What substance in the plasma increases during pregnancy and correlates with fetal and placental growth?

Human placental lactogen (HPL) is a key substance produced by the placenta during pregnancy. Its levels increase significantly as the pregnancy progresses and are closely associated with fetal and placental development. This hormone plays a crucial role in modulating maternal metabolism, promoting the supply of glucose and amino acids to the growing fetus, and stimulating mammary gland development in preparation for lactation.

The increase in HPL is vital for ensuring that the developing fetus receives adequate nutrients, supporting its growth, while also adjusting the mother's metabolism to accommodate pregnancy. This is particularly important as the placenta grows and its functions expand to support the fetus.

While estrogen, progesterone, and relaxin also rise during pregnancy and serve important roles, each has distinct functions and does not correlate directly with both fetal and placental growth in the same way that HPL does. Estrogen is primarily involved in various aspects of pregnancy maintenance and uterine growth, progesterone is crucial for maintaining the uterine lining and preventing contractions, and relaxin primarily aids in softening the cervix and pelvis in preparation for labor. Therefore, HPL stands out as the substance most directly linked to the growth and development of both the fetus and the placenta during pregnancy.