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Performing amniocentesis in the third trimester is primarily aimed at testing for fetal lung maturity. This procedure allows healthcare providers to analyze the levels of surfactant in the amniotic fluid, which is a critical factor in assessing whether the fetus's lungs are sufficiently mature for breathing air outside the womb. Surfactant is produced by the alveoli in the lungs and prevents the collapse of the alveoli during exhalation, playing a vital role in respiratory function.

When a pregnancy is considered at risk for premature delivery, evaluating lung maturity helps guide clinical decisions regarding the timing of delivery. If fetal lungs are determined to be immature, medical interventions, such as administering corticosteroids to the mother, may be initiated to accelerate lung development and enhance outcomes for the baby at birth. Thus, the focus in the third trimester is often on the readiness of the fetus for life outside the uterus, making this the primary reason for amniocentesis during this period.

While genetic abnormalities and gender determination are relevant in earlier stages of pregnancy, they are not the main focus in the third trimester. Measurement of amniotic fluid volume also plays a role in assessing fetal health, but it is more commonly evaluated through ultrasounds rather than amnioc