Data collection and outcome definitions
Relevant clinical data from all previous non-immunized and immunized
pregnancies were collected in the OPZI 2.0 database. Furthermore, we
obtained treatment details to assess the severity of HDFN of all
pregnancies with RhD antibodies and RhD-positive foetuses . From
Sanquin Diagnostic Services, laboratory data were retrieved (including
antibody titers, ADCC results and the presence of additional
antibodies).
In the current study, ‘first immunized pregnancy ’ is defined as
the first pregnancy with RhD antibodies and a RhD-positive child.
‘Subsequent pregnancy’ is defined as the second pregnancy with
RhD antibodies and a RhD-positive child.
Our main outcome was disease severity, which was categorized as follows:
- No HDFN: no antenatal or postnatal treatment
- Mild HDFN: non-intensive phototherapy (≤2 lamps), or only one day
intensive phototherapy (>2 lamps), with or without a red
blood cell transfusion during the first month after birth
- Moderate HDFN: intensive phototherapy (>2 lamps) for more
than one day or neonatal exchange transfusion (in the Netherlands
neonatal exchange transfusion has been gradually replaced by intensive
phototherapy)
- Severe HDFN: intrauterine transfusion or HDFN-related death.
In case of missing data on disease severity, patients were assigned to a
disease category based on the other, non-missing disease parameters
(laboratory results, phototherapy duration and intensity, etc.). In twin
pregnancy, disease severity was categorized according to the most
severely affected child.