**Question:** A 26-year-old patient has had three consecutive spontaneous abortions early in the second trimester. As part of an evaluation for this problem, the least useful test would be

A. β-human chorionic gonadotropin (β-hCG) test
B. Thyroid Function Tests (TFTs)
C. Pelvic ultrasound
D. Complete blood count (CBC)

**Correct Answer:** D. Complete blood count (CBC)

**Core Concept:**

Spontaneous abortions, also known as miscarriages, occur when a pregnancy ends before the fetus reaches viability (24 weeks gestation). In this scenario, the patient has experienced three consecutive early second-trimester miscarriages, which raises suspicion for underlying maternal factors contributing to the problem.

**Why the Correct Answer is Right:**

Complete blood count (CBC) is a routine test that assesses the health of the patient by evaluating the number and type of blood cells. While it may provide some general health information, CBC is not specifically targeted towards evaluating potential causes of early second-trimester miscarriages.

**Why Each Wrong Option is Incorrect:**

A. β-human chorionic gonadotropin (β-hCG) test: β-hCG is a hormone secreted by the placenta, and its levels rise rapidly during pregnancy. A low or declining β-hCG level during pregnancy could indicate a miscarriage or ectopic pregnancy. Therefore, a β-hCG test is relevant and should not be considered the least useful test in this context.

B. Thyroid Function Tests (TFTs): TFTs assess thyroid function and are relevant to pregnancy complications when thyroid disorders are suspected. In this case, TFTs may be considered less useful than other tests as they are not specifically linked to miscarriage etiology.

C. Pelvic ultrasound: Ultrasound examination is essential in evaluating pregnancy complications, including assessing fetal viability, determining gestational age, and identifying ectopic or molar pregnancies. Assessing fetal heartbeat and viability is critical in evaluating pregnancy complications.

**Clinical Pearl:**

In the evaluation of recurrent miscarriages, a comprehensive approach involving detailed history, physical examination, and relevant investigations (such as β-hCG and transvaginal ultrasound) is essential to identify potential causes like antiphospholipid syndrome, chromosomal abnormalities, or uterine anomalies. Relying on a single test, like a CBC, may lead to missing important information required for correct diagnosis and management.