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(Date of issue: January 2017, Version: 2)

This is a UKTIS monograph for use by health care professionals. For case-specific advice please contact UKTIS on 0344 892 0909. To report an exposure please download and complete a pregnancy reporting form. Please encourage all women to complete an online reporting form.


Methylthioninium chloride (methylene blue) is a heterocyclic aromatic compound used as an indicator in analytical chemistry, a histological stain, a germicide, a diagnostic dye to identify and visualize anatomical structures, and as an antidote in the treatment of methaemoglobinaemia. Prior to 1990 methylene blue was also used in diagnostic amniocentesis in twin pregnancies.

There are extremely limited data concerning first trimester exposure or maternal systemic administration of methylene blue during pregnancy. Three pregnancies with inadvertent methylene blue exposure in the first trimester and an additional nine with exposure in the first four months of pregnancy, all of which resulted in healthy live births, have been described in uncontrolled case reports/series. A single case report of maternal systemic exposure at 34 weeks of gestation did not document any adverse maternal or fetal effects. One population-based cohort study was located which reported a non-significant increased risk of congenital malformation following exposure at any time in pregnancy. The available data are thus currently considered too limited to exclude the possibility of adverse fetal effects following maternal systemic exposure.

Intra-amniotic methylene blue exposure in the second trimester has been associated with increased risks of intestinal atresia, fetal death and stillbirth, and neonatal complications including haemolytic anaemia, hyperbilirubinemia, methaemoglobinaemia and respiratory distress have been reported following intra-amniotic exposure close to delivery.

As with all chemicals, unnecessary exposure to methylene blue should be avoided. However, where occupational exposure is unavoidable, precautions should be taken to ensure that exposure is well within the recommended exposure limits and not associated with toxic symptoms.

The management of methaemoglobinaemia during pregnancy should be the same as for a non-pregnant patient. If methylene blue is indicated in the treatment of a pregnant patient with methaemoglobinaemia, the risks to the fetus of leaving the mother untreated are likely to be substantially greater than the risk from maternal treatment. However, there are limited data to confirm this hypothesis.

Given the extremely limited published cases of first trimester and/or systemic methylene blue exposure, it is not possible to provide a fetal risk assessment following such an exposure. The mechanism by which second trimester intra-amniotic exposure induces intestinal atresia is as yet uncertain, and similar effects following other routes of exposure cannot be excluded. Enhanced fetal monitoring following methylene blue exposure at any stage of pregnancy may therefore be justifiable. Discussion with UKTIS is recommended in all cases.

This document is regularly reviewed and updated. Only use full UKTIS monographs downloaded directly from TOXBASE.org to be sure you are using the most up-to-date version. The summaries of these monographs are openly available on UKTIS.org.

This is a summary of the full UKTIS monograph for health care professionals and should not be used in isolation. The full UKTIS monograph and access to any hyperlinked related documents is available to health care professionals at www.toxbase.org.

If you have a patient with exposure to a drug or chemical and require assistance in making a patient-specific risk assessment, please telephone UKTIS on 0344 892 0909 to discuss the case with a teratology specialist.

If you would like to report a pregnancy to UKTIS please click here to download our pregnancy reporting form. Please encourage all women to complete an online reporting form.

Disclaimer: Every effort has been made to ensure that this monograph was accurate and up-to-date at the time of writing, however it cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes of the measures recommended. The final decision regarding which treatment is used for an individual patient remains the clinical responsibility of the prescriber. This material may be freely reproduced for education and not for profit purposes within the UK National Health Service, however no linking to this website or reproduction by or for commercial organisations is permitted without the express written permission of this service. This document is regularly reviewed and updated. Only use UKTIS monographs downloaded directly from TOXBASE.org or UKTIS.org to ensure you are using the most up-to-date version.