I finally organised all of baby's clothes in her dresser and then it hit me, should I have pre-washed them all before she's born?

Yes, you should wash baby's clothes, blankets, and other washable items that will come in contact with his or her skin. It's not necessary that you do it before she's born, but it is recommended that you do it before she wears them. The reason for this is that baby's brand new birthday suit hasn't toughened up yet. Her skin is sensitive and the finish that's put on new clothes to make them look cute enough for you to snatch up can irritate baby’s virgin skin.