it's usually not dangerous. it happens very early in the pregnancy, that some ppl don't even realise yet that they were pregnant. the symptoms to expect are a heavier than usual period with cramping. The HCG levels will immediately drop too, and should test negative in the next 2 days. I went through it, we were determined to try again and managed to conceive the following month. Jiayou and take care!!
how do you define dangerous? it means the embryo stops growing