One theory is that female hormones (like estrogen) might play an important role in causing OCD, which could put women at higher risk during puberty and after having babies. About one-quarter of women with OCD say their symptoms started when they got their first period, when hormone levels change dramatically. A large review study found that 1.08% of women in the general population develop OCD after having a baby, compared to 2.07% during pregnancy and 2.43% right after giving birth. The analysis showed that pregnant women and new mothers are 1.5 to 2 times more likely to develop OCD than other women. An animal study found that female rats had trouble overcoming their fears when their hormone levels were low during their reproductive cycle.