disease Control and Prevention: "Pregnant and Recently Pregnant People."

Diagnostics (Basel): "The Effects of COVID-19 on Placenta and Pregnancy: What Do We Know So Far?"

Frontiers in Immunology: "The Effects of COVID-19 on the Placenta During Pregnancy."

Morbidity and Mortality Weekly Record: "Risk for Stillbirth Among Women With and Without COVID-19 at Delivery Hospitalization."

Thrombosis Research: "Growth and function of the normal human placenta."

Viruses: "Placental Pathology of COVID-19 with and without Fetal and Neonatal Infection: Trophoblast Necrosis and Chronic Histiocytic Intervillositis as Risk Factors for Transplacental Transmission of SARS-CoV-2."