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Everyone knows children inherit some things from their parents: their blue eyes, their curly hair, or perhaps their love of the outdoors. Moms take prenatal vitamins and get maternal vaccines like Tdap to transfer health benefits and good antibodies to their unborn babies. 

But some maternal antibodies carry risks that pregnant women should understand. Though serious dangers are rare, expectant mothers should be aware of them and prepared to discuss them with their doctors as part of their prenatal care.

When Mom’s Immune System Fights Baby’s Blood Cells

When a baby’s blood type is incompatible with his or her mother’s, sometimes mom’s immune system sends antibodies to “fight” the baby’s red blood cells. This rare condition, known as hemolytic disease of the fetus and newborn, affects between 3 and 80 pregnancies per 100,000, usually during the second or subsequent pregnancies.

Severe symptoms, while extremely rare, once took the lives of thousands of infants every year. Medical progress has greatly reduced that number. Hemolytic disease of the fetus and newborn is treatable today with fetal blood transfusions.

When Baby Inherits Incompatible Blood Cells from Dad

Another rare disease stemming from blood-cell incompatibility occurs when a baby inherits blood platelets from his or her father. When this happens, mom’s immune system may respond to her baby’s unfamiliar platelets as if they were attacking her, sending harmful antibodies into the womb and giving the child fetal and neonatal alloimmune thrombocytopenia.

To date there is no national screening for either blood cell-type incompatibility condition or test to predict their severity. The most common indicator is a sibling who already has it. So doctors should closely monitor expectant mothers during subsequent pregnancies, and prepare for delivery and neonatal care accordingly.

When Mom Has Certain Autoimmune Diseases

Sometimes harmful antibodies transferred to unborn babies have nothing to do with compatibility, but instead result from their mothers’ own immune systems. This is the case with congenital heart block. When a woman with an autoimmune condition like lupus or Sjogren’s syndrome gets pregnant, her body may create antibodies that attack her child’s heart as it develops in the womb.

Congenital heart block is very rare, affecting one in every 15,000-20,000 births. It is also becoming easier to diagnose, thanks to ongoing advances in medical imaging technology. Current treatments include certain medications and insertion of a pacemaker in the baby’s heart after the baby is born.

These conditions can happen, even if an expectant mom follows every prenatal protocol, which is why new, better and less invasive treatments are needed. The good news is that scientists are working to develop better tests and treatments – for all of these as well as other rare, fetal and infant conditions.

Doctors know what to look for and to test for these conditions, as necessary. Women should know and ask about them, too, so they can better advocate for themselves and their children.

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