三胚葉 always seems to correspond to "three germ layers" in translations of abstracts, articles, etc. from journals like Nature. It doesn't seem like there's a different English equivalent that is more widely used, if there is one at all.

Human oocytes reprogram somatic cells to a pluripotent state
このような胚盤胞から得られた幹細胞株は、三胚葉すべての細胞タイプへ分化し、体細胞由来のゲノムにおいて、多能性遺伝子発現プログラムが樹立される。
"Stem cell lines derived from these blastocysts differentiate into cell types of all three germ layers, and a pluripotent gene expression program is established on the genome derived from the somatic cell."

Transcription factor binding dynamics during human ES cell differentiation
本論文では、38個の転写因子について、ヒト胚性幹（ES）細胞の三胚葉への分化過程におけるゲノム全域での結合データと、広範なエピゲノムおよび転写のデータとの統合解析を報告する。
"Here we report the integrative analysis of genome-wide binding data for 38 transcription factors with extensive epigenome and transcriptional data across the differentiation of human embryonic stem cells to the three germ layers."

Generation of pluripotent stem cells from adult human testis
このヒト成体生殖系列幹細胞を、ヒト胚性幹細胞の分化誘導条件で増殖させると、三胚葉すべてのさまざまなタイプの体細胞に分化した。
"The human adult germline stem cells differentiated into various types of somatic cells of all three germ layers when grown under conditions used to induce the differentiation of human embryonic stem cells."

Rare simplicity
そのうえ、以前は間葉系腫瘍で見いだされていたEN産物が上皮悪性腫瘍でも見いだされたことから、この研究は融合遺伝子が三胚葉の1つにのみ結びつくという学説に挑むものである。
"Furthermore, this research challenges the dogma that fusion genes are only associated with one of the three germ layers, as the EN product has been previously found in mesenchymal tumours, and now in an epithelial malignancy."

Modelling pathogenesis and treatment of familial dysautonomia using patient-specific iPSCs
本論文では、患者特異的なFD-iPSCを誘導し、末梢ニューロンを含む三胚葉すべての細胞へ分化させることができたので報告する。
"Here we report the derivation of patient-specific FD-iPSCs and the directed differentiation into cells of all three germ layers including peripheral neurons."

Resolving early mesoderm diversification through single-cell expression profiling
哺乳類では、原腸形成期に主要な三胚葉の指定が起こり、このとき原条へ移入する細胞が主要な器官系の前駆細胞へ分化する。
"In mammals, specification of the three major germ layers occurs during gastrulation, when cells ingressing through the primitive streak differentiate into the precursor cells of major organ systems."

Derivation and differentiation of haploid human embryonic stem cells
意外にも、半数体ヒトゲノムは常染色体とX染色体の遺伝子量が絶えず不均衡であるにもかかわらず、未分化の多能性状態に適合するだけでなく、in vitroおよびin vivoにおいて胚性の三胚葉の全てを代表する分化した体細胞運命にも適合することが分かった。
"Surprisingly, we found that a haploid human genome is compatible not only with the undifferentiated pluripotent state, but also with differentiated somatic fates representing all three embryonic germ layers both in vitro and in vivo, despite a persistent dosage imbalance between the autosomes and X chromosome."

I linked another example as a web reference because I think it's the only one you don't need to be logged in to see.