Changes in the Endocrine system

Pituitary hormones of the pituitary gland -
  The secretion of prolactin, adenocorticotrophic hormone, thyrotrophic 
     hormone and melanocyte stimulating hormone increase follicle stimulating 
       hormone and leutinizing hormone secretion is greatly inhibited by placental 
         progesterone and estrogen. The posterior pituitary gland release oxytocin 
           in low frequencies pulses throughout pregnancy. At term, the frequency of 
              pulses increases which stimulate uterine contractions.

Thyroid gland -
   In the normal pregnancy the thyroid gland increases in size 
       by about 13% due to hyperplasia of glandular tissues and 
          increased vascularity. Rising level of T4 and T3 contribute 
             to the increased metabolic rate.

Adrenal gland - 
   The adrenal gland is stimulated by estrogen to produce increasing
      level of total and free plasma cortisol and other corticosteroids
        including ACTH from 12th week to term.