I have diabete type one. why a few days before period my blood sugar level become high?

Very common: Resistance to Insulin increases shortly before and usually through the first day or two of a menstrual period. This causes an increase in blood sugars. To compensate, many of our patients are given Insulin dose increases to accommodate for the Insulin resistance to keep blood sugars more normal. Please discuss with your doctor.

Changes in hormones: Several studies show that the pre-menstrual interval (3-7 days before period) may be associated with higher blood sugar levels in insulin-requiring women with diabetes. This may be related to hormonal changes (estrogen and progesterone) occurring during the monthly cycle that affect Insulin resistance. Some patients need to routinely increase their Insulin doses during these monthly occurrences.