We will conduct a clustered randomized controlled trial among pregnant women within an area of high transmission. The study participants will be recruited by the midwives in high risk areas, defined by postal code from the RIVM. To inform the public in this area about the study we will publish an article in local newspapers. The midwife centers will be randomized to recruit pregnant women for either the control group or the intervention group. The pregnant women will receive study information by mail using the midwives patients file. It is estimated that approximately 10,000 eligible women live in the areas of transmission. After written informed consent, they will start with the strategy for which the midwife center is randomized.