Risk of spontaneous abortion in women occupationally exposed to anaesthetic gases: a meta-analysis.

Cohen et al 1971" 36 Operating room nurses

'9 Rosenberg and Kirves 197323 Cohen 1974

Nurse anaesthetists

Physicians, anaesthesia Cohen et al 19806 400 Dental assistants, high exposure Lauwerys et al 259 Operating room physicians, 1981

"5 workers, high exposure Heidam 1984'8 179 Dental assistants, private clinics, N20

Time window for Inclusion of Occurrence of pregnancies exposure Hemminki et al 1985"2 169 cases; 469 controls Nurses

Similar occupations (score=l). We included here: operating room nurses versus other nurses,"'6172425 anaesthetists versus other physicians," exposed versus unexposed anaesthetists,' exposed versus unexposed nurse anaesthetists,' exposed versus unexposed operating room nurses or technicians,' and exposed versus unexposed hospital workers.9 We see that in some of these studies, the employment status of the unexposed women was unclear or unspecified.

Dissimilar occupations (score=O). We included here: exposed workers compared with women in any other activity, including no work.'5 19-21 Any study which explicitly included unemployed women in the unexposed group received a score of 0.

Non-occupational variables may also act as confounding factors in these studies. Risk of spontaneous abortion is reported to increase with increasing maternal age,29 with smoking,'0" with alcohol consumption,'0 with use of coffee,30 and in one study, the odds ratios for the association between exposure to anaesthetic gases and spontaneous abortion were slightly lower when adjustment was made for radiation exposure.8

Control for one confounding variable (score= 1). All studies receiving a score of 1 controlled for maternal age.

No control for confounding (score=O).

Ericson and Kallen 1985'7