My blood pressure has suddenly shot up

About 1% - 2% women develop what is commonly called transient high blood pressure during pregnancy. This type of hypertension is harmless and lasts only for the duration of your pregnancy. 
 

When should I be concerned about my blood pressure

Generally, blood pressure drops in the 1st and 2nd trimester and rises only in the 7th month. So if your systolic reading rises by 30mm Hg or the diastolic pressure rises by 15mm Hg, and stays up for 2 consecutive readings taken 6 hours apart, treatment is necessary. If it rises even higher in the 3rd trimester, and is accompanied by sudden weight gain, swelling and water retention, you could be suffering from pre-eclampsia (pregnancy induced hypertension). So report it to your doctor immediately.
 

What are the harmful effects of high blood pressure? Dr. Mansukhani

High blood pressure can cause stroke in the mother, growth retardation of the baby.  It can also result in premature delivery, which can be serious enough to cause loss of baby.