How is BBT connected to pregnancy?

Progesterone stays risen and then increases during pregnancy. Progesterone prevents the uterine lining from shedding or otherwise repelling the newly fertilized egg. In the first 10 – 12 weeks, the corpus luteum continues to provide the progesterone your body needs. After this stage the placenta develops and takes over as the source of progesterone. Progesterone acts on the thyroid to keep your basal body temperature high during pregnancy at around 98 °F.