So it can come as quite a shock once you're postpartum to find that your big, bouncy hair is no more and is now thinning on a daily basis. Estrogen keeps hairs in their growth phase for longer and delays them from moving into their shedding phase–which means fuller, thicker, and glossier locks for you. Ever overheard a pregnant friend talking about how great her hair looks and feels? Well, changes in hair quality are just one of the many side effects of pregnancy–and for the most part, it's a very positive side effect! It's all to do with pregnancy hormones and the increase in estrogen in your body (a hair-friendly hormone).