The Limburg Twin Study started in 2014 in the East-Limburg Hospital (ZOL) in Genk and will expand to the Belgium Province Limburg. The study is focusing on environmental effects during the pregnancy on growth and development of the child. Also the in utero effect of the environment on disease outcome later in life will be invested by measuring molecular parameters associated with ageing in cord blood and placenta tissue. The genetic background plays an important role in the susceptibility to these environmental factors. The advantage of twins is that they can provide insight in genetics in disease development.