here's some info. i found on the web about this topic.
Vasa previa is a rarely (1:3000) reported condition in which fetal blood vessel(s) from the placenta or umbilical cord crosses the entrance to the birth canal, beneath the baby. The condition has a high fetal mortality rate (50-90%). This can be attributed to rapid fetal exsanguination resulting from the vessels tearing when the cervix dilates, membranes rupture or if the vessels become pinched off as they are compressed between the baby and the walls of the birth canal.
The aberrant vessels result from:
Velamentous Insertion of the Umbilical Cord
Little is known about the cause of these conditions. The most widely recognized theory is called trophotropism. According to Dr. Harris Finberg, trophotropism in placental tissue can be compared to the tendency of a plant to lean towards the sun to get the light it needs to survive. Since the lower segment of the uterus is not as nourishing as the upper segment, the placenta will grow upwards to reach more nourishing tissue.
In bilobed/succenturiate lobed placentas, the placental tissue may erode from the cervix, but vessels don't. With velamentous insertion of the cord, the mass may erode and the new growth may occur away from the location where the cord inserts, connected by unprotected bloodvessels.
Vasa previa often appears together with a low-lying placenta or Placenta Previa, where the placenta is in front of the birth canal.
Vasa previa might be present if any (or none) of the following conditions exist:
low-lying placentas (may be caused by previous miscarriages and/or curreting of the uterus (D&C), which causes scarring in the uterus)
pregnancies resulting from in-vitro fertilization
When vasa previa is detected prior to labor, the baby has a much greater chance of surviving. Since vasa previa is rarely detected prenatally (an estimated 70-90 percent of cases are undiagnosed), survival rates are not available.
Vasa previa can be detected during pregnancy as early as the 16th week of pregnancy with use of transvaginal sonography in combination with color Doppler.
When vasa previa is diagnosed, elective delivery by cesarean before labor begins can save the baby's life. Exactly when to schedule the c-section should be decided by the patient and her doctor. Ideally, it should be performed early enough to avoid an emergency, but late enough to avoid problems associated with prematurity.
Steroid treatments can help accelerate the maturation of the baby's lungs. An amniocentesis can assess fetal lung maturity.
When there is bleeding during pregnancy, investigation for the source of the blood is necessary. If the blood is determined to be maternal (from the mother), the baby is not in danger. If the blood is determined to be fetal (from the baby), immediate action must be taken to assess the condition of the baby.
i hope this helps. interesting subject. i think you did the right thing, especially when you consider what could've happen if your suspicions were true.