The Effect of Different Delivery Positions on Pelvic Floor Function.

Inclusion Criteria: 1. Aged 20 to 40 years. 2. Singleton, cephalic presentation, full-term primipara. 3. Absence of cephalopelvic disproportion. 4. Estimated fetal weight (EFW) \< 4000 g. 5. Intended vaginal delivery and scheduled for postpartum follow-up at our hospital. 6. Voluntary participation with provision of informed consent. Exclusion Criteria: 1. Moderate or severe stress urinary incontinence prior to pregnancy. 2. Pelvic Organ Prolapse Quantification (POP-Q) stage ≥ III, or a history of treatment for pelvic floor dysfunction. 3. Uncontrolled systemic medical diseases, or a history of asthma, allergic rhinitis, and constipation prior to pregnancy. 4. Presence of contraindications to vaginal delivery. 5. Presence of contraindications to the Valsalva maneuver (e.g., severe cardiopulmonary diseases, cervical incompetence, etc.). Withdrawal Criteria: 1. The patient's clinical condition becomes unsuitable for continued study participation and follow-up. 2. The subject requests to withdraw from the study.