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“The Shot” PDF Print E-mail
Written by Laura Maxson, LM   

A pregnant woman might not know her exact blood type, but she’ll usually know if it’s the kind that needs “the shot.” Calling it “the shot” doesn’t really convey the amazing protection offered against Rh isoimmunization by the injection of Rho(D) Immune Globulin (RhIG), often referred to as RhoGAM®. (RhoGAM® is actually the brand-name of the first product developed to combat Rh isoimmuniztion). Until the 1960s many Rh negative mothers experienced sad outcomes to their pregnancies, either miscarriage or stillbirth, or babies born extremely ill, necessitating a complete blood transfusion for any chance at life.


A mother’s womb creates a separate and distinct environment for her baby. The placenta is the gatekeeper, generally allowing passage of important nutrients, hormones and other substances, while keeping dangerous substances out. Women know this isn’t a perfect system, it is up to them to avoid potentially harmful drugs and foods to better protect her growing baby. But one thing that is beyond a woman’s control is her own blood type or that of her baby.


Blood types – A, B, AB, or O – are either Rh negative (-) or positive (+). The Rh factor refers to the presence or absence of the Rhesus D antigen. An Rh- mother pregnant with an Rh+ baby who is exposed to some of her baby’s blood might then make antibodies against the Rh antigens. These antibodies will try to clean up any “invaders,” as the body sees these antigens, by destroying the red blood cells that carry them.


A mother who develops antibodies to the Rh factor is considered isoimmunized or sensitized and her body will be on extra alert for Rh+ cells in her body. Rh isoimmunization is only a concern for a woman with Rh- blood, an Rh+ woman is not affected – no matter what blood type her baby might be. It takes time after a blood exposure for maternal antibodies to develop and, since the most common time for exposure is birth, that baby would be born and out of danger from any harmful effects. This explains why Rh problems rarely develop in a first pregnancy. But in future pregnancies (and occasionally in first pregnancies) these antibodies on their clean-up mission can cross the placenta to begin working on the blood supply of a growing fetus, with deadly results.


Just a few generations ago, certain families just seemed to be plagued by pregnancy losses, often after a healthy, first child. They would not have known that the series of apparently random miscarriages or stillbirths was really the loss of their Rh+ babies, and their surviving babies would be those with Rh- blood. Because the Rh factor in blood wasn’t even discovered until 1940, there was no way to know which babies might be born very ill. It must have seemed so mysterious that a woman could have a baby born so very sick and might be followed by a pregnancy that was completely normal.


RhoGAM® was developed in the 1960s and was heralded as a miracle treatment. Women, who were given an injection of RhoGAM® (or RhIG) within 72 hours of giving birth to an Rh+ baby, were protected against developing antibodies, despite blood exposure. (Women who give birth to Rh- babies do not need RhIG.) Rh- women are also given RhIG after a miscarriage, abortion, ectopic pregnancy, abdominal trauma, amniocentesis, chorionic villus sampling or any time there is suspected bleeding in pregnancy.


With the initiation of RhIG and better treatment of affected babies, instead of 10,000 babies a year lost to Rh caused disease, the number plummeted. While the postpartum injection takes care of most Rh problems, there were still a very small percentage of women who became sensitized by the end of a first pregnancy even if there was no evidence of a possible blood exposure.


Currently all Rh- women are also offered a RhIG injection routinely at 28 weeks gestation to protect against any possible blood exposure near the end of pregnancy, even though the baby’s blood type is still unknown. Postpartum RhIG protects about 98% of women from developing antibodies and the 28-week injection makes it close to 99%. While the vast majority of women appreciate the almost 100% coverage with the addition of the routine 28-week injection, occasionally a woman might consider the small risk of isoimmunization without the 28-week shot not to be worth any possible risk from the RhIG injection itself and would rather get RhIG after birth, only if the baby is Rh+. RhIG carries a very small risk of hypersensitive reaction by the mother (i.e. anything from hives to anaphylaxis) and as a blood product there is a potential for transmission of a blood borne virus, as well as a religious objection for some. RhIG no longer contains thimerosal (mercury).


With the real dangers from Rh isoimmunization so far in the past, it can be easy to miss how almost miraculous this treatment can be for families.


Side Bar:

Discuss any questions about RhIG with your care provider


Laura Maxson, LM, CPM, the mother of three grown children, has been working with pregnant and breastfeeding women for over 30 years. Currently she is the executive director of Birth Network of Santa Cruz County and has a homebirth midwifery practice. Contact her at This e-mail address is being protected from spambots. You need JavaScript enabled to view it or This e-mail address is being protected from spambots. You need JavaScript enabled to view it

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