**Core Concept**
Soft markers on ultrasonography refer to subtle, non-specific ultrasound findings that may indicate an increased risk of chromosomal or structural anomalies in the fetus. These markers are often identified during the second trimester and can be used in conjunction with other diagnostic tools to guide further testing or counseling.

**Why the Correct Answer is Right**
Soft markers on ultrasonography are helpful in diagnosing chromosomal anomalies because they can indicate an increased risk of conditions such as Down syndrome, trisomy 13, or trisomy 18. These markers may include features such as an increased nuchal translucency (NT) thickness, echogenic bowel, or short long bone. The presence of one or more soft markers can trigger further testing, such as amniocentesis or chorionic villus sampling (CVS), to confirm the diagnosis.

* **Option A:** Fetal age is typically determined using a combination of ultrasound measurements, including the crown-rump length (CRL) and biparietal diameter (BPD). While ultrasound can provide an estimate of gestational age, soft markers are not directly related to fetal age.
* **Option C:** Fetal size can be affected by various factors, including genetic conditions, but soft markers are not primarily used to diagnose growth restriction or macrosomia.
* **Option D:** The site of pregnancy can be determined using ultrasound, but soft markers are not related to the location of the pregnancy.

**Clinical Pearl / High-Yield Fact**
Soft markers on ultrasonography should not be used as a definitive diagnosis, but rather as a flag for further evaluation. The American College of Obstetricians and Gynecologists (ACOG) recommends that patients with soft markers undergo amniocentesis or CVS to confirm the diagnosis.

**✓ Correct Answer: B. Chromosomal anomalies.**