The Most Common Reasons for Irregular Menstrual Bleeding, According to a GP

The experience of having a period is a strange one. Common though it may be, no two people will experience the same journey with their period, and the way in which your menstrual cycle will change over the course of your (and its) life is an unpredictable and often frustrating experience for many. One of the most unsettling elements of this is mid-cycle bleeding – as in bleeding that occurs outside your regular period.

We’ll preface this article by stressing that if you ever experience discomfort or bleeding that feels concerning to you – or any symptoms related to your period that worry you, for that matter – it’s best to reach out to your doctor for personal advice. However, if you’ve ever wondered why mid-cycle bleeding can happen for those with a period, we chatted with Kin Fertility GP, Dr Kirsty Wallace-Hor, who shared some general insights.

Let’s take a peek.

First of all, let’s take a look at the menstrual cycle as a whole

Dr Wallace-Hor shared that there are four phases of the menstrual cycle you need to know about.

The below comes via Dr Wallace-Hor.

• Menstruation (lasts about 3-7 days): When the lining of the uterus is shed
• The follicular phase (typically lasts about 10-14 days): This technically starts on the first day of the cycle (i.e. your period) and ends with you ovulating. It reflects the time when follicles are developing on (sic) your ovaries. Usually, one follicle becomes the dominant follicle, which releases the egg for that cycle.
• Ovulation: When an egg is released from an ovary and travels to the uterus via a fallopian tube. This usually happens about two weeks before the next period.
• The luteal phase (typically lasts 12-14 days): This is when there is a big rise in the hormone progesterone and the lining of the uterus thickens to potentially support a pregnancy. If there is no pregnancy, the progesterone drops again, and the next period begins.

Why do people experience bleeding between periods?

As we touched on earlier, there’s no one answer for this, and people can certainly have very different experiences, so please speak to your doctor about concerning symptoms. However, Dr Wallace-Hor did explain that there are a few reasons you might bleed throughout your menstrual cycle.

“We obviously get bleeding during menstruation,” she shared. This, also known as your period, is “when the lining of the uterus that has built up during the cycle is shed”.

However, “If you’re using hormonal contraception or have certain conditions (such as polycystic ovarian syndrome), you might not menstruate regularly or at all,” Dr Wallace-Hor added.

Looking at bleeding between periods specifically, Dr Wallace-Hor touched on an experience known as ‘intermenstrual bleeding’.

“This can be cyclical or acyclical (that is, at a regular time in your cycle, or randomly),” she shared.

“Cyclical bleeding can happen in the middle of the cycle. This is usually only a small amount of bleeding and it’s likely related to the drop in oestrogen levels that occurs right after ovulation.”

And for those on hormonal contraception, irregular bleeding is actually something many people experience.

“It’s not uncommon to get some irregular bleeding or spotting on the pill – particularly in the first three to four months of starting a pill or when changing pills,” Dr Wallace-Hor shared.

“The risk is higher with progesterone only pills (aka mini-pills), low dose combined pills, if you skip periods with the pill, or if you have endometriosis.”

Usually, she explained, this will stop after the first few months and skipping your monthly bleed should become easier, too. However, if you’re in the early stages of taking a new pill and have experienced some spotting, Dr Wallace-Hor shared that the most common reason is “the progesterone in hormonal contraception”.

Progesterone “can cause the endometrium (the lining of the uterus) to become unstable. The oestrogen in the combined pill can help offset this instability, but it doesn’t always work (this is why the risk of breakthrough bleeding is higher in progesterone-only forms of contraception and combined pills with lower oestrogen doses),” she said.

If the irregular bleeding outside your pill ‘period’ persists, she suggests chatting with your doctor, who may recommend swapping pills or taking on another contraception option.

While Dr Wallace-Hor shared that irregular bleeding while on the pill doesn’t usually point to reduced effectiveness of the contraception form, “people on the pill can still get irregular bleeding for the same reasons as people who aren’t taking the pill”.

“Therefore, if you get persistent or new irregular bleeding on the pill, it’s important to see your GP to exclude things like pregnancy (uncommon but it happens!), infection and other abnormalities,” she said.

Bleeding between periods can in some cases “be caused by infection (e.g STIs like chlamydia), benign growths such as cervical polyps or uterine fibroids, or endometriosis. Rarely, it can be caused by cancer of the vagina, cervix or uterus. If you get new bleeding between periods, particularly if it’s persistent, it’s important to see your GP, even if you’re up to date with your cervical screening or STI screening.”

All in all, the most important thing is that you’re aware of how your menstrual cycle works and what is and isn’t normal for your body. There are loads of reasons for bleeding between periods, and while it can be unsettling, the best thing you can do is stay informed so you know you’re taking care of your health to the best of your ability.