Final answer:
The hormone responsible for increasing maternal insulin resistance during the second and third trimesters is human placental lactogen, which ensures the fetus receives adequate nutrition by keeping maternal blood glucose levels high.
Step-by-step explanation:
The hormone responsible for increasing maternal insulin resistance during the second and third trimesters is human placental lactogen (hPL), also known as human chorionic somatomammotropin. This hormone is secreted by the placenta and plays a crucial role in regulating maternal metabolism to ensure adequate nutrition for the growing fetus. The presence of hPL leads to increased insulin resistance, resulting in higher levels of glucose in the mother's bloodstream, which can then be transferred to the fetus. It is a natural mechanism to prioritize the developing fetus's access to glucose, an essential nutrient for growth.
During pregnancy, other hormonal changes occur that can impact glucose metabolism, such as the increased production of cortisol by ACTH, which contributes to fetal protein synthesis, and increased secretion of insulin by the pancreas. If the maternal body's insulin is not enough to overcome the resistance created by hPL and other hormones, gestational diabetes may occur, which is a temporary form of diabetes that can develop in pregnant women.