Strengths and limitations
There are strengths in our study. Due to the detailed clinical data,
such as pre-pregnancy weight, weight measurements at every prenatal
visit and weight measurements before delivery beyond the registry, it
was possible for us to study both weight gain in different periods of
pregnancy and to take the differences in types of VTE (eg, DVT as well
as PE) into account. Moreover, use of weight gain z-scores instead of
weight gain in kilograms helped to disentangle the effects of pregnancy
weight gain on VTE from the effects of gestational duration, because GWG
is highly correlated to the gestational duration. Our cohort study
extends previous studies by accounting for effect modification by
pre-pregnancy BMI and using a gestational age-independent measure of
pregnancy weight gain.
There are also limitations in our study. The number of VTE was decreased
when stratified by BMI-categories, especially among obese women. For
this reason, we analyze the effect of weight gain during pregnancy on
VTE in obese together with overweight women. Furthermore, the incidence
of VTE might be underestimated in this study, since women who have high
risks of VTE during pregnancy typically receive low-molecular-weight
heparin (LMWH) and are often not switched to VTE in the postpartum
period, which is inevitable.