A pregnant woman at 32 weeks gestation is lying supine during a prenatal examination when she suddenly becomes pale, diaphoretic, and reports feeling dizzy and nauseous. Her blood pressure drops from 120/80 mmHg to 90/50 mmHg. What is the most important initial assessment the nurse should perform?

Supine hypotension occurs when the gravid uterus compresses the inferior vena cava, reducing venous return. Immediate left lateral positioning relieves compression and restores circulation, making it the priority over fetal monitoring or other assessments.

Understanding Supine Hypotension Syndrome
The scenario describes a classic presentation of supine hypotensive syndrome, also known as aortocaval compression syndrome. When a pregnant woman lies flat on her back, the weight of the gravid uterus compresses the inferior vena cava and abdominal aorta against the vertebral column. This mechanical compression reduces venous return to the heart, leading to decreased cardiac output, a sudden drop in blood pressure, and symptoms of shock such as pallor, diaphoresis, dizziness, and nausea. The drop from 120/80 mmHg to 90/50 mmHg is a hallmark sign of this condition, which is most common after 20 weeks of gestation .

Why Immediate Repositioning is the Priority
The most critical initial nursing action is to physically relieve the compression on the maternal great vessels. The correct choice, assessing maternal position and repositioning to a left lateral position, directly addresses the root cause of the hypotension. By shifting the uterus off the inferior vena cava and aorta, venous return and cardiac output are rapidly restored. This intervention is supported by the physiological principle of left uterine displacement, which is a standard prophylactic and therapeutic maneuver [1,2]. While a 15° left lateral tilt is frequently studied for prevention during cesarean deliveries, a full left lateral position is the immediate rescue measure for a symptomatic patient [2,3]. The effectiveness of any tilt angle relies on the fundamental concept of mechanically relieving aortocaval compression, which is best achieved by moving the patient off their back ^[4].

Analyzing the Alternative Options
Once the compression is relieved, other assessments can follow, but they are not the immediate priority. Checking the fetal heart rate (Option 1) is important because maternal hypotension compromises uteroplacental perfusion, but the fetal status will not improve until maternal circulation is restored. Fetal bradycardia is a late sign of this hypoperfusion. Obtaining a complete set of vital signs (Option 3) delays the critical, life-saving intervention of repositioning; the nurse already has enough data (a significant drop in BP with classic symptoms in a supine patient) to act. Evaluating for signs of preeclampsia (Option 4) is not the most immediate concern. While preeclampsia can involve hypertension, this patient is hypotensive, and her symptoms are positional and directly correlated with lying supine, making aortocaval compression the clear etiology. The immediate nursing action is a non-pharmacological, mechanical intervention that resolves the crisis [1,2].