Interpretation
Despite these limitations, this study is the first to independently assess and validate the FMF Stillbirth Risk Calculator in a cohort restricted to IUFDs and matched live births. In our dataset, theFMF Stillbirth Risk Calculator achieved a similar performance as in the reference group.7
Two characteristics in our cohort are of note: First, we included both stillborn and live born fetuses with congenital anomalies. Despite this variation to the reference cohort, the prediction model still remained accurate with and without the consideration of congenital anomalies in our population. A recent secondary analysis of a case-control study confirmed that among stillbirths, 23.4% had one or more major anomalies compared to 4.3% of live births.19 Yet, taking these data together, it seems justified to prospectively use this model for risk stratification in stillbirth as early as at preconception, thus ahead of any eventual detection of fetal congenital anomalies later in pregnancy. Also, we considered all IUFD cases from gestational week 21+0 onwards. One reason for this is the international heterogeneity in definitions of stillbirth by gestational weeks and to address those who define fetal death as early as of week 20.3
There is a robust body of evidence for the link of nulliparity, pre-existing hypertension and increased maternal BMI to antepartum stillbirth.4 The demographic findings from our cohort support these data, as all but nulliparity were significantly more prevalent in women affected by fetal death.