Diabetes insipidus (DI) is a medical condition caused primarily by "central diabetes insipidus", a hormonal defect, a defect of the hormone arginine vasopressin which is usually produced by the posterior pituitary gland in the brain. Not producing enough hormone by the pituitayt gland is also called "pituitary insufficiency".

A second cause of DI is a kidney dysfunction or "nephrogenic diabetes insipidus (NDI)", which is caused by an insensitivity of the kidneys or nephrons to antidiuretic hormone (ADH).

A third cause of DI is "gestational diabetes insipidus", DI that occurs during or shortly after pregnancy. Other causes of DI include DI caused by alcohol or some types of drug abuse. 

While diabetes insipidus and diabetes mellitus share a common first name, they are very different diseases and should not be confused with each other as they have different causes and treatments. Both have in common the word "diabetes" derived from the Greek work "siphon", and both are associated with "polydypsia", the production of too much urine. Diabetes mellitus is caused by inadequate amounts or responses of the pancreas hormone insulin, while diabetes insipidus is caused either by and inadequate production of antidiuretic hormone (ADH)  or the kidney's response to antidiuretic hormone. 

Diabetes insipidus is characterized by two major symptoms:

1. Polydypisa (excessive thirst)
2. Polyuria (excretion of large amounts of severely dilute urine)

Diabetes insipidus occurs in about 1 in 30,000 people, and gestational diabetes insipidus (Pregnancy-associated DI) is observed in about 1 in 30,000 pregnancies.

The symptoms of diabetes insipidus in pregnancy or postpartum  (gestational diabetes insipidus) are similar to the symptoms outside of pregnancy. During pregnancy, gestational DI is thought to occur with excessive production and/or impaired clearance of vasopressinase as the placenta produces the hormone vasopressinase.

In pregnancy, gestational diabetes insipidus can be associated with certain complications such as:

• pre-eclampsia,
• HELLP syndrome
• acute fatty liver of pregnancy

The cause of DI in these conditions can be caused by liver abnormalities leading to iimpaired clearance of circulating hormones such as vasopressinase. So if a women with gestational DI is first diagnosed in pregnancy, these conditions must be considered as part of the differential diagnosis, because treatment usually involves delivery of the baby.