**Core Concept**
Pregnancy increases the risk of urinary tract infections (UTIs) due to physiological changes such as ureteral dilatation and decreased bladder sensation. The presence of leucocyte esterase and a high colony count of E. coli in urine suggests an asymptomatic bacteriuria (ASB) in this patient.

**Why the Correct Answer is Right**
Asymptomatic bacteriuria is defined as the presence of more than 100,000 colony-forming units (CFU) of a single pathogen per milliliter of urine in a person without symptoms of a urinary tract infection. In pregnancy, ASB is a significant concern as it can lead to pyelonephritis, a potentially life-threatening complication. The patient's lack of urinary symptoms does not rule out the presence of ASB.

**Why Each Wrong Option is Incorrect**
**Option A:** ASB is indeed associated with an increased risk of pyelonephritis in pregnancy, so this statement is true.
**Option C:** The presence of E. coli in the urine is a common cause of ASB, so this statement is true.
**Option D:** The patient's urine culture showing E. coli > 100,000 organisms/mL confirms the presence of ASB, so this statement is true.

**Clinical Pearl / High-Yield Fact**
Asymptomatic bacteriuria in pregnancy requires prompt treatment with antibiotics to prevent pyelonephritis and other complications.

**Correct Answer: B.**