How to tell whether a boy or girl is born on the pregnancy period chart. During the process of giving birth, many expectant parents hope to know whether their baby is a boy or a girl. This is very important to many people. However, many natural factors will affect the gender of the fetus, one of the most critical factors is the pregnancy cycle. Below we will give a detailed explanation on the topic of how the pregnancy cycle chart determines whether a boy or girl is born. 1. The concept and function of the pregnancy periodic table. The so-called pregnancy periodic table is a table calculated based on the date of conception and the expected date of delivery. It can help expectant mothers to have a rough idea.