When I learned that I was pregnant with my fourth child, I was very excited. My husband, children and I were living in Colorado, and it was the first winter that my mother was spending in Colorado, dividing her time between my crowded ranch in suburbia and my unmarried sister’s smaller but less crowded Tudor in Denver. Mom spent more of her time at the house in Denver, but she and my sister came to see me and the kids at least once a week. One week in January, I was especially looking forward to their visit, because I was…