Being curious as to why doctors would subscribe the shot at 28 weeks, I researched and found this:
RhoGAM: Options on need at 28 weeks
Q: I'm 29 weeks pregnant and Rh-negative; my husband Rh-positive. I live in Norway, but during my trip home to the U.S., a doctor advised me to have a RhoGAM injection at 28 weeks. My doctor in Norway says there is no need to give RhoGAM during the first pregnancy because I will get it within 48 hours after delivery if the baby tests positive. Please clarify.
A: Within the past 10 years or so, more data have indicated that when providers administer RhoGAM at 28 weeks and again after the birth (if the baby is Rh positive), the rate of Rh hemolytic disease of the newborn is cut to almost nothing. About two percent of Rh negative women still become immunized against their baby's blood despite RhoGAM administration after their last birth. With RhoGAM at 28 weeks, the rate is now seven-tenths of a percent.
I believe that the U.S. recommendations will become the norm some day, but for now, you are still at a low risk if you receive the injection after birth or with any procedures prenatally or bleeding episodes.
I also found this site:
The Risk is Low
At first you may be scared. If you have Rh- blood and your baby is Rh+, your body could hurt your baby! But in reality, the chances of that happening are very slim. Your blood and your baby's blood do not mix. They flow side by side, but separated by a thin membrane. Since the blood doesn't mix, no antibodies are manufactured by your body.
Certain things can cause a mother and baby's blood to mix. Sometimes a mix occurs during miscarriage, amniocentesis, chorionic villi sampling (CVS), or major trauma (such as a direct fall on the belly or a car wreck). Mixing can also occur during birth. It's rare during a natural birth where the placenta is allowed to separate on its own. However, interventions increase the risk that a mother and baby's blood will mix.
The 72 hour limit means that any shot given in the prenatal period is probably arbitrary. Doctors must admit that the 28 week dose (and 36 week with some doctors) is simply given at a random date chosen with the hope that it may protect some babies. An injection given after a known trauma is much more effective and makes much more sense.
...In reality, being given a routine dose of a human blood product at 28 weeks is not the best way to protect babies from Rh disease. There's only a slim chance that any major "trauma" will have occurred during the 72 hours before the injection.
A woman is free to reject or accept any combination of Rhogam (for instance, she can refuse it prenatally and still have it after birth). If a woman chooses not to have Rhogam, there are steps she can take to make it more likely that her blood and her baby's do not mix.
One of the first and easiest things to do is to ensure an excellent prenatal diet. A good diet will ensure that your baby and your placenta develop well and that your systems interact the way that they were meant to. Enjoy blood building foods such as beets, cherries, buckwheat, dark leafy greens, and sea vegetables during pregnancy.
Drinking Red Raspberry Leaf tea is beneficial throughout the second half of pregnancy. It helps tone the uterus for labor. This will help keep blood loss at a minimum during and after birth. Drinking citrus juices and selecting vitamin C rich foods is believed to help keep the placenta strong and healthy.
Eliminating fluoridated water is also recommended as fluoride has been shown to interfere with collagen production. Collagen is what the placenta is firmly attached to the uterus with. A natural, intervention free birth is the best birth for an Rh- mother wishing to avoid Rhogam.
A completely natural birth gives the lowest risk of maternal and fetal blood mixing. Wait for the cord to stop pulsing before it is cut. This allows most of the blood to flow into the baby's body.
The third stage of labor is possibly the most vital part of labor to keep natural. Allow the placenta to separate naturally and be born gently. Strong contractions will help the placenta to shear cleanly off the surface of the uterus and continued contractions will seal off the blood vessels. A mother can squat and birth the placenta gently. If the placenta has fully separated, very gentle cord traction may bring it out.
If the birth is natural and the placenta is born gently, the chances of mother and baby's blood mixing are very low, and so the risk of maternal sensitization is also quite low. Blood can be drawn from the umbilical cord to determine the baby's blood type.
The lady who wrote this last section has her own website to promote natural birth: http://www.naturalbirthandbabycare.com/. I understand she's vegan, but she has some good points! *;o)
If any of you find any REAL reason to have the RhoGAM shot at 28 weeks, please leave me the information. I understand the point of the shot, just not the timing that most doctors recommend...