You should avoid taking herbs during the first trimester. After the first trimester use very small amounts only when needed, and for short periods of time. It's really best to seek the advice of a qualified herbalist if you wish to use herbs to treat a specific problem. Talk to your obstetrician or midwife before taking any herb or medicine during pregnancy. Here is a list of the most common herbs and where they can sometimes be used for:
Alfalfa: Chocked full of vitamin K, which helps in blood clotting.
Chamomile: Helps ease nausea and is a natural anti-inflammatory.
Fish Oil: Contains omega-3 fatty acids, and boosts baby's coordination and mum's mood.
Saw Palmetto: May cause hormonal activity.
Dong Quai: Found to be a uterine stimulant and has relaxant effects, neither good in pregnancy.
Black/Blue Cohosh: Can induce premature labour.
Feverfew: A good headache remedy, but can cause allergic reactions.
St. John's Wort: Some boast it's an alternative treatment for depression, but there's little research to say it's safe for baby or that it affectively treats depression.
Red Raspberry Leaf: Is rich in iron, decreases nausea, protects against miscarriage and eases labour pains, but there is some debate about its safety during the first trimester.