What causes increased insulin resistance during pregnancy?

Increased insulin resistance during pregnancy is primarily caused by human placental lactogen (hPL). This hormone is produced by the placenta and plays a critical role in modulating maternal metabolism to ensure that sufficient glucose and nutrients are available for the growing fetus. hPL acts on maternal tissues to promote insulin resistance, aiming to conserve glucose for fetal use while simultaneously stimulating lipolysis to increase free fatty acid levels for maternal energy needs.

The onset of insulin resistance also helps to ensure that maternal blood glucose levels remain elevated enough to support the metabolic demands of the developing fetus. This physiological adaptation is essential for the proper growth and development of the fetus, as it ensures that it has access to the nutrients it needs, even as maternal glucose utilization is modified.

In contrast, other factors listed, such as increased glucose clearance and decreased placental growth hormone, do not contribute to the mechanism of insulin resistance in the same direct manner. Elevated cortisol levels play a role in overall metabolism and stress responses but are not the primary drivers of the insulin resistance seen in pregnancy. Therefore, while they may impact insulin regulation, they do not directly cause the increased insulin resistance associated with pregnancy to the extent that human placental lactogen does.