The effect of pregnancy on the sympathetic activity in the maternal cardiovascular system.

Pregnancy induces cardiovascular adjustments pivotal for normal pregnancy
development. These changes are induced by vasorelaxing stimuli from the
trophoblast, which leads to baroreceptor activation and with it, the
institution of a high flow and low resistance circulation. To preserve the
latter for the duration of pregnancy, plasma volume is to expand and
cardiovascular compliance to increase. The impact of the initial fall in
peripheral vascular resistance on cardiovascular sympathetic activity has never
been studied longitudinally in normal pregnancy. This information will not only
unravel the role of the sympathetic nervous system in the maternal
cardiovascular response to pregnancy. It may also prove to be clinically
valuable as a reference for the early identification of complicated
pregnancies. Currently available easily applicable, non-invasive techniques
will be used in this study to explore the pattern of cardiovascular sympathetic
activity in healthy human pregnancy.

This study aims to explore the pattern of change in cardiovascular sympathetic
activity in response to pregnancy by estimating the central sympathetic
activity by measuring the pre-ejection period (PEP). The PEP is considered the
golden standard for the non-invasive measurement of cardiac sympathetic
activity. Secondary, skin conductance (SCL), which provides an estimate for
peripheral sympathetic activity, will be measured concomitantly to determine
whether this is complementary to the PEP. The SCL has been validated as an
estimate for peripheral sympathetic activity, is easy applicable in combination
with PEP and does not put extra strain upon the subject. We will measure
PEP/SCL on 3 consecutive occasions in the first trimester of pregnancy, when
functional changes in the maternal circulation are largest, at 20 and 28 weeks,
when the cardiovascular adaptation has reached a plateau, and at six weeks
post partum, when the cardiovascular sympathetic activity is expected to have
returned to baseline.

Prospective longitudinal observational study in healthy normotensive pregnant
women with a normal pregnancy course and outcome.

The risk of study participation is negligible. The burden of the study is
minimal as the measurements are non-invasive and do not involve potentially
harmful manipulations. The orthostatic stress test has been used many times in
earlier research and carries a low risk for healthy participants. If - in rare
conditions - the participant experiences dizziness during the test, the test
will be discontinued and the participant will be allowed to recover by lying on
a bed. During the test, a researcher will always be present. The participant
herself does not benefit from the study results but contributes to increasing
our insight in pregnancy physiology.