You blood pressure is so important during the 2nd trimester of pregnancy because this is when many blood pressure related complications begin to develop. High blood pressure can cause and aggravate problems like preeclampsia and gestational diabetes. Preeclampsia and gestational diabetes can cause problems to your child's nutrition and blood sugar levels. Your doctor can diagnose gestational diabetes through a glucose challenge test. Your doctor can diagnose preeclampsia by observing your symptoms and your blood sugar.