Final answer:
Superimposed pre-eclampsia is usually diagnosed after the 20th week of pregnancy in women with chronic hypertension who develop worsening hypertensive problems or proteinuria.
Step-by-step explanation:
Superimposed pre-eclampsia is typically diagnosed in the second half of pregnancy, often after the 20th week. This condition occurs in women who have chronic hypertension and then develop worsening hypertensive issues or proteinuria. Because the symptoms can closely resemble those of typical pre-eclampsia, differentiating superimposed pre-eclampsia from a chronic condition can be challenging. It is paramount for healthcare providers to monitor pregnant women with chronic hypertension closely for any changes that might indicate the development of superimposed pre-eclampsia.