Blue Shield of California has this to say about Sassafras:
https://www.mylifepath.com/hw/articles/hw_article.jsp?articleId=HWHN-3661007&fromTopics=all_topics

Safrole causes liver cancer if given to laboratory animals "in high doses and for extended periods of time." This requires metabolism of safrole by the liver into other toxic compounds, though the liver also removes some of these compounds for excretion through the urine.The overall risk of sassafras causing cancer in humans is thought to be low because it is only weakly active and the amounts normally consumed are low. To eliminate the risk, sassafras products that contain safrole should not be consumed.

Safrole and its toxic metabolites do cross the placenta and enter breast milk in laboratory animals, and thus sassafras should be avoided by women who are pregnant or breast-feeding.

and from:
http://www.heartspring.net/pregnancy_nutrition.html

Few studies have been conducted testing herbal preparations in pregnancy. Some of these products, including sassafras, borage and comfrey have ingredients suspected of causing hepatic failure and have carcinogenic potential.

and finally from:
http://www.mwmc.org/topnav/library/pregnancycenter/articles/Pregnancy+Tips/TakingherbsduringpregnancySomehelpbutotherscanharm.htm

Herbs that can cause birth defects: Autumn crocus, mugwort (artemesia vulgaris), pokeroot (phytolacca decandra), pseudoginseng (panax notoginseng), sassafras (sassafras albidum), squill (urginea maritima), tansy (tanacetum vulgare).


I am not a doctor, and my information sources are taken from the internet. I personally would discontinue use of sassafras until after the birth, and after finishing breastfeeding. Better to be safe than sorry. I would also consult my doctor in this issue, though I doubt he would have more information.

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