The Effects of Antibiotics on the Fetus

Antibiotics are derived naturally from molds and bacteria or are synthesized in a laboratory and are used to treat bacterial infections. As with other drugs taken during pregnancy, antibiotics may reach the fetus by crossing the placenta and can affect the fetus in several ways. If you're pregnant and have a condition that typically is treated with antibiotics, it's important to discuss the risks and benefits with your doctor.

Antibiotics taken during pregnancy can affect the baby. (Image: Anna Omelchenko/iStock/Getty Images)

Gray Baby Syndrome

Chloramphenicol is a broad-spectrum antibiotic used to treat various bacterial infections, including eye infections and meningitis. When taken during pregnancy, chloramphenicol penetrates the placenta, and fetal drug levels reach as high as maternal levels. This increases the risk of a potentially fatal condition known as gray baby syndrome, characterized by a newborn's ashen gray body color, body limpness, cardiovascular collapse, low blood pressure, low body temperature and vomiting.

Gray baby syndrome occurs because the fetus lacks enzymes that break chloramphenicol, and it's more common in women who take chloramphenicol in the last trimester of pregnancy. A study published in the April 2000 edition of the "European Journal of Epidemiology" indicates that chloramphenicol treatment in early pregnancy presents little or no risk to the fetus.


The use of antibiotics such as chloramphenicol, sulfasalizine, trimethoprim-sulfamethoxazole and nitrofurantoin by pregnant women with a particular enzyme deficiency can lead to adverse reactions in both mother and the fetus by causing anemia and disruption of red blood cells.

The enzyme is glucose-6-phosphate dehydrogenase, or G6PD. This enzyme helps in the normal functioning of red blood cells, and the deficiency is hereditary.

Impaired Bone Development

Tetracycline is a common antibiotic prescribed to treat many infections, including pneumonia and other respiratory tract infections as well as skin infections and urinary tract infections. According to Merck Manuals Online Medical Library, tetracycline taken during pregnancy can travel through the placenta to the fetus and cause slowed bone growth, permanent yellowing of the teeth and increased susceptibility to cavities.


The aminoglycoside group of antibiotics, including kanamycin and streptomycin, act by inhibiting protein synthesis in the bacterial cell and are used to treat serious bacterial infections. Use of kanamycin and streptomycin during pregnancy puts the unborn child at risk for hearing impairment and deafness. But as points out, the benefits of these antibiotics may outweigh the risk in a potentially life-threatening situation.

Jaundice and Brain Damage

Use of trimethoprim-sulfamethoxazole and sulfasalizine in later stages of pregnancy can cause jaundice and possible brain damage in the newborn, according to the Merck Manuals Online Medical Library.

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