To determine the mechanisms responsible for cell cycle arrest and apoptosis by HF/FP, the protein expression levels of p21/Waf1 (a cyclin-dependent kinase (CDK) inhibitor), and the apoptosis-related proteins cleaved caspase-3 and PARP-1 were examined using western blotting analyses. The gene discussed is CDKN1A; the disease is hydrops fetalis.