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.