nidation Female 50 female 50 Pregnancy 44 controlled study 40 human 36 pregnancy 36 priority journal 36 Animals 30 Embryo Implantation 30 Humans 30 article 30 nonhuman 28 metabolism 26 trophoblast 26 animal experiment 20 mouse 20 protein expression 20 Mice 18 Trophoblasts 18 Uterus 16 animal tissue 16 gene expression 16 human cell 16 in vitro study 16 Placenta 14 Vasoactive Intestinal Peptide 14 cell proliferation 14 leptin 14 signal transduction 14