Hi, Taking high doses of vitamin C during conception and early pregnancy is generally considered safe and is not known to cause birth defects. However, it is recommended that pregnant women do not take excessive amounts of vitamin C supplements as it may lead to gastrointestinal upset, such as nausea, vomiting, and abdominal cramping. As for your symptoms of nausea and abdominal cramping, these are common during early pregnancy and may not necessarily be related to your vitamin C intake. Nausea and vomiting, commonly referred to as morning sickness, can occur at any time of the day and can be caused by changes in hormones during pregnancy. Abdominal cramping is also common during early pregnancy as the uterus begins to expand to accommodate the growing fetus. However, if your symptoms are severe or persistent, it is important to seek medical attention. Your healthcare provider can perform a physical exam and run tests to rule out any other possible causes of your symptoms. In summary, taking high doses of vitamin C during conception and early pregnancy is not known to cause birth defects, but excessive intake may lead to gastrointestinal upset. Nausea and abdominal cramping are common during early pregnancy and may not necessarily be related to your vitamin C intake. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician