The pancreas is an endocrine and an exocrine organ. In the adult, the edocrine functions are performed by about a million islets of Langerhans. The islets are clusters of alpha, beta, delta and F cells.

"Diabetes and insulin resistance of pregnancy

One of the dominant metabolic effects of normal pregnancy is an increase in insulin resistance, probably induced by placental hormones including progesterone and placental lactogen. This leads to higher postprandial glucose concentrations that are considered to improve fetal growth; it is termed ‘facilitated anabolism’. Fasting glucose concentrations decrease as a result of placental glucose transfer and in the later stages of pregnancy, there is also enhanced maternal lipolysis. This is considered to spare glucose for the fetus and is termed ‘accelerated starvation’.

In genetically predisposed women, the normal insulin resistance of pregnancy may lead to the diagnosis of DM for the first time, termed ‘gestational diabetes’. This may disappear within hours of giving birth depending on individual factors such as islet β-cell function and predisposing factors such as obesity. Women with pre-existing DM require higher doses of insulin during pregnancy and patients who are usually controlled using oral hypoglycemic agents are transferred to insulin at this time.

The effects of pregnancy-induced insulin resistance in women with DM lead to poorer control of blood glucose and also an increased likelihood of ketoacidosis. The hyperglycemia in early pregnancy has considerable effects on the development of the fetal pancreas. Maternal ketoacidosis leads to fetal loss."

Glucose abnormalities in women with gestational diabetes mellitus (GDM) usually resolve postpartum, but commonly recur in subsequent pregnancies. Women with GDM have an increased risk of future development of overt diabetes.

Uncontrolled diabetes in pregnancy generally produces a large baby (macrosomia). Since the baby is able to produce all the insulin it needs, it takes in the glucose and stores the extra as fat. These babies are often too large to be delivered, except by assisted delivery and/or cesarean section

It is recommended that all women be screened for gestational diabetes in early pregnancy. The most common screening is the 50 gram glucose test. The woman drinks a glucose drink supplying 50 grams of glucose, and her non fasting blood glucose is measured an hour later. If her blood sugar is more than 140 mg/dl she gets further screening.

Unless there are risk factors in the woman's history, testing usually occurs around the 24th week. This is when the hormones from the placenta, that are opposing insulin, are at their peak. After delivery of the placenta, opposition to insulin ceases, and glucose and insulin production quickly return to prepregnancy state.

FYI, the NIH has a guide for Gestational Diabetes, that's directed toward toward the consumer.