A dentist, pregnant in gestational week 6, treats patients with nitrous oxide (eg dinitrogen oxide)

Fråga: A dentist, pregnant in gestational week 6, treats patients with nitrous oxide (eg dinitrogen oxide). Is this occupational exposure hazardous to the fetus?

Sammanfattning: There are two recent studies which on a larger scale investigate the hazards to the fetus of nitrous oxide exposure. In one, the methodologically weaker, high exposure of nitrous oxide (unscavenged exposure) was associated with an increased risk of spontaneous abortion. In the other study, a reduced birth weight was observed. Older data, in humans and in experimental animals, indicate a small, non-specific, increase in the rate of malformations. Existing data suggest that nitrous oxide exposure during pregnancy should be avoided.

Svar: Similar questions have been raised and answered in Drugline twice previously (1,2). According to these answers, studies published 1975-1993 show that nitrous oxide is associated with reduced weight at birth in experimental animals and in man. The miscarriage rate was increased frrom 3.6 to 5.5 per cent and there was a non-specific increase in the number of congenital malformations. These studies were not controlled for factors like stress-load. In recent years the results of two major studies have been published. In one, an epidemiological Swedish study of midwives (3,4), it was found that shiftwork was associated with preterm delivery and low birth weight while nitrous oxide use was related to reduced birth weight (3). Teratogenic effects were not discussed in that paper. In the same study cohort the frequency was increased of late (> 12 weeks) but not at early spontaneous abortions in shift workers while nitrous oxide did not affect pregnancy outcome (4).

The second study was an epidemiological study of Californian dental assistants (5) based on a questionnaire to which 69 per cent replied. In this study the use of nitrous oxide, without a scavenging system, was associated with an increased risk of spontaneous abortion. Furthermore, there was a trend towards a dose-response relationship. In case the nitrous oxide was scavenged by means of an exhaust through the ventilation mask, there was no increase in the risk of spontaneous abortion. The weakness of this study is the incompleteness of the data. 1 Drugline no 10753 (year 1993) 2 Drugline no 03939 (year 1983) 3 Bodin L, Axelsson G, Ahlborg G Jr: The association of shift work and nitrous oxide exposure in pregnancy with birth weight and gestational age. Epidemiology 1999; 10: 429-436 4 Axelsson G, Ahlborg G Jr, Bodin L: Shift work, nitrous oxide exposure, and spontaneous abortion among Swedish midwives. Occup Environ Med 1996; 53: 374-378 5 Rowland AS, Baird DD, Shore DL, Weinberg CR, Savitz DA, Wilcox AJ: Nitrous oxide and spontaneous abortion in female dental assistants. Am J Epidemiol 1995; 141: 531-538