5wk 5d gestational sac only 4.8mm

Went to the doctor yesterday and my gestational sac only measured 4 wks 2 days old and I should be AT LEAST 5 weeks five days. They took blood to measure my progesterone levels which came back a 10 and my hcg levels and will draw more blood to compare tomorrow.

The doctor said that this could be a loss and the baby stopped growing at 4wks 2 days or that it's just a slow grower. I feel like she just said the last part to make me feel better. Has anyone ever had a baby that was a "slow grower"?!