Congratulations on your pregnancy! Honestly, 16 weeks pa, baru la dia start bergerak so it could be baby movement, tapi berdegup atau bergetar biasanya lebih likely Braxton Hicks contractions or just your body adjusting to the pregnancy, my first time juga I was so paranoid thinking every sensation was the baby Best to mention it to your doctor at your next checkup, especially if it happens often or ada pain, but most likely normal lang.