Lost 4 pounds

So I was at a normal BMI before pregnancy.... I gained weight at a normal rate throughout this pregnancy (20 lbs ) except for losing 7 in the beginning, which I was told, is very normal. I am 38+4 now and I still eat the same as I have during the entire pregnancy. In 5 days I have lost 4 pounds!! Baby is still moving okay and I am not leaking. Does a spike of metabolism happen during this time? Has this ever happened to any of you? What have your OB's said about it?