A paediatrician measures the head of Linda Abigail, the third child of Lourdes Suyapa Rodriguez, 35, after she was born at 00:20 in the childbirth unit of the Escuela hospital in Tegucigalpa October 31, 2011. The world?s population will reach seven billion on 31 October 2011, according to projections by the United Nations, which says this global milestone presents both an opportunity and a challenge for the planet. While more people are living longer and healthier lives, says the U.N., gaps between rich and poor are widening and more people than ever are vulnerable to food insecurity and water shortages. REUTERS/Edgard Garrido (HONDURAS - Tags: HEALTH SOCIETY)