I have been taking Duet DHA ec prenatal vitamins for about 6 months. The company confirmed that they are gluten free. Each dose is a prenatal vitamin tablet and an enteric-coated softgel capsule. The capsule contains DHA and EPS (omega-3 fatty acids). I have found that they do not cause nausea. I do, however, take them right before I go to bed. Here is a link that shows a comparison of the nutrients in a dozen or so prenatal vitamins: http://www.duetdha.com/files/comparison_chart.pdf
Whatever vitamin you choose, make sure it has plenty of folic acid. Since many of the folate-enriched foods (cereals, breads, etc) are off limits, you may not be getting much folate from your diet.