<qa>  What is the effect of a negative serum pregnancy test?6. Females of childbearing potential must have a negative serum pregnancy test within 48 hours prior to first infusion of catumaxomab and must use an effective contraception intrauterine devices, hormonal contraceptives, contraceptive pill, implants, transdermal patches, hormonal vaginal devices, injections with prolonged release during the study and at least 13 days after participating in the study. 