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.
It's possible that nausea and vomiting during pregnancy might indicate that you're experiencing the normal climb in pregnancy hormones needed for a healthy pregnancy. However, high pregnancy hormone levels aren't consistently associated with nausea and vomiting. Keep in mind that a lack of nausea and vomiting during pregnancy isn't cause for concern. Some women with healthy pregnancies never experience morning sickness.