Background incidence rates of adverse pregnancy outcomes in the
Netherlands; data of 2006-2018.
Objective To assess background rates of adverse pregnancy outcomes
before implementation of a maternal pertussis immunisation programme in
the Netherlands, to put into perspective the safety concerns about such
outcomes following immunisation. Design Retrospective cross-sectional
study. Setting and population Dutch pregnant women and their infants who
were registered in the Dutch Perinatal Registry in the 2006-2018 period.
Births of ≥500g birth weight and ≥24+0w gestational age were included.
Methods Annual numbers of adverse outcomes were used to calculate
incidence rates per 10,000. Trends with moving-average-lines over the
past 3 years were plotted, with 95% confidence interval. Main Outcome
Measures Adverse outcomes at maternal and neonatal level. Results From
2006 through 2018, yearly numbers of pregnancies ranged between
158,868-175,710. Numbers of newborns ranged between 161,307-178,874, of
whom 160,838-178,177 were live-born. Most outcomes were stable over
time. Between 2006-2011, occurrence of labour induction increased by
68%, and postpartum hemorrhage increased by 25%. Both stabilised from
2011 onwards. Perinatal mortality up to day 7 or 28 postpartum decreased
by 38% and 37%, respectively. Occurrence of low Apgar score among
preterm infants born before 37+0w gestational age and among term infants
increased by 19% and 27%, respectively. Conclusions Our study on
background incidences showed notable increases over time in occurrence
of labour induction, postpartum hemorrhage and low Apgar score, while
showing a considerable decrease in overall perinatal mortality. These
findings should be considered when interpreting data on adverse events
occurring since Tdap vaccination was implemented.