One of the aspects of main importance on the determination of fertility is the insurance that marriage creates over a possible dissolution of the relationship. In this article, we present evidence that a greater level of insurance leads to a greater fertility. By analyzing the natural experiment given by the approval of the Cohabiting Law in December of 1994, we identify an increase on intentions of pregnancy by poor women directly affected by the Law. This increase is accompanied from a reduction on the probability that cohabiting women make a sterilization surgery. Our results are valid under many robustness checks.