Chapter 9 238 First, it is important to compare UP rates between populations from similar geographical regions. Most studies on UPs are employed in samples of young women, mostly from low- or middle-income countries and/or where limited access to safe abortion care is the norm1 and these studies may not be comparable to Dutch studies. Data from a Rotterdam obstetric cohort reported a prevalence of UPs of 25.7% in women without previous depression among women living in an urban setting, versus 36.5% unplanned pregnancies in women with a history of depression2. This concords with the prevalence of 29% in the MoMentUM dataset from Amsterdam (Chapter 4) among women without psychiatric vulnerability and other studies on UPs in Northern-Europe3. The comparable estimates of UPs amongst different groups of women with and without psychiatric vulnerability increases the credibility of our findings. Another strength of the MoMentUM study is that we adjusted for variables that were previously related to UPs, such as ethnicity, employment status, age and parity in estimating the odds of UPs between women with versus without psychiatric vulnerability. A second precaution in the measurement of UPs is the distinguishment between various samples from which to measure UPs. UPs can be measured as 1) the lifetime prevalence within all people (with and without children), 2) the lifetime prevalence within people with children, 3) the proportion within all (live) births in a group, 4) the proportion within all pregnancies within a group (including abortions and births) and 5) the proportion of all pregnancies within one person. Many studies present data from prospective and retrospective birth cohorts3. It is worth considering the possibility of missing data on the proportion of the UPs that ended in (involuntary) abortion, which would then skew the interpretation of UP rates of continued pregnancies. The complexity of estimating UP rates is demonstrated in two of our own samples, in which we found a lifetime UP prevalence of 21.7% in individuals with psychiatric vulnerability (Chapter 3) similar to data based on a sample that represents the general Dutch population (20% UPs)4. However, from retrospective cohort data, 39% of the continued pregnancies was unintended amongst women with psychiatric vulnerability. This is 10% more, a significant difference, compared to women without psychiatric vulnerability (29%) (Chapter 4,2). The large sample size of the MoMentUM study increased statistical power of these analyses and facilitated the inclusion of several relevant variables in the adjusted regression analyses. Moreover, 45.4% of the persons with children in a nationwide sample of individuals with psychiatric vulnerability (men and women) ever experienced a UP or fathered a child after a UP (Chapter 3). From these findings we might derive a trend wherein women with psychiatric vulnerability have more UPs compared to women without psychiatric vulnerability, compared to their geographical counterparts.
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