Around the world, women are having far fewer children than they were 50 years ago. This decline in fertility threatens to cause falling populations in many countries, which weighs on economic growth because it means fewer workers who can produce goods and services. In the first of a two-part episode of Benchmark, Scott Lanman talks with Elizabeth Katkin, author of the new book "Conceivability," about why it's so hard for many couples to overcome struggles with fertility -- and how countries differ on their approach to the issue.