At 3.5 weeks, the fetus will have formed the heart, begins development of the brain and spinal cord, and starts forming the gastrointestinal tract.
Review Date 8/26/2017
Updated by: Peter J Chen, MD, FACOG, Associate Professor of OBGYN at Cooper Medical School at Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.