Oooh, ooh ooh I know this one. Or at least, I received a fairly reasonable explanation.
When I was preggers, both times, I got a monster dose of the 'dropsies'.
I whinged about it to HV, and she held forth the following theory:
When you are pregnant, and at some times during your cycle, you can retain water. This can cause milimetre-fine expansion/contraction body-wide, and your brain, when making you pick up a cup, etc,is working with very fine tolerances, so the water-bloat can make you react a millimetre late, so to speak.
Did that sound rational? Not sure, but I've blamed every smashed glass since then on "medical grounds outwith my control".
In reality, it's probably because I'm sloppy