You don't need to make this decision on your own. Always consult your physician, particularly your obstetrician, before you become pregnant.
Yes, before you get pregnant. Most birth injuries occur during the first three months of pregnancy when a woman often does not know she is pregnant. If you're planning on getting pregnant, sit down with your physician and discuss the need for prenatal vitamins and minerals along with any prescription or over-the-counter drugs you plan on taking.
When discussing this, it is important to find out under what "Pregnancy Risk Category" the drug falls. The US Food and Drug Administration has assigned a risk category to all the drugs on the market. There are six categories ranging from low risk to those drugs that are not rated at all. The FDA makes these categories based on clinical and preclinical information which can be modified as needed after a drug has been marketed.
The drugs that are not rated do not have sufficient information at this time to place them in a category. The categories rated A through D range from "no evidence of adverse effects" to "potential risks but taking the drug may be acceptable" if the need is great. The next category, X, is labeled "high risk to cause abnormalities" and is not recommended no matter what the benefits. These risk categories will help you in weighing the risks and benefits of taking the drug.
The classifications are included on the professional package labeling for each drug. It can also be found on the web sites of the manufacturers and in most comprehensive pharmacological textbooks in medical libraries.
It is also important to note that "natural" substances or dietary supplements are not necessarily safe. They are not governed by the same laws as prescription and over-the-counter drugs. Despite their claims, they have usually not been tested for safety in pregnancy.
If you're going to take any drugs, ask a physician. I would then supplement this information with my own research. It's simple and worth the effort.