I have heard from many women that during pregnancy, their feet became unbearably ticklish. Once I was even talking to a bank teller and had steered the conversation toward tickling. She said her feet were not ticklish with the exception of when she was pregnant. She claimed that she was so surprised when her boyfriend tried to massage her feet, but she couldn’t handle it. She had to make him stop because she absolutely wasn’t used to having ticklish feet.
Feet grow and shrink during pregnancy. The swelling, the extra weight, the fluctuating hormones. I would imagine all the conditions are there to exacerbate any pre-existing ticklishness.