Breakthrough bleeding is unwanted or unplanned spotting or bleeding, and in this article, specifically when you are on the birth control pill. Breakthrough bleeding on the pill, while annoying, is common and not dangerous.
Why does breakthrough bleeding occur?
Breakthrough bleeding can be triggered by a few different things – maybe you have just started on the pill, stopped taking your pills, skipped a pill, ran your pill packets together, or switched pill types. If none of these applies to you, then it’s possible that your bleeding is due to another cause, and you should be checked. See our information on bleeding between periods for more.
There are four specific reasons why breakthrough bleeding might occur:
- The effect of the pill on your endometrial lining
- The dose, formulation and regime that you are on
- Your habits and behaviour when taking the pill (skipping, other medication, smoking, etc.)
- Another condition that is unrelated to your birth control pills
How the pill affects your endometrium
The pill comes in a few different forms, but the most common type is what’s known as the combined pill that contains synthetic progestin (fake progesterone) and oestrogen. These synthetic hormones have a huge effect on the endometrium – the lining of your uterus, and what ends up being your period/bleeding.
The endometrium isn’t involved in the contraceptive element of the pill, but is affected nonetheless. The response of your endometrium to the pill is predictable, and leads to us being able to figure out the patterns that will occur. This is how we know that when you stop taking the pill for 7 days on your sugar pill days that you will get withdrawal bleeding – or a fake period.
Oestrogen causes the endometrium to grow, while progesterone tells it when to stop growing. That’s how the first half of your cycle is building up the endometrial lining, while the second half keeps it steady. If you don’t get pregnant, that set amount of endometrial lining – your period – comes out of your vagina, then it all starts again.
In contraceptive pills, the progestin component is the most responsible for the ovulation-blocking effect, so the oestrogen component can be increased or decreased. The latest pills aim to use the least hormone necessary to prevent ovulation, which tends to mean less oestrogen (less than 50 μg). Less oestrogen means a less stable endometrial lining, and breakthrough bleeding can occur. Progestin can also contribute to breakthrough bleeding.
Oestrogen-progestin balance seems to be more important than just the level of oestrogen when it comes to breakthrough bleeding, but the delicate balance of the endometrium still remains a bit of a mystery – there are theories, but no concrete answers.
Hormones and dosage, and how this affects breakthrough bleeding
There are dozens of contraceptive pills available globally, with each containing its own patented blend of oestrogen and progestins. Each brand is slightly molecularly different to the others, because this is required for patents – this is why if one pill doesn’t go down very well in your body, it pays to try a few to see which works for you.
The pills that contain the lowest doses of oestrogen (≤20 μg) are associated with the most breakthrough bleeding, but low doses of either oestrogen or progestin can increase breakthrough bleeding. The type of progestin used also seems to impact breakthrough bleeding.
Breakthrough bleeding also tends to decrease the longer a woman has been taking the pills.
Biphasic, triphasic, extended-cycle or continuous use pills and breakthrough bleeding
Women on extended cycle birth control pills may see more breakthrough bleeding than those on a 28-day cycle pill. Biphasic means running two pill packets together, while triphasic means running three pill packets together, leaving just 7 planned bleeding days. In a 28-day cycle, there are 21 days of planned bleeding in the three-monthly cycle. In continous use pills, all bleeding is considered breakthrough bleeding.
Factors that contribute to breakthrough bleeding
Skipping pills is incredibly common, and a major cause of breakthrough bleeding. When electronically monitored, it was found that over 80 per cent of women on the pill missed at least one pill, with at least half skipping three or more per cycle. Taking the pill at the same time every day can also help.
Women who experience nausea were more likely to skip pills and stop taking them altogether. Additionally, women taking over-the-counter supplements or medications saw some interference in the activity of the pill, for example supplements that improve liver function can cause hormone clearance quickly, leading to breakthrough bleeding. St John’s wort is a common contributor to breakthrough bleeding and possibly ovulation.
Smoking has been associated with anti-oestrogenic effects, however the exact mechanism of this is not known. Smoking may lower oestrogen levels and cause breakthrough bleeding even in good pill-takers. Women who smoke a lot are more at risk of breakthrough bleeding than those who smoke occasionally or less.
Non-pill-related causes of breakthrough bleeding
- Endometrial polyps
- Myomas (fibroids)
- Cervical cancer
- Endometrial cancer
- Infection (chlamydia, gonorrhoea, trichomonas)
What to do if breakthrough bleeding is a problem on the pill
You can try a different pill, go off the pill and try another contraception, or adjust your dosing regime.