Which condition may NOT contribute to variable decelerations?

Variable decelerations are primarily associated with umbilical cord compression, which can occur due to various fetal and maternal conditions. In this context, maternal dehydration is generally less likely to be a direct contributor to variable decelerations as compared to the other conditions listed.

Cord prolapse results in variable decelerations because it exposes the umbilical cord to pressure from the presenting part of the fetus. Tachysystole, characterized by an increased frequency of contractions, can also lead to compression of the umbilical cord and subsequently contribute to these decelerations. A short umbilical cord may lead to similar issues, as it might be more prone to compression during contractions or fetal movements.

Maternal hydration is important for maintaining adequate blood flow and oxygenation to the fetus, but dehydration itself does not typically lead to cord compression or direct mechanical impacts on fetal heart rate. Thus, while dehydration can affect fetal well-being through other mechanisms, it does not directly contribute to variable decelerations in the same way that the other listed conditions do.