If you have a blood pressure reading of 90/60 during the 21st week of pregnancy, it is important to consult with your healthcare provider. They will evaluate your overall health and determine the best course of action. Treatment options may include lifestyle changes such as increasing fluid and salt intake, wearing compression stockings, and avoiding standing or sitting for long periods. In some cases, medication may be prescribed to help regulate blood pressure. It is crucial to follow your healthcare provider's advice and attend regular check-ups to monitor your blood pressure throughout your pregnancy.