Why do some women get diabetes when they are pregnant? Is this dangerous for them or their baby?

Pregnancy is a situation in which insulin resistance (see Question  2) is a normal feature. This is because it is beneficial for the  nutrients absorbed from a pregnant woman’s  meals to be  channeled first to the growing fetus. The development of  maternal insulin resistance in the second half of pregnancy  assures that this will occur. At least part of the reason for the development of maternal insulin resistance is that the placenta pro- duces substances that lead to insulin resistance and as the  placenta  grows, the  insulin  resistance increases. This is called  physiologic (i.e., normal) insulin resist- ance. Indeed, a healthy pregnant woman may be more insulin resistant than the average  patient with type 2 diabetes! However, the vast majority (>95%) of other- wise healthy pregnant women do not get diabetes in this  situation  because the  pancreas is  able to  make enough insulin to overcome the insulin resistance and keep the glucose  levels normal. A small minority of women cannot do so and their glucose levels rise. These women tend to be the same women who are destined to get type 2 diabetes later in life. The risk of develop- ing type 2 diabetes is much higher in a woman who has had diabetes detected in pregnancy ( gestational dia- betes mellitus or  GDM).  GDM  provides a  unique opportunity to follow the natural history of type 2 dia- betes in  the years prior to its onset in women, since most GDM goes away very rapidly, often within hours, after the baby is delivered and reappears in later life as type 2 diabetes. If untreated, GDM can cause harm to both mother and baby, especially at or soon after deliv- ery. Fortunately, outcomes of GDM are generally excel- lent in most developed countries.