Strengths and limitations:
One of the weaknesses of this study is that the database does not permit the authors to determine the prevalence of DS diagnosis in infants born to mothers with DS. This could help us determine if children born to mothers with DS are at increased risk of other malformations, except DS. Another limitation of this study is the lack of clinical information such as congenital anomalies in the mothers and their intellectual disability which could have attributed to determining if mothers with less comorbidities and higher IQ are more likely to become mothers.
Despite the drawbacks of our study, it has several strengths. This database included 9 million women which permitted us to select a well matched control group. It is the first study to look into obstetric outcomes in mothers with DS with a sample size of 185 pregnancies in mothers with DS. The remaining published literature is mainly case-reports.
The study contained data from 2004 to 2014 inclusively and was based on ICD-9 codes. In 2015, ICD-10 codes were introduced into the database, and with which ICD-9 codes are not comparable. As such, we feared that a new code would jeopardize the existing validated codes in the literature. As such, data from 2015 onward which was available at the time of analysis was not included in this study.