The first choice of birth control for nursing mothers is non-hormonal methods. This includes condom use, which has the advantages of being readily available, and having no effect on breastfeeding. Condoms can be very effective if used correctly. Condoms offer some protection against STDS (sexually transmitted diseases) and have no risks to the mother or child, but can be irritating to vaginal tissue and may require additional lubrication.
Diaphragms also have no effect on breastfeeding, and can be very effective if used correctly. Their effectiveness depends on use with a spermicide, and they must be re-fitted after the baby is born and the uterus has returned to its pre-pregnancy size.
Spermicides have no effect on breastfeeding, and can be very effective if used according to instructions. They may be irritating to the vagina and to the male partner. Spermicides are not known to pass into the milk and affect the baby in any way.
IUDs have no effect on breastfeeding, and are very effective. There is a possible risk of expulsion or uterine perforation if the device is not properly placed or is inserted before 6 weeks postpartum.
Permanent methods such as vasectomy and tubal ligation have no effect on breastfeeding and are nearly 100% effective. These methods are considered irreversible, and should only be considered if no more children are desired. If these methods are considered, counseling is recommended for couples. Vasectomy is considered minor surgery with minimal side effects. Tubal ligation may involve short-term mother-infant separation, and has risks, as all surgery does. Anesthesia may pass into breastmilk and sedate the baby. As a general rule, tubal ligation has more risks for the mother and is considered more complicated surgery than vasectomy is for the father.
The other non-hormonal method of birth control is natural family planning. This method involves learning the signs and symptoms of infertility, and may require extended periods of abstinence. It has no effect on breastfeeding, and can be very effective if used correctly. Because it may be difficult to interpret signs of fertility during breastfeeding, this method may require additional training in order to interpret the symptoms of fertility during lactation.
If the nursing mother chooses to use a hormonal method of birth control, the second choice is progestin only methods, such as Norplant (implants), mini-pills, or injectables (Depo-Provera). All of these methods can be very effective, and may even increase milk volume. Although some of the progestin hormone may enter the breastmilk, there is no evidence of adverse effects from the small amount of hormone that passes into the milk. It is recommended that the use of progestin-only hormones be delayed for at least six weeks post-partum due to the possibility of the hormones interfering with the early establishment of lactation.
The third and last choice of birth control for nursing mothers is methods which contain estrogen, such as the standard combined oral contraceptives. These methods are very effective, but often decrease milk supply, and some of the hormone may pass into the mothers milk. Although there is no evidence of a direct negative effect on the babies of mothers taking the combined pill, there is strong evidence that in many women, estrogen can lead to a decrease in milk supply and early weaning. If the other methods of birth control cant be avoided, and the combined pill is the only option, then breastfeeding can and should be continued, since it offers many health and nutritional benefits which are important for the nursing infant or toddler. If the mother chooses to use this method, the babys weight should be monitored carefully so that adequate intake is ensured. For many mothers, a slight decrease in milk output is insignificant, and in any case, the benefits of breastfeeding far outweigh the disadvantages.
My mum got pregnant with me when she had a coil in! I'm sure they've come on in the last 30 odd years tho. 
