5 Weeks Pregnant

Welcome to the official start of the embryonic period! For the first time since conception, baby’s rapidly multiplying cells are taking on specific functions—some are destined to become blood cells, while others will soon blossom into kidney or nerve cells. Baby’s major organs—including her brain, heart, and spinal cord—have started to develop, and her body is beginning to elongate. Baby may still be teeny-tiny—only a millimeter or so tall, in fact—but this is a monumental phase in her growth. This week and next, she’s most at risk from external factors that could cause birth defects, including excessive drinking, drug use, and certain medications.