| Value | Category | 
                                    
                    
                        | 1 | Women at risk only | 
                                    
                    
                        | 2 | First visit only | 
                                    
                    
                        | 3 | Some visits | 
                                    
                    
                        | 4 | Every visit | 
                                    
                    
                        | 5 | Never | 
                                    
                    
                        | Sysmiss |  | 
                            
            Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.