Possible Drug* Effects
Status of the Fetus
Within 20 days after fertilization
An all-or-nothing effect (death of the fetus or no effect at all)
The fetus is highly resistant to birth defects.
3‒8 weeks after fertilization
Possibly no effect
A permanent but subtle defect that is noticed only later in life
The fetus's organs are developing, making the fetus particularly vulnerable to birth defects.
2nd and 3rd trimesters
Changes in the growth and function of normally formed organs and tissue
Unlikely to cause obvious birth defects
Unknown long-term effects
Organ development is complete.
* Only certain drugs are likely to have harmful effects.