This randomized clinical trial aims to compare the effect of the left lateral decubitus position versus the supine position on the duration of the active phase of labor in nulliparous women. A total of 188 participants will be randomly assigned to one of two groups. The intervention group will be placed in the left lateral decubitus position, while the control group will remain in the supine position. Both positions will be maintained for 30-minute intervals with 5-minute rest periods, continuing until delivery. The primary outcome is the duration of the active phase of labor. Secondary outcomes include rates of cesarean section, use of oxytocin and analgesics, and maternal and neonatal complications.

Globally, maternal positioning during labor is a key component of humanized childbirth. While the World Health Organization recommends allowing women to adopt comfortable positions, the supine position remains prevalent in many clinical settings for practitioner convenience. This study in Honduras seeks to generate local evidence on the impact of maternal position on labor progression. Nulliparous women at term (≥37 weeks) with a singleton pregnancy in cephalic presentation and in the active phase of labor (≥6 cm dilation) will be recruited from the labor and delivery unit of the Hospital Materno Infantil. After providing informed consent, participants will be randomized. The primary efficacy endpoint is the time from the onset of the active phase (or intervention start, if later) until delivery. The study hypothesizes that the left lateral position will significantly reduce active labor duration compared to the supine position, potentially reducing unnecessary surgical interventions and improving the childbirth experience.

Inclusion Criteria:

• Signed and dated informed consent form.
• Nulliparous woman.
• Singleton pregnancy at ≥37 weeks of gestation.
• Intact amniotic membranes.
• Cephalic presentation.
• In the active phase of labor (cervical dilation ≥6 cm).
• Age ≥18 years.
• No contraindication for vaginal delivery.
• Possession of a mobile phone (for potential follow-up contact).

Exclusion Criteria:

• Previous uterine surgery.
• Maternal condition preventing vaginal delivery.
• Fetal anomaly.
• Premature rupture of membranes.
• Multiple pregnancy.
• Fetal demise.
• Uterine myomas.
• Maternal comorbidities (e.g., chronic hypertension, diabetes mellitus type -1/2/gestational, hypothyroidism).
• Anemia.
• Age <18 years.
• Preterm gestation (<37 weeks).

Eligibility is based on sex, not gender identity.

The research team acknowledges the importance of data sharing but has not yet established the necessary infrastructure, resources, and legal/ethical agreements required for the secure preparation, anonymization, and controlled sharing of individual participant data (IPD). Decisions regarding future sharing will depend on internal review, compliance with Honduran data protection regulations, and securing appropriate funding and technical support for long-term data stewardship.

The groups will be labeled "AGroup" and "B Group" during data collection and tabulation. The statistician performing the analysis will be blinded to which group corresponds to which intervention until the analysis is complete.