It's actually quite a good question, and I'm not sure anybody has any answer to it.
We talk extensively about nitrogen bubbles in blood, and the damage they do or may do when carried to various places. Obviously, nitrogen also transfers across cell membranes and into cytoplasm, and has the possibility to bubble there as well. I don't know where seed nuclei are posited to be created or to exist, but I know that motion has been implicated in their formation. Since there is little or no motion within an individual cell, perhaps they don't form there?
As far as damage done to a fertilized egg, as opposed to unfertilized ova sitting in the ovaries, one could certainly offer the explanation that a fertilized ovum is one of the most metabolically and reproductively active cell masses in the body -- and every cell division is an invitation for DNA copy error (which is, of course, one of the reasons teratogens are so effective early in pregnancy).
The bottom line is that we don't know, and there is almost certainly no imperative or funding for investigating this further, since the solution of avoiding diving while pregnant or trying to become pregnant is a simple one.
I did not mean to be judgmental, but a one month delay to allow you to enjoy your trip did not seem unreasonable to me (but it may to you) and would avoid all the questions.
