Some women develop what is called 'gestational hypertension'. This is a slightly raised blood pressure that is first noticed after 20 weeks of the pregnancy that often continues for up to 3 months after the birth. The blood pressure is at a higher level than expected, but not enough to require medications or to affect the woman's health (like 'pre-eclampsia'). Women with gestational hypertension and their babies are normally quite well and are not generally affected. If you have gestational hypertension, you may be monitored a little more closely to make sure it doesn't develop into pre-eclampsia.
High blood pressure before pregnancy
A few women will have high blood pressure before their pregnancy. This is known as 'essential hypertension'. You may already be aware that your blood pressure is higher than normal or it may be something that has been detected at a preconceptual health check (or at the first pregnancy visit, before 20 weeks).
Essential hypertension detected during pregnancy shows the blood pressure being unexpectantly higher but no fluid swelling (called 'oedema') and no protein detected in the urine (which happens with high blood pressure associated with being pregnant, or 'pre-eclampsia'). Essential hypertension is more common in older women, women who smoke and/or women with a family history of high blood pressure and sometimes if you had high blood pressure with a previous pregnancy.
Other medical conditions that may cause high blood pressure before (or during early) pregnancy are kidney disease, heart disorders, or very rarely a molar pregnancy. If your high blood high blood pressure is caused by another health condition it is referred to as 'secondary hypertension'. Women who were previously unaware of their high blood pressure will usually have additional blood tests to rule out other possible health conditions.