To Stress, To Stress Out, To Be Nervous
する verb
緊張 is stress. So, the verb version is to stress out.
きんちょうする
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
赤ちゃんが逆子で産まれてくるって分かってたので、出産時は緊張しました。
I was nervous during delivery because I knew my baby was going to be a breech birth.