I found this on the web when I had some spotting a couple of weeks ago. The spotting stopped so i ddin't take anything. It's all from Susan Weed:

Herbs for Miscarriage
Please be warned that no herb will stop a miscarriage that is happening because of a problem with the baby. The following remedies may be helpful if a hormonal problem is present in the mother. These herbs are also supposed to help complete the miscarriage that is not due to a hormonal imbalance. Please be careful and check with your healthcare provider first. Most of the information on this page comes from The Wise Woman Herbal for the Childbearing Year, by Susun Weed.
Black Haw Root Bark is regarded as an effective miscarriage preventative. Begin drinking one or two cups of tea or a half cup of infusion daily as soon as you are pregnant. Black Haw may be used throughout the pregnancy if desired.
False Unicorn Root is recommended for women who have experienced repeated miscarriages. It may help even if the cervix is too loose to hold the pregnancy as it is a powerful tonic. Use 3 drops of the tincture four or five times daily beginning a month before conception and continuing thoughout the first trimester.
Bed rest, relaxation, and vitamin E (up to 2000 IU during the crisis period) are strongly recommended during a threatened miscarriage. Alcohol relaxes the smooth muscles and can be used to slow or stop uterine contractions if sipped when cramping is felt.
Wild Yam Root contains hormonal precursors to progesterone and cortisone which are needed to maintain pregnancy. Take 2-4 ounces of infusion every half hour for threatened miscarriage. Results should be evident by the second dose.
Lobelia is said to aid the miscarriage if the fetus is weak or malformed but prevent it if the baby is strong and healthy. Use no more than 15 drops of the tincture in a small glass of water as often as every fifteen minutes for several days if needed. PLEASE talk to your midwife or healthcare provider before using this herb.
Threatened Miscarriage Brew: (I've used this myself to stop bleeding in pregnancy:
1 Tablespoon dried Black Haw or Cramp Bark
3 Tablespoons dried Raspberry Leaf
10 drops Wild Yam root tincture
10 drops False Unicorn root tincture
60 drops Lobelia herb tincture
Put the dried herbs in a quart jar and fill to the top with boiling water. Steep until cool enough to drink. Add the Wild Yam and False Unicorn to one cupful of the tea and drink. If contractions continue for more than thirty minutes, add the Lobelia tincture to a second cup of tea. Drink a cup every three hours, adding tinctures as needed, until miscarriage no longer threatens. Miscarriage Preventative Formula:
one ounce of the following herbs:
Wild Yam
Squaw Vine
False Unicorn root
one-half ounce Cramp Bark
Simmer for 20 minutes in one quart of water. Take one wine glassful every four hours until symptoms of miscarriage cease.

 

i love susun weed's work, and used a tea much like the one described in the previous post for two of my pregnancies which presented first trimester bleeding. it was a tonic tea with the above ingredients, plus raspberry leaf, peppermint, and spearmint, and it tasted sooooo nice. i drank separate infusions of nettle leaf as well.

the tincture described above makes me nervous because of the lobelia content. that is powerfull stuff, i would only use it under the advice and observation of a skilled midwife/herbalist.