Aggregate of cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta. They are formed during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg. [Wikipedia:Trophoblast]

http://purl.obolibrary.org/obo/Blastocyst_English.svg

The postimplantation derivatives of the trophectoderm, which make up most of the fetal part of the placenta

the mesectodermal cell layer arising from the trophectoderm that erodes the uterine mucosa and contributes to the formation of the placenta[MP]

uberon

trophoblastus, trophoderm, massa cellularis externa

trophoblastic

UBERON:0000088

• blastocyst

• inner cell mass