A 20-year-old woman, G3, P2, has a screening ultrasound at 18 weeks’ gestation that shows hydrops fetalis but no malformations. The woman’s two previous pregnancies ended at term in live births. The current pregnancy results in a live birth at 36 weeks. Physical examination shows marked hydrops of the neonate and placenta. Laboratory studies show a cord blood hemoglobin level of 9.2 g/dL and total bilirubin concentration of 20.2 mg/dL. Which of the following laboratory findings is most likely to be present in this case?

**Core Concept**
The underlying principle in this case is the diagnosis of a condition leading to fetal anemia and subsequent hydrops fetalis, which is a life-threatening condition characterized by the accumulation of fluid in two or more fetal compartments. This condition is often associated with severe anemia.

**Why the Correct Answer is Right**
The most likely diagnosis in this case is alpha-thalassemia major, also known as Hemoglobin Bart's hydrops fetalis syndrome. This condition occurs when a fetus inherits four copies of the alpha-globin gene deletion, leading to the production of abnormal hemoglobin (Hb Bart's). The accumulation of Hb Bart's in red blood cells results in severe anemia, which triggers the production of erythropoietin. In response, the fetus produces excess red blood cells, which accumulate fluid in various compartments, causing hydrops fetalis. The high levels of bilirubin in the cord blood are consistent with hemolysis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Elevated cord blood glucose levels would not be directly related to the pathophysiology of alpha-thalassemia major.
* **Option B:** A low cord blood creatinine level would not be expected in this condition, as the fetus is likely to have increased erythropoietin levels and subsequent renal effects.
* **Option C:** A low cord blood lactate level would not be expected in this condition, as the fetus is likely to have increased anaerobic metabolism due to severe anemia.

**Clinical Pearl / High-Yield Fact**
Alpha-thalassemia major is a severe form of alpha-thalassemia, and its diagnosis is often made prenatally by ultrasound. It is essential to recognize the clinical features of this condition to provide appropriate management and counseling for affected families.

**Correct Answer: D.**

✓ Correct Answer: C. Positive Coombs test result on cord blood