Pregnant Kristin Cavallari -- Knocked Up in the Rain

Just one day after announcing her pregnancy, a freshly knocked up Kristin Cavallari ventured out in the L.A. rain this morning -- grinning with pride over the embryonic cells rapidly splitting in her uterus.

25-year-old Kristin and her 28-year-old baby daddy Jay Cutler broke off their engagement in July -- but rekindled things shortly after in November ... with a vengeance, apparently.