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Though there are no true allergic reactions to a pregnancy itself, there are a number of conditions that can manifest as pregnancy allergies. These conditions may be caused by allergic reactions to certain pregnancy hormones or by an allergy-like response to the Rhesus (Rh) factor on a fetus’s red blood cells. The symptom of an allergic reaction to pregnancy caused by hormonal incompatibilities is usually persistent nausea. Reactions to an incompatible Rh factor may include jaundice, anemia, and brain damage in the fetus, sometimes leading to miscarriage. Other allergy symptoms such as hives, swelling, or rash, known as the pruritic urticarial papules and plaques of pregnancy (PUPPP) also occur during pregnancy
Hyperemesis gravidarum, a condition that is sometimes referred to by laymen as an allergic reaction to pregnancy, is a relatively uncommon condition that can be caused by sensitivity to a hormone known as human chorionic gonadotropin. The main symptoms of this allergy-like condition are severe nausea that won’t go away and frequent, often violent vomiting. In the past, this condition was severe enough that it caused the death of many women. Now, the use of intravenous fluids and the ability to administer nutrients make it possible for even severely ill women to give birth and recover.
The Rh blood factor can also cause symptoms similar to an allergy to pregnancy. The symptoms are only present when a mother with Rh- blood has been exposed to Rh+ blood, possibly from a previous pregnancy or a blood transfusion, and is carrying an Rh+ fetus. The primary symptoms for this disorder affect the unborn baby, as the mother’s body creates antibodies that attack and kill the baby’s red blood cells. The baby can develop a number of problems related to low blood count, including anemia, brain damage, cardiovascular damage, and death.
Another condition that could be considered an allergic reaction to pregnancy are PUPPP. The symptoms of this disorder are eczema, hives, swelling, and itchiness that can occur on the stomach and breasts or all over the body. The rash will often spread across the body and is blotchy and red in appearance. It is not known what causes this type of allergic reaction to pregnancy, though some theories suggest that it may be caused by an inflammatory response triggered by the rapid growth of the fetus or by the fetus’s deoxyribonucleic acid (DNA).