Milk thistle. The fewer meds you take during pregnancy (other than required prescription meds and prenatal vitamins) the better. Same goes for supplements; medical literature advises against milk thistle in hormone sensitive conditions; since maintaining a pregnancy depends on hormones, i'd advise not to use it. Beyond that there are insufficient data to aid a decision.
NO Milk Thistle=preg. No, because milk thistle plant extract might have estrogenic effects. Herbs have to used with extreme caution in pregnant and lactating mothers. Historically, milk thistle was used as a tonic for the stomach, and liver; for the gallbladder; to promote bile flow; and as a stimulant for milk flow in nursing mothers.