My midwife told me that the movements themselves might feel different as baby gets bigger, more sweeping and stretching than punchy and sharp, but that the pattern itself shouldn't really change. I agree with Clare, make the call now, and get you and baby checked over. It really is better safe than sorry, and the midwives will not mind at all checking you both over.
I've been in to be checked for exactly the same thing and the midwives on my MLU could not have been more lovely with me, and even though there was clearly nothing wrong (baby was doing the macarena inside me by the time they hooked me up to the monitors) they told me it was the right thing to do, and should i ever be worried again to do exactly the same.