During pregnancy, the second trimester ranges from:

Human pregnancy has an average duration of about $40$ weeks, which is divided into three trimesters.

The first trimester ranges from the $1^{st}$ week to the $12^{th}$ week.

The second trimester ranges from the $13^{th}$ week to the $26^{th}$ week.

The third trimester ranges from the $27^{th}$ week to the $40^{th}$ week.

Therefore, the second trimester ranges from the $13^{th}$ to the $26^{th}$ week.

Answer: $13^{th}$ to $26^{th}$ week