Strengths and Limitations
To our knowledge, this is the first study assessing the combined
contribution of maternal and paternal preconception overweight and
obesity on infant birthweight. The strengths of our study include the
use of a database in which preconception health, IVF cycle outcomes and
pregnancy rates were registered prospectively, thereby minimising
selection bias; BMI was calculated from clinically recorded measurements
of maternal and paternal preconception weights and heights; the analysis
only included first singleton term births; and the large population size
from a singular ART unit limited variability in clinical protocols.
Limitations of our study include the retrospective study design, which
limits the degree of causal inference; reduced ability to control for
some key parental factors that can influence infant birthweight,
including parental smoking 15, 16 and maternal
gestational weight gain 17 and further, the fact that
the utilization of an ART cohort is confounded by subfertility andin vitro embryo culture. However, infertility diagnosis has been
previously shown to not influence infant birthweight in term pregnancies18, 19, thus the subfertility diagnosis is unlikely to
be contributing to the reported outcomes.