Читать книгу You: Having a Baby: The Owner’s Manual to a Happy and Healthy Pregnancy - Michael Roizen F. - Страница 41

Positives and negatives aren’t just important for jump-starting a car battery; they’re also important for determining whether a baby has blood compatibility with mom. This comes in the form of something called the Rh factor—a chemical tag that differentiates blood types. You’re classified as Rh-positive if you have the factor on red blood cells and negative if you don’t. The tricky part happens if mom is negative and dad is positive: If the child gets dad’s type (which is likely, as Rh-positive is a genetically dominant trait), and Rh-positive cells leak into mom’s bloodstream as the placenta breaks down during delivery, then her body responds by producing antibodies that fight the positive antigens. Because there is no blood-to-blood contact during pregnancy, Rh disease is rare in a first pregnancy. But once mom’s antibodies have been activated, they will freely cross the placenta into the fetus’s bloodstream during subsequent pregnancies and tag the baby’s red blood cells for destruction, causing anemia or other serious conditions.

This situation can be prevented by giving an Rh-negative mother a prophylactic injection of an Rh immunoglobulin called RhoGam, which prevents the antibodies from forming, either midway during her first pregnancy or within seventy-two hours after delivery if it is known that the father is Rh-positive. In situations where the father’s blood type is unknown, it’s best for an Rh-negative woman to get the injection anyway to decrease the risk of this problem occurring. In circumstances where the mother suffers a miscarriage or has an ectopic pregnancy, it’s common practice to give her the injection within seventy-two hours if she is Rh-negative, to avert the chances of her forming antibodies due to lack of information about the father’s blood type in an emergency situation. Rh tests are given during prenatal visits to help ID potential problems.

body shifts from rebel mode^* to ally mode, as it nurtures, feeds, and makes peace with what it should perceive as a foreign invader: the fetus.

Remember that 50 percent of the fetus’s genes are from the father and theoretically