Final answer:
Concealed abruptio placentae often presents with no visible bleeding but may cause uterine tenderness, while external abruptio placentae usually involves vaginal bleeding.
Step-by-step explanation:
The distinction between concealed and external forms of abruptio placentae is characterized by the presentation of vaginal bleeding. For concealed abruptio placentae, there may be no visible bleeding because the blood is trapped between the placenta and the uterine wall, which can also cause uterine tenderness. In contrast, external abruptio placentae typically presents with visible vaginal bleeding as the blood escapes from the vaginal canal. Therefore, the correct answer to whether concealed or external form of abruptio placentae involves vaginal bleeding or uterine tenderness is option b: Concealed: No bleeding, External: Vaginal bleeding.