In this project there are 2 time points during the pregnancy included, namely at 21 weeks and 30 weeks of gestation, to measure the predictive values of FGR, strain and strain rate. The fetal growth parameters will be collected at the same time points, to define the growth (differences) throughout gestation of both fetuses. A maternal blood sample will be taken at 21 weeks of gestation to identify the level of exposure to air pollution (black carbon) and the level of biochemical markers of placental dysfunction. Doppler ultrasounds will be used for antenatal identification of placenta insufficiency. At birth, umbilical cord blood and the placenta will be collected. The placenta will be examined, to identify morphological findings which are associated with FGR. The umbilical cord blood and placental biopsy will be used for the level of exposure to air pollution and the level of oxidative stress. One to three days after birth, neonatal strain and strain rate will be measured to define postnatal cardiac remodeling as well as the neonatal blood pressure as cardiovascular risk factor.