Frequency and characterization of known and novel RHD variant alleles in 37 782 Dutch D-negative pregnant women.

To guide anti-D prophylaxis, Dutch D- pregnant women are offered a quantitative fetal-RHD-genotyping assay to determine the RHD status of their fetus. This allowed us to determine the frequency of different maternal RHD variants in 37 782 serologically D- pregnant women. A variant allele is present in at least 0·96% of Dutch D- pregnant women The D- serology could be confirmed after further serological testing in only 54% of these women, which emphasizes the potential relevance of genotyping of blood donors. 43 different RHD variant alleles were detected, including 15 novel alleles (11 null-, 2 partial D- and 2 DEL-alleles). Of those novel null alleles, one allele contained a single missense mutation (RHD*443C>G) and one allele had a single amino acid deletion (RHD*424_426del). The D- phenotype was confirmed by transduction of human D- erythroblasts, consolidating that, for the first time, a single amino acid change or deletion causes the D- phenotype. Transduction also confirmed the phenotypes for the two new variant DEL-alleles (RHD*721A>C and RHD*884T>C) and the novel partial RHD*492C>A allele. Notably, in three additional cases the DEL phenotype was observed but sequencing of the coding sequence, flanking introns and promoter region revealed an apparently wild-type RHD allele without mutations.

Fetal RHD genotyping after bone marrow transplantation.

BACKGROUND: Fetal RHD genotyping allows targeted diagnostic testing, fetal surveillance, and eventually intrauterine treatment to D-alloimmunized pregnant women who carry an RHD+ fetus. However, false-positive and false-negative results of noninvasive prenatal fetal RHD genotyping have been described due to a variety of causes. In this case report we present two cases where noninvasive fetal RHD typing was complicated by a previous bone marrow transplantation (BMT). CASE REPORT: We describe two women with a history of allogeneic BMT in early childhood. Both were born D+ and received a transplant of their D- male sibling. Anti-D were detected during pregnancy in one of them. The biologic father of this pregnancy was D+. In both cases polymerase chain reaction procedures specific for RHD on maternal plasma DNA were positive whereas a D- neonate was born in one case (Case 1). CONCLUSION: False-positive results of noninvasive fetal RHD genotyping occur in D+ women transplanted with marrow of a D- donor, due to circulating cell-free DNA originating from nonhematopoietic tissue. The cases highlight that health care professionals and laboratories should be aware that allogeneic BMT can be a cause for false-positive results in fetal RHD genotyping with cell-free DNA in maternal plasma, and likewise the wrong fetal sex can be reported in the case of a male donor and a female fetus. Based on one of the cases we also recommend giving D- blood products to young female patients who receive a BMT of D- donors.

Absolute first trimester cell-free DNA levels and their associations with adverse pregnancy outcomes.

OBJECTIVE: To study associations of first trimester cell-free fetal DNA levels (in this paper referred to as cell-free placental DNA (cfpDNA) levels) and preeclampsia (PE), pregnancy-induced hypertension (PIH), gestational diabetes (GDM) and spontaneous preterm birth (sPB). METHOD: A nested case-control study was conducted in first trimester samples (gestational age 8+0 -13+6 weeks). A total of 226 cases and 301 controls were included. CfpDNA levels were quantified in male-bearing pregnancies using real-time DYS14-PCRs on DNA isolated from maternal serum. CfpDNA multiples of the median (MoMs) were calculated based on associations with patient characteristics (body mass index, parity, ethnicity and smoking). Associations between MoMs and adverse outcomes were studied. RESULTS: Cell-free placental DNA levels were negatively associated with body mass index (ß = -0.297, p < 0.001) and smoking (ß = -0.163, p = 0.006). MoMs were lower in women who later developed PIH (n = 84, p = 0.009) or GDM (n = 56, p = 0.037). There was no association between cfpDNA MoMs and PE (n = 37, p = 0.15) or sPB (n = 49, p = 0.19). CfpDNA was positively correlated with pregnancy-associated plasma protein A (r = 0.426, p < 0.001) but not with placental growth factor (r = 0.059, p = 0.179). CONCLUSION: Adjusted first trimester cfpDNA levels are associated with PIH and GDM but probably not with PE or sPB. © 2016 John Wiley & Sons, Ltd.

Sensitivity of fetal RHD screening for safe guidance of targeted anti-D immunoglobulin prophylaxis: prospective cohort study of a nationwide programme in the Netherlands.

OBJECTIVE:  To determine the accuracy of non-invasive fetal testing for the RHD gene in week 27 of pregnancy as part of an antenatal screening programme to restrict anti-D immunoglobulin use to women carrying a child positive for RHD DESIGN:  Prospectively monitoring of fetal RHD testing accuracy compared with serological cord blood typing on introduction of the test. Fetal RHD testing was performed with a duplex real time quantitative polymerase chain reaction, with cell-free fetal DNA isolated from 1 mL of maternal plasma The study period was between 4 July 2011 and 7 October 2012. The proportion of women participating in screening was determined. SETTING:  Nationwide screening programme, the Netherlands. Tests are performed in a centralised setting. PARTICIPANTS:  25 789 RhD negative pregnant women. MAIN OUTCOME MEASURES:  Sensitivity, specificity, false negative rate, and false positive rate of fetal RHD testing compared with serological cord blood typing; proportion of technical failures; and compliance to the screening programme. RESULTS:  A fetal RHD test result and serological cord blood result were available for 25 789 pregnancies. Sensitivity for detection of fetal RHD was 99.94% (95% confidence interval 99.89% to 99.97%) and specificity was 97.74% (97.43% to 98.02%). Nine false negative results for fetal RHD testing were registered (0.03%, 95% confidence interval 0.01% to 0.06%). In two cases these were due to technical failures. False positive fetal RHD testing results were registered for 225 samples (0.87%, 0.76% to 0.99%). Weak RhD expression was shown in 22 of these cases, justifying anti-D immunoglobulin use. The negative and positive predictive values were 99.91% (95% confidence interval 99.82% to 99.95%) and 98.60% (98.40% to 98.77%), respectively. More than 98% of the women participated in the screening programme. CONCLUSIONS:  Fetal RHD testing in week 27 of pregnancy as part of a national antenatal screening programme is highly reliable and can be used to target both antenatal and postnatal anti-D immunoglobulin use.