A light brown period after fertility treatment can happen for several reasons and is usually not a cause for serious concern. Brown discharge often means old blood that is taking longer to leave the uterus (womb). In your case, medicines like Fertomid and hormonal injections used to support egg growth can affect your natural hormone balance, which may slightly delay your period or make the bleeding lighter than usual. If the lining of the uterus is thinner, like 5.6 mm in your report, there is less tissue to shed, so the flow can become very light or appear only as spotting instead of a normal period. It is also normal for the cycle to shift by a few days after treatment, which can explain why your period came on day 30 instead of day 26. Since the pregnancy test is negative, pregnancy is unlikely. These changes can also be influenced by stress and how your body responds to the medicines. If this pattern continues in future cycles, it is best to follow up with your doctor.