Case-control genetic studies of Europeans have shown that pregnancy disorders that result from defective placentation with inadequate trophoblast arterial transformation (e.g., pre-eclampsia, fetal growth restriction, and recurrent miscarriage) are linked to an absence of the telomeric B (Tel-B) KIR region in the mother (Fig. 1A) and the presence of paternal C2 in the fetus (13, 18, 19). Here, KIR3DL1 is linked to pregnancy disorder.