The hairs on your body grow in a cycle, which consists of different phases: the growth phase, the transition phase, the resting phase and the shedding phase. The growth phase lasts the longest, which is why most hairs are firmly anchored. Approximately 50 to 100 hairs fall out daily, with new hairs growing in their place. One of the factors that influence your hair growth is hormones. During pregnancy, the composition of hormones in your body changes, which also affects your hair. Due to the prolonged high levels of estrogen, your scalp hair remains in the resting phase. Therefore, it does not fall out, resulting in that thick head of hair when you are pregnant.