The maternal immune system undergoes profound and complex changes during pregnancy to support the developing fetus. These adaptations are natural and necessary, ensuring the success of the pregnancy, rather than simply becoming “weakened.”
How Pregnancy Affects Immunity
During pregnancy, the maternal immune system faces a unique challenge: tolerating the fetus, which carries paternal genetic material and is thus perceived as semi-foreign, while still protecting against infections. This delicate balance, called immune tolerance, prevents the mother’s immune system from rejecting the fetus, similar to an organ transplant.
The placenta plays a central role in mediating these immune interactions, acting as an immunological barrier. Failure to induce these systemic changes can lead to adverse pregnancy outcomes, such as preterm birth or preeclampsia.
Specific Immune System Changes
The balance of T helper cells shifts from a T helper 1 (Th1) dominant response to a T helper 2 (Th2) dominant response. Th1 cells promote cell-mediated immunity and inflammation, which could be detrimental to the fetus, while Th2 cells facilitate humoral immunity and tolerance. This Th2 shift helps suppress Th1-mediated inflammation and promotes tolerance to the fetus.
Regulatory T cells (Tregs), which have immunosuppressive properties, increase significantly during pregnancy, peaking in the second trimester. These cells are important for maintaining immune tolerance and preventing maternal immune responses against fetal antigens. Natural Killer (NK) cells, while abundant in the uterus during early pregnancy, are less cytotoxic than those in the peripheral blood and play a role in placental development and vascular remodeling. The overall aim of these cellular adjustments is to create an environment conducive to fetal growth while maintaining immune surveillance.
Practical Health Considerations
The immune adaptations during pregnancy, while essential for fetal development, can alter a pregnant individual’s susceptibility to certain infections. Pregnant individuals may experience increased risk or severity from infections like influenza, Listeria, and toxoplasmosis. Influenza, for example, can lead to more severe illness, hospitalization, and potential complications like preterm birth or low birth weight in pregnant individuals. Listeria infection, though rare, poses serious risks including miscarriage, stillbirth, or severe illness in the newborn. Toxoplasmosis, often mild in healthy individuals, can cause serious birth defects if acquired during pregnancy.
Given these considerations, maintaining health during pregnancy involves specific proactive measures. Vaccination against recommended diseases like influenza, tetanus, diphtheria, pertussis (Tdap), COVID-19, and Respiratory Syncytial Virus (RSV) is important and safe during pregnancy. These vaccines not only protect the pregnant individual but also transfer protective antibodies to the baby, providing early immunity.
Food safety practices are also important to prevent infections like Listeria and toxoplasmosis. This includes avoiding high-risk foods such as unpasteurized milk, soft cheeses, and deli meats unless heated to steaming. Thoroughly washing fruits and vegetables, cooking meats to safe temperatures, and practicing good hand hygiene, especially after handling raw meat or gardening, can help reduce the risk of toxoplasmosis.