T cells, which are one type of white blood cell in the immune system, somehow become sensitized to proteins in the CNS. When T cells become activated, they enter the CNS through blood vessels and produce damaging inflammation.
1 Fatigue or Tiredness: Feeling fatigued or more tired than usual, is a pregnancy symptom which can also start as early as the first week after conception.  Morning Sickness or Nausea: This well-known pregnancy symptom will oftentimes show up between 2-8 weeks after conception.
According to Dr. Marjorie Greenfield, ob-gyn and author of The Working Woman's Pregnancy Book, approximately 70 percent of women experience nausea early in pregnancy and about 50 percent experience vomiting. It's very, very common, but it's also incredibly varied, Greenfield says.