Anti‐Kell in pregnancy

Dear Sir, We read with interest the recent paper detailing the Newcastlc series of women with anti-Kell antibodies by Leggatetal., [BrJObstet Gynaecol (1991)98,162-1651, but found thisat almosttotal variance with our experience. As stated in the paper, Kell is an uncommon antibody, only 10-15% of the population being Kcll positive with most women developing antibodies following a blood transfusion. Thus only 1U-15% of women with antibodies will have a partner who is Kell positive and as most of these will be heterozygous, only approximately 50% will have a Kell positive fetus. Stated another way. for every 100 women with anti-Kell antibodies only a maximum seven will be in a position to have even a mildly affected fetus. The prognosis for this 7% will. however, be vastly different to the other 93%. Although this paper discusses the value of knowing the genotype of the partner, neither this nor the antenataVpostnata1 genotype of the fetus ismentionedin theresults. Bothofthese arecritical to the correct management of the condition, and without them the contents of Table 1 are almost mcaningless as statistically only around 14/194 will have a Kell positive fetus. It should thus come as no surprise that four women with titres of 112048 would have unaffectcd fetuses. Neither are any intrauterine treatments or the gestation at delivery mentioned. During 19W we were involved in the management of 10 women with anti-Kell antibodies, four of these had a Kell positive fetus and none of them had had a previous affected pregnancy. All these women had titres reported as high or very high. One other woman underwent a cordocentesis and was found to have a Kell negative fetus. Two of the women were inappropriately managed by the referring general practitioner or consultantwhofailed to appreciate theimportance of the condition and the rate at which deterioration can occur. Both of these women had polyhydramnios and the fetuses had markedascites togetherwithscalp oedema in one. We have previously managed another similar woman whose fetus had ascites and a pericardial effusion. This contrasts with no such fetuses over 25 years in Newcastle. All thrcc fetuses became hydropic before 30 wecks gestation and in all of them the amniotic fluid A OD values werc totally misleading being within the Liley midzone, i.e., false negatives as rcported previously (Caine & Mueller-Heubach 1986). We find it difficult to explain the apparent occurrence of serious false positives described from Newcastle, and indeed no explanation is forthcoming in their discussion. Ofourfouraffectcdfetuses, one hadfourintrauterine transfusions and was safely born at 35 weeks, and another had one transfusion and was born 3 weeks later following an abruption. The lowest haematocrit in these two fetuses was 18 and 21% respectively. The third fetus was the most severely affected and was immediately delivered, and the babysurvived. Theoutcome in the fourth affected fetus illustrates the unpredictability of the condition. The mother had a high level of anti-Kell antibodies with a positive partner. Cordocentesis showed the fetus to be Kell positive but with a negative direct Coombs test. No treatment was required antenatally, the results were confirmed after birth, but the baby required phototherapy. We would agree that anti-Kell antibodies are extremely unpredictable and cannot be assessed using the same methods as described for anti-D such as amniocentesis and optical density measurements, but we cannot agree that the condition with a Kell positive fetus is as benign as the paper implies and a thorough understanding of the importance of this condition and its unpredictability is vital to all who deal with pregnant women. A simple protocol should be followed in all such pregnancies (i) Check the Kell status of the partner. If negative treat as a normal pregnancy and ignore antibodies. (ii) If partner is Kell positive refer for cordocentesis after 20 weeks. If the fetus is negative treat as a normal pregnancy and ignore antibodies. (iii) If the fetus is Kell positive refer for management and treatment at a centre dealing with this problem regularly, where cordo-