What does a non-stress test evaluate during pregnancy?

A non-stress test primarily evaluates the fetal heart rate response to movements of the fetus. This test is designed to monitor how the heart rate of the fetus responds when they move, which typically occurs when the baby is active. An increase in fetal heart rate with movement indicates that the fetus is getting adequate oxygen and is in good health, reflecting a well-functioning autonomic nervous system, which regulates heart rate.

The assessment is conducted by placing electrodes on the mother's abdomen to measure the fetal heart rate and recording it over a set period while also monitoring any fetal movements. This is a non-invasive procedure that provides valuable information about fetal well-being without causing stress to the mother or baby.

In context, the other options do not align with the purpose of the non-stress test. Evaluating maternal blood pressure response focuses on the mother's health status during pregnancy, which is not the primary goal of this test. Similarly, assessing maternal weight gain deals with nutritional and health considerations regarding the mother rather than the fetus. Lastly, measuring oxygen levels in the mother’s blood pertains to maternal respiratory function, which, while important, is outside the scope of what the non-stress test aims to measure.