There are a variety of factors involved with what will happen to the immune system in pregnancy. Some studies show that a woman is more likely to have a lowered immune response during this time, and this can occur for a variety of reasons. How much, or even whether, a woman is affected will depend mainly on her lifestyle, health, and how strong her immune system was to begin with. Since each person reacts to pregnancy a little differently, there is no way to know precisely how one's body will respond.
One key factor changes in the immune system in pregnancy is hormones. There is a link between hormonal imbalance and a weakened immune system. It's also true that a woman's body is working hard to deliver nourishment to her developing baby, so other bodily systems often take a hit. This includes the immune system, especially in women who do not lead a healthy lifestyle. Eating immune-boosting foods and getting plenty of exercise may combat this.
Another factor which comes into play in regards to the immune system in pregnancy is the fatigue many women experience during the first and third trimesters. A lack of sleep can deplete immune function if it is prolonged, and pregnant women often experience insomnia at some point during their pregnancies. This can be caused by hormonal fluctuations, as well as by discomfort caused by morning sickness, stretching muscles and skin, and other pregnancy ills. Getting up throughout the night to urinate as the uterus pushes down on the bladder can also lead to a less restful sleep. To combat this, pregnant women should go to bed a little earlier, and take daily naps if able.
Some women may also have a weakened immune system in pregnancy because the growing baby is depleting her nutrient stores faster than she is replenishing them. A growing fetus requires a lot of nourishment during its nine months of development, and if the mother isn't eating enough of the right kinds of foods, the baby will get the nutrition it needs from the mother's nutrient stores. This leaves less nutrition for the mother's body to function properly, and this can lead to a sluggish immune system. To remedy this problem, all pregnant women should eat a balanced diet of whole grains, fruits, vegetables, lean proteins, and low-fat dairy. Pregnant women are encouraged to speak with their doctor about proper pregnancy nutrition, as some foods may be off limits.
Another issue that has been noted in regards to the immune system in pregnancy, is the fact that sometimes the mother's immune system may react negatively toward the growing baby. Most women's bodies have protective cells that work against this, but in some cases miscarriage can occur. It is also thought that pre-eclampsia could be caused by an immune response.