Prenatal VITAMIN D is more important than other prenatal vitamins

CDC review of Folic acid - not much benefit
Prenatal vitamins: A review of the literature on benefits and risks of various nutrient supplements
Iron-deficiency anemia in pregnancy - Baby Center, Oct 2014
Do all pregnant women need to take iron supplements? - PubMed, March 2014
Preconception (not prenatal) multivitamins help
Neural tube defects (in mice) reduced by Vitamin D
See also VitaminDWiki
- Pregnancy category starts with

CDC review of Folic acid - not much benefit

Updated Estimates of Neural Tube Defects Prevented by Mandatory Folic Acid Fortification — United States, 1995–2011 Jan 2015

Folic acid fortification (before pregnancy) may have reduced defect rate in whites by 3 per 10,000
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Vitamin D (during pregnancy) has been proven to reduce premature birth rate by 500 per 10,000
As well as provide other benefits (from Grassroots Health)

Prenatal vitamins: A review of the literature on benefits and risks of various nutrient supplements

Formulary journal, January 31, 2013 By Anna K. Sfakianaki, MD
Download the PDF from VitaminDWiki

Folic Acid

Folic acid supplementation helps if done before pregnancy, but not so much 8 weeks after conception
"Folic acid supplementation may also be beneficial for preventing other congenital anomalies such as cleft lip/palate and heart defects; however, evidence from randomized trials is lacking."

Omega-3 fatty acids

4 RCTs found no consistent benefit
1 RCT found a slight reduction in preterm birth and low birth weight
"A systematic review found no consistent effect of supplementation during pregnancy or lactation on infant and child body composition."

Iron

"Although the treatment of iron deficiency anemia is not debated, the benefits of iron supplementation in healthy women have been questioned, and some studies of iron supplementation have demonstrated harm"
"A Cochrane review of 49 trials involving more than 20,000 pregnant women. . . no differences in maternal or neonatal clinical outcomes"
"In addition, significant adverse effects were noted, especially hemoconcentration and constipation."

Vitamin C (1,000 mg) and vitamin E (400 IU) for the prevention of preeclampsia

not only were the vitamins not protective but also that women who received the supplements actually had increased risks of gestational hypertension and premature rupture of membranes"

MULTIVITAMIN USE in developing world

"Two recent systematic reviews and meta-analyses have demonstrated a decreased risk of SGA and LBW infants in women who received multimicronutrient supplements versus those who received standard iron-folic acid supplementation"
'Reductions in miscarriage, preterm birth, and stillbirth have not been consistently noted"
"The literature regarding preterm birth is conflicting, with some studies showing a decreased risk, some showing no effect, and 1 study showing an increased risk of preterm birth with multivitamin use."

Iron-deficiency anemia in pregnancy - Baby Center, Oct 2014

http://www.babycenter.com/0_iron-deficiency-anemia-in-pregnancy_3073.bc

Your iron requirements go up significantly when you're pregnant.
During pregnancy, the amount of blood in your body increases until you have almost 50 percent more than usual.
See also VitaminDWiki
Iron deficiency is a cause of Vitamin D deficiency
Iron Supplement Heme iron polypeptide (HIP) appears to be 23X better than others
Anemia in pregnant teens 7X more likely if low vitamin D – April 2015

Do all pregnant women need to take iron supplements? - PubMed, March 2014

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072758/

Iron supplements are particularly important for pregnant women who have anemia.
In women who have normal blood values, taking iron supplements as a precautionary measure probably does not have any health benefits.
Taking high-dose iron supplements prevented low birth weight in 1 out of 100 children.
. . .higher-dose iron supplements may cause side effects. These include, in particular, gastrointestinal (stomach and bowel) problems like constipation, nausea, vomiting and diarrhea

VitaminDWiki summary: High dose Iron prevents low birth weight in 1% of children but causes side effects in 20% of pregnant women

Preconception (not prenatal) multivitamins help

Association of periconceptional multivitamin use and risk of preterm or small-for-gestational-age births
Am J Epidemiol. 2007 Aug 1;166(3):296-303. Epub 2007 May 11.
Catov JM1, Bodnar LM, Ness RB, Markovic N, Roberts JM.

The authors' objective was to determine the relation between periconceptional multivitamin use and the risk of small-for-gestational-age (SGA: <5th percentile; 5th-<10th percentiles) or preterm (<34 weeks; 34-<37 weeks) births. Women in the Pregnancy Exposures and Preeclampsia Prevention Study (1997-2001) reported at enrollment their regular multivitamin use in the past 6 months (n=1,823). Women were classified as users or nonusers in multinomial logistic models. After adjustment for race, age, education, enrollment gestational age, and household density, periconceptional multivitamin use was associated with a reduced risk of preterm births (<34 weeks) (odds ratio (OR)=0.29, 95% confidence interval (CI): 0.13, 0.64) and spontaneous preterm births (<34 weeks) (OR=0.40, 95% CI: 0.16, 0.99).

Risk of SGA (<5th percentile) was marginally lower (OR=0.64, 95% CI: 0.40, 1.03) after adjustment for smoking, education, parity, enrollment gestational age, and body mass index. Prepregnancy body mass index modified this relation.
Nonobese users had a reduction (OR=0.54, 95% CI: 0.32, 0.91) in risk of SGA (<5th percentile); there was no effect among obese women.

There was no effect of multivitamin use on risk of preterm births (34-<37 weeks) or SGA (5th-<10th percentiles). Sensitivity analysis for unmeasured confounding by folate intake supported these findings. Study results indicate lower rates of severe preterm births and extreme SGA in women who report periconceptional vitamin use, although these should be considered cautiously until replicated.

PMID: 17496313
PDF is attached at bottom of this page

Neural tube defects (in mice) reduced by Vitamin D

Neural tube defects of pregnant mice reduced by Vitamin D (perhaps less Folate needed) – April 2015