The commonest congenital anomaly seen in pregnancy with diabetes mellitus is:
**Core Concept**
The question is testing the association between maternal diabetes mellitus and congenital anomalies in the fetus. Maternal diabetes mellitus is known to increase the risk of congenital anomalies due to hyperglycemia and subsequent teratogenic effects.
**Why the Correct Answer is Right**
The commonest congenital anomaly seen in pregnancy with diabetes mellitus is cardiac defects, specifically ventricular and atrial septal defects. This is due to the teratogenic effect of hyperglycemia on the developing heart, which is particularly susceptible during the first trimester. The increased glucose levels lead to increased insulin production, which in turn stimulates the growth of the heart and other tissues, resulting in defects.
**Why Each Wrong Option is Incorrect**
**Option A:** Neural tube defects are indeed associated with diabetes mellitus, but they are not the most common congenital anomaly. Neural tube defects are thought to occur due to the teratogenic effects of hyperglycemia on the neural tube, but they are less common than cardiac defects.
**Option B:** Renal anomalies are also associated with diabetes mellitus, but they are not the most common congenital anomaly. Renal anomalies are thought to occur due to the teratogenic effects of hyperglycemia on the developing kidneys.
**Option C:** Limb reduction defects are not commonly associated with diabetes mellitus. Limb reduction defects are thought to occur due to vascular compromise or other teratogenic effects.
**Clinical Pearl / High-Yield Fact**
It is essential to screen pregnant women with diabetes mellitus for congenital anomalies, particularly cardiac defects, using ultrasound and other diagnostic tests.
**Correct Answer: C. Cardiac defects, specifically ventricular and atrial septal defects.**