Objectives: The aim of this study is to demonstrate the most common chromosomal abnormality causing spontaneous miscarriages in first trimester pregnancies over a period of 2 years. Methods: The karyotype results of all retained products of conception sent for analysis at our Cytogenetics lab were retrospectively reviewed . Conclusions: Trisomy 16 was found to be the most common chromosomal abnormality causing spontaneousfirst trimester miscarriages .The data from this study also supports the theory that fetal chromosomal abnormalities occur particularly in pregnancies that occur in women who are 35 years of age or older.