Treatments for breast cancer can bring about early or 'premature' menopause (stopping menstrual cycles before your body would naturally go there) and so can cause temporary or permanent infertility, meaning you're unable to fall pregnant. If you want to have children, discuss with your oncologist how breast cancer treatments could affect your fertility.  An early referral to a fertility clinic before treatment starts will also help you understand your options.    

In this section:

How do treatments affect fertility?
Preserving your fertility before treatment starts 
Fertility after treatment is finished 
Contraception during treatment 
Talking to your specialist about fertility preservation 

How do treatments affect fertility?
Everyone responds to treatment differently so it can be hard to determine exactly how medical interventions will affect your fertility. However, the risk of permanent infertility from treatments is greatest for women aged over 35 years. Periods may return, but menopause may come earlier than it would have if left to occur naturally. 
Chemotherapy affects the functions of your ovaries which means that fewer or no eggs are produced. Periods can become irregular or stop altogether during chemotherapy. Whether your periods and your fertility will recover depends on the type of chemotherapy used, the dosage and your age at commencement of treatment.  
For some women, fertility is of paramount concern. Some chemotherapies may be less harmful to the ovaries and certain hormonal treatments may be given to try and protect your ovaries during treatment. There is also the option of preserving your fertility prior to treatment.  Talking this through with your specialist team is essential.

Preserving your fertility before treatment starts
If optimising fertility preservation is important for you, here are some options to discuss with your specialist:
1. Freezing embryos:
This process using IVF (in-vitro fertilisation) is the best method if you have a partner. It is funded by the government.  Hormonal drugs are used to stimulate egg production.  The eggs are harvested and placed with sperm and any resulting fertilised eggs (embryos) can be frozen.

2. Freezing eggs:  Egg production is stimulated by hormonal drugs. The eggs are harvested and frozen and may be thawed and fertilised with sperm in the future. However, eggs can be damaged during these processes and IVF requires careful consideration for women diagnosed with breast cancer as it causes high levels of systemic oestrogen and significantly delays commencement of cancer treatment. 
Both embryos and eggs can be stored for up to 10 years.  

3. Freezing ovarian tissue:  This technique involves a laparoscopic procedure where ovarian tissue is removed and frozen. The tissue can be put back into the body later. This procedure is not recommended for carriers of the BRCA genetic mutation due to future ovarian cancer risk.  The success rate with this is low so far.
-GnRH agonists
Data regarding the effectiveness of this option is unclear but interest is building in its use as a treatment option. Gonadotropin-releasing hormone agonists are used to suppress ovarian function during chemotherapy and so protect the ovaries.  
Recent research shows this can be effective in preserving fertility for some premenopausal women during chemotherapy for hormone receptor-negative breast cancer.

Fertility after treatment is finished
Periods can come back 12-18 months after chemotherapy.  Even if your periods haven't started again it is still possible you are producing eggs and could become pregnant. However, your ovaries may have been damaged by the treatment and even though you are having periods, your fertility may have been impacted. 
Your specialist can check on your post-treatment fertility through blood tests and/or ultrasound. However the results are not always reliable if you are taking adjuvant hormonal treatments for breast cancer.
If your ovaries have been affected and you cannot produce eggs, egg donation may be an option. Once again, this requires careful discussion with your specialist.
In general, women are advised to wait at least two years post-treatment before considering pregnancy (this is due to the potential for cancer recurrence). There is no evidence indicating that treatments can harm children conceived after treatment is finished.

Contraception during treatment
Your specialist will advise you not to get pregnant while receiving chemotherapy, radiotherapy or hormone-blocking therapy. These treatments can damage the ovaries and your eggs and could harm a baby conceived during this time. He or she may also advise discontinuing oral contraceptives following your diagnosis as the hormones in the pill could stimulate growth of breast cancer cells. The use of condoms, diaphragm or IUD are all options to discuss with your specialist.

Talking to your specialist about fertility options
If you're concerned about your fertility, here are some tips that might help those discussions: 
Your prognosis:  Is your prognosis excellent, good, poor? Could you have children in the future? Is it safe for you to become pregnant?
Fertility preservation: Which option is best for me? Which carries the least/most risk for me? Are the hormones in IVF treatment safe for me?
Ovary suppression during chemotherapy: Is this something I should consider? 
What are my options time-wise and cost-wise?: How much time/delay is associated with each option and what are the costs
Postponing treatment to allow time for preservation: Would this be safe for me?
What are my options if my ovaries are damaged and I'm unable to produce eggs?:  Egg donor? Adoption? Surrogacy? Embryo (fertilised egg) donation?