How valid is the 1st day of your last period to determine how far along you are?

Vanessa

Question. So the 1st day of my last period was June 19. This had me at 6 weeks and 4 days today. My doctor wrote in the ultrasound 3/25 as the due date based on the june 19 date. I should be 6 weeks and 4 days.

So I went to my obgyn appointment on friday. Gave them the info above and expected to see a 6 week 4 day image.When we did the ultrasound i was only measuring approx 4 weeks. The only thing we saw was the gestational sac and the yoke sac of cells. She said i was more like 4 and scheduled me for 2 weeks from now. I know for a fact my period was on june 19. Why am i measuring so early? Is the baby still growing? Did it stop? Its never happened before. With my son i went in at what would be 8 weeks according to 1st day of last period and measured 8 weeks. With my miscarriage i gave them my date and went in on the "6"week and measured 6. This is the first time that I dont. I went in at 6 and measured approx 4. Im thinking maybe it has stopped growing. Mayb it is spontaneous. Idk.