NITROUS-OXIDE AND SPONTANEOUS-ABORTION IN FEMALE DENTAL ASSISTANTS

The relation between anesthetic gas exposure and spontaneous abortion remains unresolved. We examined the effect of nitrous oxide on spontan eous abortion among female dental assistants. Questionnaires were sent to 7,000 dental assistants aged 18-39 years who were registered in Ca lifornia in 1987; 4,856 (69%) responded. Analysis was based on 1,465 r espondents whose most recent pregnancy was conceived while working ful l time. Women were asked how many times a week they worked with nitrou s oxide during this pregnancy and whether the excess gas was scavenged (vented). Relative risk of spontaneous abortion (through week 20) was calculated using a person-week model. This allowed women with current pregnancies (13%) or induced abortions (10%) to be included for appro priate time periods of risk. A total of of 101 pregnancies (7%) ended as spontaneous abortions. An elevation of risk of spontaneous abortion s was seen among women who worked with nitrous oxide for 3 or more per week in offices not using scavenging equipment (relative risk = 2.6, 95% confidence interval 1.3-5.0, adjusted for age, smoking and number of amalgams prepared per week), but not among those using nitrous oxid e in offices with scavenging equipment. This relation changed little w hen analyses were restricted to confirmed pregnancies or examined for several types of potential bias. Scavenging equipment appears to be im portant in protecting the reproductive health of women working with ni trous oxide.