Arm Position and Blood Pressure Measurement Accuracy During Pregnancy

Blood pressure measurement is a routine and essential component of prenatal care and plays a central role in the diagnosis and management of hypertensive disorders of pregnancy. International and national guidelines recommend measuring blood pressure with the patient seated, after a period of rest, and with the arm supported at heart level. Despite these recommendations, blood pressure in clinical practice is frequently measured with the arm placed in non-standard positions, which may lead to inaccurate readings and potential misclassification of blood pressure status.

This study is designed to assess the effect of arm position on blood pressure measurements in pregnant women. This is a single prospective randomized crossover trial conducted across all three trimesters of pregnancy. Randomization of arm position order is performed using a computerized block randomization system with stratification by trimester (first, second, third) and chronic hypertension status.

Participants are enrolled during routine visits to a high-risk pregnancy clinic and are assigned to a trimester-specific cohort based on gestational age at the time of enrollment. During a single clinic visit, each participant undergoes multiple blood pressure measurements with the arm positioned in several commonly used positions: supported on a desk at heart level, supported on the lap, and unsupported at the side. To account for natural variability in blood pressure measurements, an additional set of measurements with the arm supported at heart level is obtained. Each participant serves as her own control within the randomized crossover design.

Blood pressure measurements are performed by trained nursing staff using a clinically approved automated blood pressure device, following a standardized measurement protocol. All measurements are obtained after a resting period and while the participant is seated comfortably.

Participants are recruited across all three trimesters, and analyses are conducted separately by trimester. The primary outcome is the difference in systolic and diastolic blood pressure measurements between arm positions. Secondary analyses evaluate the magnitude and pattern of blood pressure differences across gestational ages and relevant clinical subgroups.

This study involves minimal risk and does not alter standard clinical care. The results are intended to improve understanding of how arm positioning influences blood pressure measurements during pregnancy and to inform best practices for accurate blood pressure assessment in prenatal care.

Inclusion criteria

• Pregnant women aged 18 to 55 years
• Singleton or multiple viable intrauterine pregnancy
• Gestational age corresponding to first, second, or third trimester at the time of enrollment
• Ability to sit upright comfortably for the duration of blood pressure measurements
• Ability to understand the study procedures and provide written informed consent

Exclusion criteria

• Preexisting significant cardiac disease (e.g., arrhythmias, congenital heart disease, severe valvular disease)
• Chronic kidney disease defined as serum creatinine ≥1.5 mg/dL at enrollment
• Significant upper limb or shoulder conditions that may affect arm positioning or blood pressure measurement (e.g., lymphedema, fractures, prior surgery, arteriovenous fistula)
• Neurological or musculoskeletal conditions preventing proper positioning
• Severe preeclampsia, eclampsia, or other acute medical conditions requiring immediate intervention
• Major fetal anomaly
• Intrauterine fetal demise