Jamie Lynn is Officially an UNWED MOTHER

The Spears posse walked into the Mississippi Southwest Regional Medical Center around 4:30 A.M. this morning ...the 6 lb 10 oz girl arrived just a few hours later. We're told Jamie Lynn was "extremely nervous" before the birth, and started to panic about going into labor. But big sister, bipolar Britney, who had flown in the day before, "made a big difference" and "helped a ton" -- giving her advice, support and encouragement.

The spawn will be called: Maddie Briann.