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How does the mother's body know not to reject the fetus?

Dr. Michael Roizen, MD
Internal Medicine
The human body is designed to retaliate when a foreign matter invades it; that rebellion can come in the form of fevers, vomit, diarrhea, and the like, as your body finds ways to expel the bacteria, virus, or spoiled scallop. Yet in pregnancy, the mother's body shifts from rebel mode to ally mode, as it nurtures, feeds, and makes peace with what the body should perceive as a foreign invader—the fetus.

Remember that 50 percent of the fetus's genes are from the father and theoretically can carry information that could sabotage the relationship between mother and child. But the mother's immune system overlooks this fact and seeks to protect the child anyway. In a way, you can consider pregnancy an immuno-suppressed state; the volume of mom's immune system is turned down as it deals with this foreign, yet welcome, invader.

The most dangerous time for the newly created creature that is to become your child is prior to implantation in the uterine wall. If mom's immune system is not suppressed when the fertilized egg tries to land, it's bye-bye blastocyst. So exactly one day before implantation—six days after conception—the blastocyst produces a special enzyme that suppresses mom's killer T cells, preventing her from having an immune reaction against the baby-to-be's cells. Once the placenta is formed after implantation, it helps maintain the truce between these two potential adversaries.
YOU: Having a Baby: The Owner's Manual to a Happy and Healthy Pregnancy

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YOU: Having a Baby: The Owner's Manual to a Happy and Healthy Pregnancy

Can I get a cavity filled while pregnant? Will avoiding spicy foods make my kid a picky eater? Can I really increase my baby's IQ while she's in utero? Whether you're pregnant for the first time,...

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.