These could include:
high blood pressure or hypertension
high blood sugar level or diabetes mellitus
high or low thyroid hormone levels
antiphospholipid syndrome or one of the familial thrombophilias (e.g. protein S deficiency, protein C deficiency, antithrombin III deficiency)
presence of anti-Ro or anti-La antibodies that may increase the risk of a heart block in the current pregnancy
systemic lupus erythematosus
Each of these medical conditions increases the risks for the mother and the fetus, and needs to be followed up carefully by the obstetrician with experience in looking after patients with such conditions.