Relationship between obstetric history and Rh(D) alloimmunization severity

Effect of Anti-D titers in RhD-negative pregnant women on fetuses and newborns: A retrospective study

BACKGROUND

Transplacental-derived anti-D IgG in RhD-negative pregnant women can trigger an immune response to Rh D-positive red cells in fetuses and newborns. We assessed the effect of anti-D titers in RhD-negative pregnant women on fetuses and newborns.

METHODS

The clinical data of 142 singleton RhD-sensitized pregnancies were retrospectively collected. The pregnant women received routine prenatal care and the newborns had standard care. Based on the tertile categories of the pregnancies, the maximum titers of anti-D IgG in the pregnant women were divided into three groups ranging from low to high as follows: low-titer group (anti-D titer: 1:4-1:128, n = 57); medium-titer group (anti-D titer: 1:256-1:512, n = 50); and high-titer group (anti-D titer: 1:1024-1:4096, n = 35).

RESULTS

The frequencies of major neonatal complications did not significantly differ among the three groups. The high-titer group had the highest frequency of pregnancies requiring intrauterine transfusion (IUT) and number of IUTs among the three groups. The high-titer group had a significantly higher frequency of newborns treated with top-up transfusion, number of top-up transfusions, frequency of newborns treated with exchange transfusion (ET), and number of ETs when compared to the low-titer group.

CONCLUSION

Higher anti-D titers in RhD-negative pregnant women predict more severe fetal and neonatal hemolytic anemia. Increasing maternal anti-D titers results in an increased need for IUTs, and neonatal top-up transfusions and ETs. Methods for reducing titers of anti-D IgG in RhD-sensitized pregnant women warrants further investigation.

Fetal and neonatal bilirubin metabolism

Human fetal and neonatal bilirubin metabolism is centered on 4Z,15Z-bilirubin IXα (BR) due to the extremely low BR conjugating capacity of the liver. BR is a unique, highly lipophilic substance with physiological and toxic effects in the cell membranes of organs and body tissues. The fetus excretes BR through the placenta to the maternal circulation. After birth, BR is thought to act as an antioxidant against the increase in reactive oxygen species caused by the rapid increase in oxygen concentration during the adaptation process from in amniotic fluid to in air. However, bilirubin encephalopathy is a toxic effect of bilirubin. Due to the lipophilic nature of BR, it must be bound to a carrier to be distributed to various parts of the body by hydrophilic blood. This carrier of BR is human serum albumin (HSA). In humans, BR can be excreted efficiently after undergoing photochemical reactions upon high affinity binding to HSA. HSA also plays an important role in the prevention of bilirubin encephalopathy. This review focuses on the developmental and physiological role of bilirubin metabolism during the fetal and neonatal periods.

No. 394-Stillbirth Investigation

OBJECTIVES

To provide an investigation protocol to help health care providers determine the cause of a fetal death.

OPTIONS

Consideration has been given to protocols for the investigation of fetal death that are currently available in Canada and in other countries.

OUTCOMES

Identification of possible causes of stillbirth and their relationship to future pregnancies.

EVIDENCE

Articles related to the etiology of fetal death were identified in a search of PubMed (June 2006 to September 2018), the Cochrane Library, and investigation protocols from the American College of Obstetricians and Gynecologists, the International Stillbirth Alliance Collaborative for Improving Classification of Perinatal Deaths, the Royal College of Obstetricians and Gynaecologists, the Queensland clinical guidelines, and the Reproductive Care Program of Nova Scotia.

BENEFITS

To provide better advice for women regarding possible causes of fetal death and implications for future pregnancies.

VALIDATION

The evidence obtained was reviewed and evaluated by the Maternal-Fetal Medicine Committee and the Clinical Practice Obstetrics Committee of the Society of Obstetricians and Gynaecologists of Canada. The level of evidence and quality of the recommendation made was described using the Evaluation of Evidence criteria of the Canadian Task Force on Preventive Health Care.

RECOMMENDATIONS

Predicting Intrauterine Transfusion Interval and Perinatal Outcomes in Alloimmunized Pregnancies: Time-to-Event Survival Analysis

BACKGROUND

The risk factors determining the frequency of intrauterine transfusions (IUTs) for severely affected red blood cell alloimmunized singleton pregnancies are not well known.

