These may be symptoms of a migraine or they could be symptoms of pre-eclampsia, which is a condition that normally occurs after 20 weeks of pregnancy with raised blood pressure. You might also have other symptoms such as a bad headaches, stomach pain, nausea and vomiting. Pre-eclampsia is potentially dangerous for you and for the baby.
Call your midwife immediately.
Read more about pre-eclampsia
National Institute for Health and Care Excellence, Hypertension in pregnancy, clinical guideline 107, London NICE, 2011