This is an interventional study that will test whether a breathing exercise called Inspiratory Muscle Strength Training (IMST) can safely and effectively lower blood pressure during late pregnancy. The goal is to see if a home-based breathing training can help prevent or reduce high blood pressure disorders in pregnancy. The main objectives are to make sure the training is safe and tolerable for pregnant women and to examine blood pressure and blood vessel health. Participants in their third trimester will be randomly assigned to either do moderate resistance IMST or a minimal resistance sham IMST, for 5 to 8 minutes a day over six weeks.

Inclusion Criteria:

• Female sex
• Pregnant (32 to 34 weeks of gestation, confirmed by ultrasound, at the time of first training session, eligible patients may consent/enrolled earlier in pregnancy)
• Singleton pregnancy
• Age 18 to 55
• Able to read English and provide consent
• Possess smartphone for syncing the AiroFit and Omron devices using Bluetooth and completing online surveys
• Smartphone updated to iOS 12+ or Android 11+
• No contraindication for moderate exercise at time of enrollment
• Not planning delivery for at least one month at time of enrollment (< 38 weeks of gestation)
• Willing to adhere to AiroFit device use throughout study period
• Must already be scheduled, or in the process of scheduling, for weekly NST appointments by 32 to 34 weeks gestational age (per provider order / due to obstetric indication)

Lower-Risk Pregnancy Cohort Inclusion Criteria:

• No history or evidence of hypertensive disorders of pregnancy
• May be undergoing antenatal testing for:
• Conception via in vitro fertilization, BMI ≥ 35, an advanced maternal age (age >/=35), or other condition not listed in exclusion criteria or 'higher risk for HDP group' but is recommended for antenatal testing.

Higher-Risk Pregnancy Cohort Inclusion Criteria:

• Conditions associated with higher risk of developing HDP, including:
• Gestational diabetes mellitus, chronic hypertension, gestational hypertension, or a history of preeclampsia in a previous pregnancy

Exclusion Criteria:

• Younger than 18 or older than 55 years of age
• Multiple gestation (twin or higher-order pregnancy)
• Fetal chromosomal abnormalities or major anatomical anomalies
• Planning to deliver earlier than 38 weeks or within 4 weeks of study enrollment
• Any contraindication for moderate exercise (e.g., cardiomyopathy, congenital cardiac conditions)
• Deep vein thrombosis
• Complications in current pregnancy including intrauterine growth restriction (IUGR), oligohydramnios, preeclampsia, or severe-range blood pressures (>/=160/110 or <100/60)
• Active vaginal bleeding, or history of coagulopathy
• Placenta previa or other placental abnormalities (including placental cyst or abruption)
• Signs of labor
• Current substance use disorder
• History of neurological, respiratory, head/neck, or thoracic surgeries, or conditions such as collapsed lung or perforated eardrum
• Individuals with any of the following:
• Chronic obstructive pulmonary disorder (COPD)
• Severe asthma
• Severe ischemic heart disease
• Left-sided heart failure
• Chronic laryngitis, chronic bronchitis, emphysema, pneumonia
• Latent or active tuberculosis
• Chronic cough
• Neurological problems (e.g. seizure disorder)
• Severe scoliosis with no history of surgical correction or management.
• Organ transplant
• HIV or other immunocompromising conditions
• Autoimmune disease with possible vascular complications (e.g. Lupus)
• Significant respiratory compromise (e.g., severe dyspnea, O₂ saturation <95%, uncontrolled asthma, history of pneumothorax)

All IPD that underlie results in a publication will be shared, after any identifying information is removed from the dataset.

Upon publication, for a period of 2 years, the IPD will be available using a publicly available repository/storage system (e.g. Open Science Framework or similar).

Any data that is made publicly available can be accessed without permission/restriction. Beyond the initial 2 year period, data can be made available upon reasonable request to the PI.