Hormone changes after childbirth
BMJ Group Medical Reference
Hormones are chemicals that help to control how your body works. Pregnancy causes big changes in your hormones. These changes may have a role in postnatal depression.
The main changes are: 
Your level of a hormone called oestrogen rises to 50 times the normal level by the last three months of pregnancy. This is the main hormone made by your ovaries. Your oestrogen level falls back to normal in the three days after your baby is born
Your level of the hormone progesterone rises to 10 times the normal level when you're pregnant. Then it falls back to normal in the week after your baby is born
Your level of the hormone cortisol rises to two times to three times the normal level. Then it slowly decreases after birth
Your level of the hormone prolactin goes up to seven times its normal level when you are pregnant. This hormone helps your breasts make milk. The level drops back to normal in the three months after birth.
We don't know for certain if these hormone changes play a part in causing postnatal depression. But some women who get the illness may be more sensitive to these hormone changes than others. 
Hormones are chemicals that are made in certain parts of the body. They travel through the bloodstream and have an effect on other parts of the body. For example, the female sex hormone oestrogen is made in a woman's ovaries. Oestrogen has many different effects on a woman's body. It makes the breasts grow at puberty and helps control periods. It is also needed to get pregnant.
Women have two ovaries, one on each side of their womb. They are small glands that store eggs. Inside the ovaries are hundreds of thousands of pre-eggs, called follicles. Some of these grow into eggs.
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