Ectopic pregnancies that fail methotrexate therapy are predominantly euploid by comparative genomic hybridization (CGH). This feasibility study also confirms that formalin-fixed paraffin-embedded gestational tissue can successfully undergo CGH. Ectopic pregnancies that fail methotrexate therapy are predominantly euploid by comparative genomic hybridization (CGH). This feasibility study also confirms that formalin-fixed paraffin-embedded gestational tissue can successfully undergo CGH.