Timing and the Effects of Medications During Pregnancy
Time Frame | Possible Fetal 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 An obvious birth defect A permanent but subtle defect that is noticed only later in life An increased risk of childhood cancer, as may result from giving the mother radioactive iodine (to treat thyroid cancer) or using a radioactive substance in an imaging test (such as radionuclide scanning) | The fetus's organs are developing, making the fetus particularly vulnerable to birth defects. |
Second and third 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 medications are likely to have harmful effects. | ||