Option 1: Eradicate extreme poverty is indeed one of the Millennium Development Goals (MDGs) of the United Nations (UN). The goal is to reduce the number of people living in extreme poverty by half.

Option 2: Reduce birthrate and death rate is not a Millennium Development Goal. The actual goal related to this aspect is to reduce child mortality, which is covered under MDG 4.

Option 3: Improve maternal health is one of the MDGs. The aim is to reduce maternal mortality and ensure access to reproductive health services for women.

Option 4: Promote gender equality is also one of the MDGs. The goal is to eliminate gender disparities in education and empower women.

In conclusion, by process of elimination, option 2 - Reduce birthrate and death rate, is the correct answer as it does not correspond to any of the Millennium Development Goals defined by the United Nations.