Pregnancy process	Factors expressed or produced by uNK cells	Function	References
Implantation	Prokinetincin1 (a marker of receptive endometrium) secreted by uNK cells	Facilitating the embryo to implant into the endometrium by regulating implantation factor like leukemia inhibitory factor, IL-11, and prostaglandins	[50] [51] .
Implantation	High expression of KIR2DL4	Activating a pro-inflammatory/proangiogenic response by binding with its ligand HLAG on trophoblastic cells; this step is beneficial to the establishment of receptive endometrium	[48]
Decasualization	IL-25 secreted by dNK cells	Promotes the proliferation of DSCs and of the regulation of decasualization	[53]
Decasualization	Killer immunoglobulin-like receptors	Control NK cell activity and cytotoxicity	[18]
Placentation	IL-8 and INF-γ inducible protein, IP10	Increasing MMP-9 secretion, which reduces the apoptosis of extra villus trophoblastic cells (EVT)	[62]
Placentation	TNF-α, TGF-β and IFN-γ	Down-regulate the harmful excessive EVT invasion	[62] [63]
Spiral arteries remodeling	IL-8, TGF-β, angiopoietin-1/2 (Ang1/2), and VEGF-C	Contribute to increase the calibers diameter of spiral arteries to maintain satisfactory blood flow to the growing Festus	[60] [66] [67]
Fetal development	dNK cells secrete growth-promoting factors like pleiotrophin (PTN)and osteoglycin (OGN)	Promote the growth and development of the fetus	[70]