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All potentially clinically significant antibodies like this can be managed pretty well by non-invasive fetal monitoring for anemia by ultrasound (doppler velocity), so the management should be the same for all such antibodies. Clinical variation is great, as you all know, so the drill is to monitor the fetus. No anemia, no worries. Anemia leads to intervention. Serology is largely irrelevant (e.g., titers) but habit is to measure them by most clinicians.

There are a very few cases of severe HDFN caused by anti-Kpa (see references below). I believe that in many guidelines (to be confirmed though), antibodies to Kell blood group antigen are handled, by extrapolation, the same way as anti-K due to the very few examples reported in the literature. Costamagna L, Barbarini M, Viarengo GL, Pagani A, Isernia D, Salvaneschi L. A case of hemolytic disease of the newborn due to anti-Kpa. Immunohematology. 1997;13(2):61-2. PMID: 15387785. Tuson M, Hue-Roye K, Koval K, Imlay S, Desai R, Garg G, Kazem E, Stockman D, Hamilton J, Reid ME. Possible suppression of fetal erythropoiesis by the Kell blood group antibody anti-Kp(a). Immunohematology. 2011;27(2):58-60. PMID: 22356520. Smoleniec J, Anderson N, Poole G. Hydrops fetalis caused by a blood group antibody usually undetected in routine screening. Arch Dis Child Fetal Neonatal Ed. 1994 Nov;71(3):F216-7. doi: 10.1136/fn.71.3.f216. PMID: 7820722; PMCID: PMC1061131.

I do know of one case in the UK that involved an IUT given by Professor Kypros Nicolaides (a world renowned foetologist) at Kings College Hospital involving anti-Kpa in pregnancy, but I never saw it written up, and there was certainly no clinical sequalae, and so it could be that the anti-Kpa (the titre was not all that high) may well have been coincidental to some other pathological condition (KCH was one of "our" hospitals in terms of Red Cell Immunohaematology). In all my years in blood transfusion/blood group serology, I never saw an unequivocal case of anti-Kpa that caused clinically significant HDFN, and it was a fairly common antibody at our laboratory. That probably doesn't help that much, but that is my experience on the subject.