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.
Similarly, estrogen, another hormone that increases during pregnancy, is associated with an increased frequency of nausea and vomiting during pregnancy. 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.