Effect of Epidural Hydromorphone Combined With Ropivacaine in Labor Analgesia

The purpose of this study is to compare the effects of three different doses of hydromorphone combined with ropivacaine and sufentanil combined with ropivacaine in epidural labor analgesia through prospective clinical trials, so as to explore whether hydromorphone combined with ropivacaine has advantages in epidural labor analgesia, and find out the optimal dose of hydromorphone. Participants will be randomly allocated to four groups: H1 group,H2 group,H3 group and SF group.For those in H1 group: they will be administered with15 ug/ml hydromorphone and 0.08% ropivacaine for epidural labor analgesia, For those in H2 group: they will be administered with17.5 ug/ml hydromorphone and 0.08% ropivacaine for epidural labor analgesia, For those in H3 group: they will be administered with 20 ug/ml hydromorphone and 0.08% ropivacaine for epidural labor analgesia, For those in SF group: they will be administered with 40 ug/ml sufentanil and 0.08% ropivacaine for epidural labor analgesia. The goal of this clinical trial is to provide a new treatment option for pregnant women in epidural labor analgesia, and to provide a basis for hydromorphone combined with ropivacaine in epidural labor analgesia.