The absence of more detailed information on psychosocial
factors and socioeconomic status limits our ability to eliminate
these potential confounders, but prior studies have suggested
most are not important in determining PIH risk. One potentially
important factor unaccounted for is frequency of physical
activity or exercise, which has been found to decrease the
risk of gestational hypertension and may be associated with
lower prepregnancy BMI.31 In addition, although we have
information about maternal race, we are unable to examine
subgroups within the Asian and Hispanic populations. Finally,
our data are from a single institution and may not reflect
the experience of other centers.
The well-known increase in the prevalence of overweight
and obesity in the general U.S. population has included women
of childbearing age and is reflected in the high rates of
overweight and obesity in our obstetrical population. Obesity
has been shown to increase healthcare use through several
factors, including the development of pregnancy complications.32
This is also consistent with findings that risk of adverse
pregnancy outcomes, including PIH, increase with
weight gain between pregnancies even within normal weight
ranges.33 Our study quantifies the magnitude of the effect of
obesity on the risk of PIH independent of related maternal
comorbidities and demonstrates that the risk of PIH rises with
BMI from underweight through obesity.