OBJECTIVE

To assess factors associated with IUT frequency and adverse pregnancy outcomes in transfused pregnancies.

METHODS

Retrospective cohort analysis of 246 consecutive cases between 1991 and 2014. Time-to-event survival analysis for repeated events was used to evaluate risk of subsequent IUT. Multivariable logistic regression assessed odds of a composite adverse pregnancy outcome (intrauterine fetal death, termination of pregnancy, neonatal death, preterm birth <34 weeks' gestation).

RESULTS

Full information was available on232 cases (94.3%) and 716 IUTs. Fetal hydrops was associated with increased frequency (hazard ratio [HR] 1.29 [95% CIs 1.15-1.47, p < 0.001]) while higher fetal hemoglobin (Hb) pre-IUT (HR) 0.99 (95% CI 0.99-1.00, p = 0.021) and post-IUT (HR 0.99 [95% CI 0.99-1.00] p = 0.042), and higher transfused blood volume (HR 0.98 [95% CI 0.97-0.99] p < 0.001) were associated with reduced IUT frequency. Adverse pregnancy outcomes were more likely with lower gestational age (GA) at initial IUT. Antibody type was not associated with IUT frequency or adverse pregnancy outcomes.

CONCLUSIONS

Hydrops is associated with increased IUT frequency while lower GA at initial IUT is associated with higher adverse pregnancy outcomes in alloimmunized pregnancies.Higher transfused blood volumes, pre- and post-IUT Hb are associated with lower IUT frequency.

M281, an anti-FcRn antibody, inhibits IgG transfer in a human ex vivo placental perfusion model

BACKGROUND

The transfer of pathogenic immunoglobulin G antibodies from mother to fetus is a critical step in the pathophysiology of alloimmune and autoimmune diseases of the fetus and neonate. Immunoglobulin G transfer across the human placenta to the fetus is mediated by the neonatal Fc receptor, and blockade of the neonatal Fc receptor may provide a therapeutic strategy to prevent or minimize pathological events associated with immune-mediated diseases of pregnancy. M281 is a fully human, aglycosylated monoclonal immunoglobulin G1 antineonatal Fc receptor antibody that has been shown to block the neonatal Fc receptor with high affinity in nonclinical studies and in a phase 1 study in healthy volunteers.

OBJECTIVE

The objective of the study was to determine the transplacental transfer of M281 and its potential to inhibit transfer of immunoglobulin G from maternal to fetal circulation.

STUDY DESIGN

To determine the concentration of M281 required for rapid cellular uptake and complete saturation of the neonatal Fc receptor in placental trophoblasts, primary human villous trophoblasts were incubated with various concentrations of M281 in a receptor occupancy assay. The placental transfer of M281, immunoglobulin G, and immunoglobulin G in the presence of M281 was studied using the dually perfused human placental lobule model. Immunoglobulin G transfer was established using a representative immunoglobulin G molecule, adalimumab, a human immunoglobulin G1 monoclonal antibody, at a concentration of 270 μg/mL. Inhibition of immunoglobulin G transfer by M281 was determined by cotransfusing 270 μg/mL of adalimumab with 10 μg/mL or 300 μg/mL of M281. Concentrations of adalimumab and M281 in sample aliquots from maternal and fetal circuits were analyzed using a sandwich enzyme-linked immunosorbent assay and Meso Scale Discovery assay, respectively.

RESULTS

In primary human villous trophoblasts, the saturation of the neonatal Fc receptor by M281 was observed within 30-60 minutes at 0.15-5.0 μg/mL, suggesting rapid blockade of neonatal Fc receptor in placental cells. The transfer rate of adalimumab (0.23% ± 0.21%) across dually perfused human placental lobule was significantly decreased by 10 μg/mL and 300 μg/mL of M281 to 0.07 ± 0.01% and 0.06 ± 0.01%, respectively. Furthermore, the transfer rate of M281 was 0.002% ± 0.02%, approximately 100-fold lower than that of adalimumab.

CONCLUSION

The significant inhibition of immunoglobulin G transfer across the human placental lobule by M281 and the minimal transfer of M281 supports the development of M281 as a novel agent for the treatment of fetal and neonatal diseases caused by transplacental transfer of alloimmune and autoimmune pathogenic immunoglobulin G antibodies.