Measuring 31 at 35w3d

Kirsten
Has anyone else been told they are measuring small and got to go for growth scan? I was measuring bang on and then last couple weeks just been 1 less which is fine, last appt I was measuring 32 at 33w3d. But today at 35w3d im measuring 31....weird that I've actually got smaller? Baby's head is now engaged so wondering if that's why measurements are a bit lower?