Biological clock exists universally in all organisms. The mechanism of transcriptional translational oscillator loop is the main way of precise regulation of biological clock in mammals. The main part is made up of Clock, Bmal1, PER, CRY and so on. With the deep research of biological clock genes, it is found that the biological clock may be involved in a series of processes such as ovulation, embryo implantation, decidualization, and the maintenance of pregnancy. After pregnancy, the maternal biological clock genes will have corresponding changes to adapt to the pregnancy process. However, abnormal changes of biological clock may lead to pregnancy loss and pregnancy complications.

Biological clocks; Pregnancy; Spontaneous abortion; Pregnancy complications