You may be thinking of Freydís Eiríksdóttir and her (alleged) experience in Vinland.

As men fled during the confusion, Freydís, who was eight months pregnant, admonished them, saying: “Why run you away from such worthless creatures, stout men that ye are, when, as seems to me likely, you might slaughter them like so many cattle? Let me but have a weapon, I know I could fight better than any of you.”

Ignored, Freydís picked up the sword of the fallen Thorbrand Snorrisson and engaged the attacking natives. Surrounded by enemies, she undid her garment and beat the sword upon her breast.