At approximately day 1

Thyroglobulin present in fetal serum.

Reference [PubMed Link]

Howdeshell KL. 2002. A model of the development of the brain as a construct of the thyroid system. Environ Health Perspect 110 (suppl 3):337-348.

At approximately day 1

Serum thyroxine, thyroid-stimulating hormone and thyroxine-binding globulin detected.

Reference [PubMed Link]

Greenberg AH, Czernichow P, Reba RC, Tyson J, Blizzard RM. 1970 Oct. Observations on the maturation of thyroid function in early fetal life. J Clin Invest 49(10):1790-803.

At approximately day 1

Somatotropes (which produce GH) present.

Reference [PubMed Link]

Sadler TW. 2000. Susceptible periods during embryogenesis of the heart and endocrine glands. Environ Health Perspect 108 (suppl 3):555-561.

At approximately day 4

Portal system to pituitary established.

Reference [PubMed Link]

Thliveris JA, Currie RW. 1980. Observations on the hypothalamo-hypophyseal portal vasculature in the developing human fetus. Am J Anat 157(4):441-444.