Urinary Tract Infection (UTI): Given the sharp, seconds-long bladder pain, a UTI is a common condition in pregnancy, especially in the late third trimester, due to urinary stasis and ureteral dilation. The pain can be severe and fleeting.

Kidney Stones: Although less common in pregnancy, kidney stones can cause severe, sharp pain that can be mistaken for bladder pain. The pain can be intermittent and may radiate to the groin.
Overdistended Bladder: In the late third trimester, the enlarged uterus can put pressure on the bladder, leading to overdistension and sharp pain, especially if the patient has not voided recently.
Braxton Hicks Contractions: While typically felt as abdominal tightening, Braxton Hicks contractions can sometimes cause pressure on the bladder, leading to sharp, transient pain.

Placental Abruption: Although the primary symptom is vaginal bleeding, placental abruption can cause severe abdominal pain that might be referred to the bladder area. It's a life-threatening condition that requires immediate attention.
Preterm Labor: Sharp pain could be a symptom of preterm labor, especially if accompanied by regular uterine contractions. It's crucial to differentiate this from other causes of pain to ensure appropriate management.
Ureteral Obstruction: Obstruction of a ureter, which could be due to a stone or the pregnant uterus compressing the ureter, can cause severe, sharp pain. This condition requires prompt diagnosis and treatment to prevent long-term kidney damage.

Interstitial Cystitis: A chronic condition that can cause bladder pain, but it's less likely to present acutely in the late third trimester without a previous history.
Bladder Cancer: Extremely rare in pregnancy and even more so in younger populations, but could potentially cause sharp bladder pain if a tumor is present.