Both mom and fetus need vitamin C daily — it acts as a cementing agent that holds new cells together. It helps in the growing up of the fetus and builds strong bones and teeth. And it helps the iron absorption of the mom. Try to include a vitamin C-rich food with every meal to get the most iron out of the other foods you eat. From the huge function of Vitamin C, some are described as follows on the base of pregnancy:
 

1. Vitamin C helps the absorption of iron (particularly the vegetable, or non-heme form), so it is helpful for pregnancy, when the requirement of iron is obviously high. The iron in fruits and vegetables is absorbed best if you take vitamin C or eat a little meat at the same time.
2. Vitamin C is involved in the formation and maintenance of collagen, which is the basis of connective tissue found in capillary walls, skin, ligaments, cartilage, vertebral discs, joint linings, bones and teeth.  Collagen, and thus Vitamin C, is needed for wound healing and to maintain healthy blood vessels.
3. Calcium metabolism is very much affected by Vitamin C intake. Vitamin C is an effective part of the daily regimen to keep calcium soluble and prevent it from calcifying soft tissue. Proper amounts of Vitamin C increase bioavailability of average calcium levels & preventing it from going to high.
4. Vitamin C is also a highly effective antioxidant, it is important for reducing free-radical production. Even in small amounts vitamin C can protect molecules in the body, such as proteins, lipids (fats), carbohydrates, and nucleic acids (DNA and RNA) from damage by free radicals and reactive oxygen species that can be generated during normal metabolism as well as through exposure to toxins and pollutants.
5. Ascorbic acid is further important in cellular immune functions, where it may be helpful against bacterial, viral, and fungal diseases.
6. Vitamin C is needed to make collagen, the “glue” that strengthens many parts of the body, such as muscles and blood vessels. Vitamin C also plays important roles in wound healing and as a natural antihistamine. This vitamin also aids in the formation of liver bile and to detoxify alcohol and other substances.

Rumor: It is widely (and mistakenly) believed that mothers who consume large amounts of vitamin C during pregnancy are at risk of giving birth to an infant with a higher-than-normal requirement for the vitamin. The concern is that the infant could suffer “rebound scurvy,” a vitamin C deficiency caused by not having this increased need met. Since the publication in 1965 of the report upon which this mistaken notion is based, millions of women have consumed high amounts of vitamin C during pregnancy and not a single new case of rebound scurvy has been reported.®   ®. Gaby AR. The myth of rebound scurvy. Townsend Letter for Doctors 2000;June:122.

Precaution: Especially the kind found in calcium supplements -- all reduce the amount of iron your body absorbs. So, if you drink calcium-fortified orange juice, don't take your iron supplement at the same time.
 
Dietary Reference Intake (DRI) is the latest term replacing daily dietary reference values such as Adequate Intake (AI *), Tolerable Upper Intake Level (UL),  Estimated Average Requirements (EAR), Nutrient Reference Value (NRV),  and Recommended Dietary Allowance / Intake  (RDA / RDI).
The DRI of Vitamin C for pregnant / lactating is + 45 mg.
 
Should a mom take a supplement during pregnancy?

Probably not. It's easy to get the daily requirements through food. A glass of calcium-fortified orange juice at breakfast every day is all you need.
 
Advice: To avoid stomach problems and promote better tolerance, supplements should always be taken earlier, or in the middle of a larger meal.  When taken on an empty stomach or after a meal, there is a greater risk of some tablets causing irritation, or eventually erosion of the esophageal sphincter, resulting in Gastro Esophageal Reflux Disease (GERD). It is also advisable not to lie down immediately after taking any pills. When taking a very large daily amount of a single nutrient, it is better to split it up into smaller doses to not interfere with the absorption of other nutrients in food, or nutrients supplemented at lower amounts.