A CDC scientist reviewed the medical literature on the adverse fetal effects of the use of methylene blue (MB) dye during second trimester amniocentesis.

*MB has been injected during second trimester amniocentesis in twin pregnancies to distinguish the amniotic fluid of one twin from that of the other. This ensures that the amniotic fluid from each twin's sac is sampled independently for chromosomal and laboratory analysis.

*Intestinal atresia is a birth defect in which one or more segments of the intestine is damaged or missing, thus obstructing the passage of liquids and food. Surgical correction in the newborn period is necessary for survival.

*In the early 1990s, three reports from four countries associated the use of MB in twin amniocentesis with atresia of the jejunum and ileum (portions of the intestine). The most convincing of these was from Amsterdam, where 17 (9.6%) of the 178 twin infants from 89 twin pregnancies in which second trimester amniocentesis had been performed had intestinal atresia. Fifteen of these infants were documented to be the twin whose sac was injected with MB.

*In animal studies, intestinal atresia can result from interruption of the blood supply to the intestine of the fetus. MB causes constriction (narrowing) of blood vessels in laboratory specimens. MB injected during second trimester amniocentesis may inhibit the blood supply to the intestine of the fetus, resulting in atresia.

*MB use during amniocentesis may be harmful to the fetus. We recommend that alternative methods for distinguishing the amniotic sacs in twin pregnancies be developed. If the use of dye is felt to be unavoidable, alternative dyes, such as indigo carmine or Evans blue, should be considered. However, the effects of these dyes on the fetus have not been well studied.

© 2003