Why am I spotting between my period? 5 possible reasons.

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Even if you’ve experienced it for years, the sight of blood marks in your undies generally isn’t a welcome one — especially when you know for sure they’re not a result of your period.

Spotting between periods, also known as breakthrough bleeding, is relatively common, particularly in women between the ages of 20 and 40.

However, it can signal a number of underlying causes — here are five of them.

1. You could be pregnant

When you visit your GP with concerns of spotting, the first thing they will do is rule out the possibility of pregnancy.

“It could be a normal or ectopic pregnancy and this needs to be excluded in any woman presenting with spotting, regardless of whether she is using contraception or not,” says Dr Dasha Fielder from Sydney’s Sapphire Medical Practice.

A pregnancy test from a urine sample can quickly identify or rule this out as a cause.

2. You may have an STI

Bleeding between periods could be a sign of infection and is a common sign of some STIs, including chlamydia and gonorrhoea.

Your GP can test you for a number of STIs if you think this could be the cause. (Post continues after gallery.)

Popular forms of birth control

Intrauterine deviceIUDs are small, T-shaped devices that are inserted into the uterus by a doctor in order to prevent pregnancy. There are two types of IUD: copper, which affects the movement and survival of sperm in the womb while changing the lining of the womb;and hormonal, which releases progestogen (a synthetic version of the naturally-occurring hormone progesterone) into the uterus. Although IUDs have a success rate of more than 99%, only around 2% of Australian women currently use one.

Vaginal ringVaginal rings are soft plastic rings that contain the same two hormones as the combined pill - oestrogen and progestogen. The ring is inserted into the vagina, where the hormones are absorbed into the body and then prevent the ovaries from releasing eggs. Once inside the ring can't be felt, and it needs replacing every three weeks (with one week's break in between). When used correctly, this method is more than 99% effective.

Contraceptive pillThe Pillis the most popular form of birth control. There are two types: the combined pill, containing two hormones, and theprogestogen-only, or mini, pill, which only contains one female hormone. The combined pill works by preventing the ovary from releasing an egg each month. The mini pill changes the mucus at the entrance of the uterus, which stops sperm from entering. Both are 99.7% effective; however, they don't offer protection from STDs.

DiaphragmLike the male condom, the diaphragm is a barrier method of contraception. It's a shallow silicone dome that's inserted into the vagina andcovers the cervix, which is the entrance to the uterus. It's held in place by the pelvic muscles, and works by preventing sperm from entering the uterus. After sex, diaphragms need to remain in placefor another six hours, in which time the sperm inside the vagina die. This method is 88 to 94% effective at preventing pregnancy, although this rate increases with experience.

CondomsThe male condom is a barrier contraception that prevents both pregnancy and the transmission of STDs. They work by collecting semen so it doesn't enter theman's partner's body. Condoms are 95 to 99% effective at preventing pregnancy.

The female condomThe female condom is a pre-lubricated sheath, which loosely fits inside of the vagina. The condom has a removable ring, which helps to insert the sheath and keep the condom in place. A larger ring remains on the outside to cover the opening of the vagina. They are designed to fit all women and can only to be used once. Due to misuse of the product it is only 79 per cent effective.

Birth control implantThis is a 4cm-longimplant that is inserted into a woman's upper arm, just under the skin, by a doctor. It releases a hormone called etonogestrel, which prevents ovulation and thickens the mucus in the cervix, which can stop sperm from entering. Contraceptive implants - usually sold as Implanon - are removed under anaesthetic every three years, and are close to 100% effective.

Depo ProveraDepo is a long lasting hormonal injection. The synthetic form of progesterone is administered every 12 to 14 weeks to woman, preventing pregnancy within this ongoing time period. The injection, which is given in the buttock or muscle of the upper arm, prevents ovulation and thickens the mucus in the cervix, helping to block sperm. The injections are 99 per cent effective but do not protect against STDs. Male contraceptive injections are currently being trialled

The morning after pillEmergency contraception (popularly referred to as the morning after pill) is used to prevent a pregnancy following unprotected sex. Other reasons include missing a contraceptive pill or a condom breaking. It is common in Australia to use the progestogen-only method. This entails a dosage of EC pills containing progestogen or the synthetic version. A doctor can prescribe the pill or they can be bought over the counter at a pharmacy without a prescription. Emergency contraceptionis 85 per cent effective in reducing the risk of pregnancy.

SterilisationSterilisation is a permanent form of contraception. For women there are two types of sterilisation: tubal ligation, in which clips are placed on the fallopian tubes, or tubal occlusion in which a device is inserted into the tubes. These methods work by preventing the sperm from reaching the egg. Tubal litigation is 99.5 per cent effective. The Vasectomy (for men) works by cutting and blocking the tubes called the vas deferens, preventing sperm from leaving the testicles. The chances of impregnation with a vasectomy are 1 in 1000.

3. You’ve just started on the Pill

“When a woman starts the Pill, it is not uncommon for her to get some ‘breakthrough bleeding’ but it usually settles within three months,” says Dr Mary Stewart, Medical Education Coordinator at Family Planning NSW.

This occurs as your body adjusts to the pill, but it should definitely not exceed the three-month period. If this is the case, make an appointment with your GP to discuss your options.

Spotting can also be caused by other contraceptives, whether it’s the IUD, Implanon rod or contraceptive injection. In these instances, often changing the type or dose of contraceptive device is necessary.

Spotting is common in the first 3 months of using the pill.

Women on the Pill who choose to avoid a monthly withdrawal bleed by skipping the sugar pills may find they get breakthrough bleeding after doing so for three to four months.

"It is usually resolved by having a five day break then starting active pills again," says Dr Stewart.

While women using the contraceptive implant do not usually get a regular bleed, some experience spotting. For most women it's not an issue; however if it is causing concern, Dr Stewart advises seeing your doctor for advice about how to manage it.

4. Abnormality of the cervix

"This includes a HPV infection resulting in an abnormal pap smear, or other cervical abnormalities such as a fragile cervix or polyp — an abnormal growth of tissue projecting from a mucous membrane", says Dr Fielder.

In these instances, a pap smear and gynaecological examination would be undertaken to identify or rule out this as a potential reason for spotting. (Post continues after gallery.)

History's worst contraceptives

Blacksmith water

Crocodile dung with honey

Fizzy Cola

Ground beaver testicles with moonshine.

Metal Thimbles

Onion Juice

Pig Intestines

Weasel testicles

5. Issues in the uterus

Sometimes spotting can be an indicator of issues in the uterus itself. If other potential causes have been ruled out and the bleeding continues, Dr Stewart says a gynaecological ultrasound is the next step.

5 possible reasons why you're spotting between periods.