An elevated fetal interleukin-6 concentration can be observed in fetuses with anemia due to Rh alloimmunization: implications for the understanding of the fetal inflammatory response syndrome

Figures & data

Table I.  Demographic and clinical characteristics of the study population.

Variable	No fetal anemia (n = 6)	Fetal anemia (n = 10)	p
Maternal age (years)	36 (31.5–39)	35 (30.7–36.2)	0.4
Ethnic origin – Hispanic	100 (6)	100 (10)	1
Smoking	50 (3)	0 (0)	0.04
Prepregnancy BMI (kg/m^2)	26.7 (23.3–30.1)	25.3 (22.7–27.6)	0.5
Gestational age at sampling (weeks)	29.9 (28.2–32.7)	30.8 (27.7–32.6)	1.0
Gestational age at delivery (weeks)	35.8 (33.5–36.3)	35.4 (33.5–35.9)	0.6
Birthweight (g)	2550 (2167–2892)	2620 (2337–2925)	0.9

Values are expressed as median (interquartile range) or percent (number).

BMI, body mass index.

Figure 1.  Correlation between fetal hematocrit and plasma IL-6 concentration among 16 fetuses with Rh alloimmunization who underwent cordocentesis for suspected anemia. There was a significant negative correlation between the fetal hematocrit and plasma IL-6 concentration (Spearman's rho −0.68, p = 0.004). The interrupted line represents the cutoff value of IL-6 concentration for the diagnosis of FIRS. Four fetuses (‘empty’ dots) were diagnosed with FIRS.

Figure 2.  Comparison of fetal plasma concentration of IL-6 between fetuses with anemia and those without anemia. The median fetal plasma IL-6 concentration was higher in fetuses with anemia than that of those without anemia (3.74 pg/ml, interquartile range (IQR) 1.79–14.7 vs. 1.46 pg/ml, IQR 1.18–2.63; p = 0.02). The interrupted line represents the cutoff value of IL-6 concentration for the diagnosis of FIRS. All fetuses with FIRS had anemia (‘empty’ dots).

Figure 3.  Comparison of amniotic fluid concentration of IL-6 between fetuses with anemia and those without anemia. The median amniotic fluid IL-6 concentration was not significantly different between women with anemic fetuses and those with fetuses without anemia (anemia: 1089 pg/ml, interquartile range (IQR) 542–2009 vs. no anemia: 471.5 pg/ml, IQR 357–693; p = 0.06). Intra-amniotic inflammation was diagnosed in only one fetus with FIRS. The interrupted line represents the cutoff value of amniotic fluid IL-6 concentration for the diagnosis of intra-amniotic inflammation. The ‘empty’ dots represent fetuses with FIRS.