Complex sentence: During Húrin's imprisonment Túrin was sent to live in the Elf-realm Doriath by his mother out of fear for his life and in the absence of her husband and her son, Morwen gave birth to her third child, Niënor, a girl.
Split into simpler sentences: During Húrin's imprisonment Túrin was sent by his mother to live in the Elf-realm Doriath for protection. In his absence Morwen gave birth to her third child, Niënor, a girl.