The FDA classifies drugs into 4 major categories based on fetal risk:

1. No risk. (Currently no antibiotics are found in this category)
2. Relatively safe for fetus. Commonly used in medical practices.
3. Risks unknown. Could be potentially harmful to fetus.
4. Prominent risks, used only in extreme circumstances where there are no other alternatives

 There is also an “X” category, which includes drugs that should never be used for pregnant women, as the risks outweigh any potential benefit of the drug. Almost all antibiotics that are administered to pregnant women fall into Category B. A Category C antibiotic could be used if it is judged that the benefits outweigh any potential harm that could be done. It is only when there are severe health issues with the mother, such as possible death, and no alternatives exist that a Category D drug would be used.

 In addition to the type of antibiotic that is used, the period of the pregnancy during which the drug is administered will also alter the effect on the child. There are five prominent time periods in which antibiotics could affect the child:

1. Preconception- Antibiotics can affect gametes in either sex and develop abnormalities that will affect the development of the child
2. First week after conception- Antibiotic us during this time period will usually either have no effect or kill embryo entirely.
3. 14-60 days after implementation- This is when most antibiotic related abnormalities occur. Antibiotics can affect the development of several different organ systems. It is recommended to avoid all antibiotic treatments where possible during the first trimester.
4. Second and third trimesters- While there is a smaller risk to organ systems because they are already developed, antibiotics may affect metabolic processes which can lead to birth disorders
5. Post birth- Toxins can be transmitted through breast milk and lead to development problems early in life. This occurrence is rare but has been noted.

 Certain antibiotics can have varying levels of impact on the fetus based on when they are taken during the pregnancy. During these time periods, one must be concious of the multiple consequeneces taking antibiotics can have.

 When treating a serious infection, it is always important to weigh risks of teratogenic effects against the seriousness of the infection. If death is a likely result of the infection, then even an antibiotic that poses high risk to the fetus may be used to prevent imminent death to the mother (and subsequently the fetus). For more mild infections, a less aggressive approach should be taken. In all cases, it is necessary to evaluate all possible measures of treatment and to choose the treatment that will pose the lowest risk to the fetus. When making a decision for treatment of an infection, one must look at the magnitude of the infection, the level of risk to the fetus, and the period during the pregnancy. While it is imperative to avoid all possible teratogenic effects on the fetus, one must remember that death to the mother will cause sure death to the fetus, as opposed to the potential risk of antibiotics on the fetus.

References:

Lynch, Catherine M., John T. Sinnott, Douglas A. Holt, and Arthur A. Herold. "Use of Antibiotics During Pregnancy." American Family Physician 12 (2001): 29 Sept. 2007.

Meyer, Joette M., and Keith A. Rodyold. "Safety and Toxicity of Antimicrobials During Pregnancy." Infect Med 11 (2005): 600+. 29 Sept. 2007.

"Pregnancy Drug Dangers." MedicineNet.Com. 23 Apr. 2002. 30 Sept. 2007 <http://www.medicinenet.com/pregnancy_drug_dangers/article.htm>.