Complications

Natalie • Married 11/14/15. 4 children. Mom of twins.
Has anyone experienced bleeding in pregnancy when the baby is measuring smaller than expected? My LMP puts me at 7 weeks tomorrow, but my doctor says the baby is measuring 4-5 weeks. I have been bleeding, but the baby's heart rate is steady. Just wondering if anyone has had a similar experience. We are hopeful, but also prepared. Doctor is calling this a threatened miscarriage