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 miscarriage Miscarriage A miscarriage is the loss of a fetus due to natural causes before 20 weeks of pregnancy. Miscarriages may occur because of a problem in the fetus (such as a genetic disorder or birth defect)... read more
A permanent but subtle defect that is noticed only later in life
An increased risk of childhood cancer Overview of Childhood Cancer Cancer is rare among children. In 2021 in the United States, an estimated 10,500 children aged birth to 14 years will be diagnosed with cancer and slightly over 1,100 children will die of it... read more , 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 Radionuclide Scanning In radionuclide scanning, radionuclides are used to produce images. A radionuclide is a radioactive form of an element, which means it is an unstable atom that becomes more stable by releasing... read more )
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.