Question (embryo development)

Ca
Would you say it's true that as long as hcg numbers are doubling, then the embryo/fetus is continuing to develop/grow? 
I had a 4w4d scan today and only the gestational sac was seen (which is completely normal for being this early). But I just have a fear that the baby will stop growing. But as long as hcg numbers are doubling, then the baby/embryo is alive, right? Or no?