I am currently 30 weeks pregnant with my first baby. Following my 23 week scan, I know I am having a little boy. Two of my very good friends have recently had baby girls. They both had (have) a linea nigra, and I don't. Out of interest, I have asked around and I now know 3 other cases where with boys the Mums did not develop a linea nigra, and 2 other cases where the Mums had linea nigras with girls.
My friends and I realise that something like this is unlikely to have been missed by all those doctors and scientists, but hey, out of fun.. can anyone back this theory up??