Study design and population
This is a retrospective case-control study comparing the clinical characteristics and outcomes of singleton pregnancies in women with preeclampsia with severe features who were delivered prior to 34 weeks of gestation with and without aPL antibodies. The study was conducted in a single university-affiliated tertiary referral center. Data were collected from the medical chart of pregnancies presenting with the above diagnosis between 2005 and 2014.
All women who gave birth to a singleton neonate at or before 34 weeks gestation with the discharge diagnosis of severe preeclampsia were considered for inclusion in the study. The primary exposure of interest consisted of the presence or absence of aPL antibodies. Medical records of eligible study participants were scanned to document the results of aPL antibodies work-up. Women with no evidence of aPL antibodies work-up results in their medical charts were contacted by phone after delivery and invited to complete an aPL antibodies work-up in our institution. Therefore, the presence or absence of aPL antibodies was documented after delivery and did not impact on clinical management during pregnancy or delivery.
Inclusion criteria included: 1. Delivery at or before 34 completed weeks of gestation because of preeclampsia with severe features; 2. Singleton pregnancy.
Exclusion criteria included: 1. Multifetal pregnancy; 2. Lack of available data on pregnancy and delivery; 3. Pregnancies complicated with congenital anomalies; 4. Lack of information on the presence or absence of aPL antibodies.
Presence of aPL antibodies was defined as any single positive antiphospholipid test, including lupus anticoagulant (LAC), anticardiolipin (aCL) IgG or IgM, and anti- β2-glycoprotein1 IgG or IgM. The presence of LAC was confirmed by two different clotting assay principles: activated partial thromboplastin time (APTT)-based assays and dilute Russell’s viper venom time (dRVVT). The presence of aCL and anti-β2GP1 antibodies of IgG or IgM isotype was tested by standardized enzyme-linked immunosorbent assay (ELISA). Moderate to high levels of aCL IgM/IgG and anti-β2GP1 IgG/IgM were defined as >99th percentile or >40 GPL or MPL units, according to the cutoff levels recommended in the revised Sapporo criteria.20
Within this cohort of pregnant women with preeclampsia with severe features who gave birth prior to 34 completed weeks, we therefore compared two groups: the study group – aPL-positive group - comprised of women with evidence for the presence of aPL antibodies, while the control group - aPL-negative group - included women with no evidence of aPL antibodies. Confirmatory repeat testing of aPL antibodies was recommended to all participants, but the results were not available for this study.