**Core Concept**
Non-stress test (NST) is a screening method used to assess fetal well-being by measuring fetal heart rate in response to fetal movement. It involves the use of a Doppler to detect fetal heart rate accelerations in response to fetal movement, providing an indirect assessment of fetal health.

**Why the Correct Answer is Right**
The non-stress test is considered the best initial screening method for fetal well-being because it is non-invasive, easy to perform, and free of risks associated with other methods. It measures the fetal heart rate in response to fetal movement, which is a reliable indicator of fetal health. The presence of two or more fetal heart rate accelerations within a 20-minute period indicates a normal fetal heart rate pattern.

**Why Each Wrong Option is Incorrect**
**Option A:** Contraction stress test (CST) is a more invasive method that measures fetal heart rate in response to uterine contractions, but it is not the best initial screening method due to its invasiveness and potential risks.
**Option B:** Biophysical profile (BPP) is a comprehensive assessment that includes ultrasound evaluation of fetal movement, tone, breathing, and amniotic fluid, but it is more expensive and time-consuming than the non-stress test.
**Option C:** Ultrasound biometry is used to measure fetal parameters such as biparietal diameter and abdominal circumference, but it does not provide information on fetal well-being.

**Clinical Pearl / High-Yield Fact**
The non-stress test is often used in conjunction with ultrasound biometry to provide a more comprehensive assessment of fetal well-being.

**Correct Answer: A. Non-stress test.