Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services if you faint, have severe abdominal pain, become confused, or have heavy bleeding with signs of collapse.
These symptoms can occur with major blood loss or a ruptured ectopic pregnancy.
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Contact a maternity, early-pregnancy, or urgent healthcare service promptly about any new bleeding in pregnancy.
This is particularly important if the pregnancy has not yet been confirmed inside the womb.
Seek urgent medical assessment if:
Bleeding becomes heavy or repeatedly soaks through sanitary pads
Pain is severe, worsening, or mainly on one side
You pass large clots or pregnancy tissue
You have shoulder-tip pain
You develop fever, chills, or unpleasant-smelling discharge
You feel very weak, dizzy, short of breath, or generally unwell
Seek further advice sooner if the pattern changes.
The article also says
For light bleeding without severe symptoms, follow the assessment and repeat-testing plan given to you.
Every sign above is quoted from the sofidex article on Miscarriage - threatened. If you are not sure, err upward — it is always reasonable to be checked.