Sayang, fetal heart rate changes tu boleh normal, tapi sebab ni first baby and you're concerned, please call your gynae or go in for a check-up , tak payah tunggu, just to make sure everything okay. Better safe than sorry, especially at 38 weeks kan. A few of my mum friends pun pernah experience slight dips and the doc reassured them it was fine, but doktor perlu dengar and check properly, so jangan delay ye. Praying everything's smooth for you!