This is where the structure of the passage pivots (chiasm, or, introversion) giving it emphasis and making it the center of attention. When you compare these matching elements at the pivot, it is immediately apparent that verses 17 and 18 resolve further into a repeating set. (ab a?b?. When we give consideration to how the matched elements compare and contrast, we are led to see verse 19 as a partial match, drawing us to inquire of the Author about the meaning of the asymmetrical pattern. Why are the women who are pregnant or nursing babies given no specific direction, like those others who might be on the housetop or in the field, which would be beyond the more general direction that is to pray about the timing of the flight, and in connection with that, of the ABOMINATION OF DESOLATION itself?