In this study, the investigators will follow two small cohorts of pregnant women: a cohort of healthy women with uncomplicated pregnancies residing at high altitude, a control group of healthy women with uncomplicated pregnancies residing at sea level, to characterize differences in cardiopulmonary adaptation and nitric oxide (NO) pathway expression at elevations >3,500 m throughout pregnancy and into the postpartum period. The investigators aim to investigate right-sided cardiac impairment induced by chronic hypobaric hypoxemia, its effects on fetal growth, and the potential contribution of cardiovascular nitric oxide depletion to obstetric complications.

To investigate cardiac impairment, the investigators will perform transthoracic echocardiography in all enrolled pregnant women and infants, with a focus on right-sided cardiac anatomy and function, including pulmonary artery pressures, right ventricular thickness, right ventricular systolic performance, and indices of pulmonary vascular load.

To investigate the effects of hypobaric hypoxia on fetal growth, the investigators will measure intrauterine and post-delivery growth parameters, assess placental weight and histologic features, and correlate these findings with maternal oxygenation status and altitude exposure.

To assess nitric oxide production and consumption, the investigators will quantify nitric oxide-related metabolites (NO metabolomics) in maternal blood, umbilical cord blood, and placental tissue in both cohorts, and correlate these biomarkers with pulmonary arterial pressures, and right ventricular function. The investigators will also assess flow-mediated dilation in the high altitude cohort and relate these measures of endothelial function to pulmonary vascular and obstetric outcomes.

Inclusion Criteria:

• women delivering at participating hospitals at more than 3500 meters or women delivering at participating hospitals at sea level
• signed informed consent

Exclusion Criteria:

• preexisting cardiopulmonary pathologies (CHD, COPD, CKD, NYHA > III)

The cohort of healthy pregnant women residing at high altitude will selected from pregnant women who have lived at an altitude greater than 3500 meters throughout pregnancy and at delivery. The control group will be pregnant women who have lived at sea level throughout pregnancy and at delivery.