I realise this is me being a bit paranoid but, when your baby hiccups in the womb are the hiccups really close together? like every second or so? Much more close together than you would usually hiccup.
Reason I ask is because dd has epilepsy and one of the specialists I saw for this pregnancy asked me if I had felt dd having seizures inside me. It has just got me a bit worried and although I am fairly confident this baby is just hiccuping, there is a tiny part of me worried that it might be seizing.