With the release of ASA Aberration, WildCard released an update making Reaper King baby levels based on a combination of player, mother and XP levels. I have worked out a rough formula for level distribution.

Reaper Queen Level + ( Player Level ÷ ( 155 ÷ Bonus Levels ) )

For example: A level 130 Queen, 91 player and 75 bonus Levels comes out to. (Current max attainable player level is 155, this may change with future expansions)

155 ÷ 75 = 2.0666~

91 ÷ 2.0666 = 44.046

130 + 44 ( rounded ) = Reaper King Level 174

Thanks to contributions of other tips, here is what I found useful:

1. You can gain bonus level XP while mounted. You do not need to run on foot to kill stuff while impregnated

2. Once the baby hatches and eats your body or dino body (if you use a pheromone), you can claim the baby then cryo it to prevent it from continuing to run. (This may be a bug)