Those pictures could have been taken when she was just a few weeks pregnant.
Btw, if you take FMD’s novel in a literal way, the Ann could not be Ann Dunham because the incident happened with his first wife.
He does talk about a man from Washington that was visiting Hawaii that liked to swing.
Excerpts from the novel can be found on the net.
,p> Hell they could be just a few minutes or so before she was pregnant