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Late Period Or Early Miscarriage? – How To Know

Your period is late. You’re daring to hope that finally, this is the month you’re going to get that BFP (big fat positive)! But you don’t want to take a pregnancy test just yet. You don’t want to tempt fate, so you’re just going to wait a few more days…

And then your period arrives (darn it!).  And along with the heavy feeling of disappointment, so come the questions. Why was your period so late? Could it have been a very early miscarriage? How can you find out?

In this article, I’m going to discuss the difference between a ‘late’ period and a very early miscarriage, and how it’s possible to find out the difference.

What exactly is a very early miscarriage?

A very early pregnancy loss occurs when an egg has been fertilised but, for one reason or another, it doesn’t go on to become an established pregnancy.

This is an extremely common event. In fact, it’s thought that a whopping 60% of human conceptions are lost before a woman even misses her period! 

Half of these very early pregnancy losses occur before the fertilised egg has implanted in the uterus lining and half are thought to occur after implantation (implantation is when the fertilised egg burrows into the uterus lining, about 7 – 10 days after ovulation).

If a pregnancy is lost before implantation, your period will come as normal, and you’ll never know that conception had occurred.

But if a pregnancy is lost after implantation, this can cause a delayed period.

Once the fertilised egg has implanted in the uterus lining, it starts producing hCG – the hormone that pregnancy tests measure. This hormone triggers your body to hold on to your uterus lining, rather than to lose it as a period.

So during the time that hCG is being produced after implantation, it sends your body a message to NOT have a period. The longer the implanted embryo grows and produces hCG, the longer you’ll go without a period.

In the case of a very early miscarriage, once the embryo stops developing the hCG levels drop, and this will be followed by a bleed. This bleed can come just a few days after your period was due.

What exactly is a ‘late’ period?

A late period means that your period comes later than expected, but without you having conceived. In most cases, you’ll find your period comes just a few days later than normal. But sometimes it might be late by up to a week or more.

A late period is almost always due to a late or delayed ovulation (more on this below).

There are a number of factors that can cause a delayed ovulation and a delayed period. These include:

  • Stress
  • Illness
  • Travel (especially across timezones)
  • Hormonal imbalances caused by conditions such as thyroid dysfunction and PCOS (polycystic ovary syndrome)
  • Being overweight or underweight
  • Sudden weight gain or loss
  • Coming off birth control
  • Certain medical conditions
  • Early peri-menopause

Early miscarriage or late period – how to tell?

So how can you tell if your delayed period was simply due to a late ovulation or if it was actually due to an early miscarriage?

Unfortunately in retrospect, it’s not always possible to tell. BUT, with a little knowledge in advance, you CAN find out.

The KEY to knowing whether or not you’ve had an early miscarriage, is to understand and monitor the different phases of your menstrual cycle.

What you need to know to figure it out

There are 2 things you need to know, to figure out whether your delayed period was due to an early miscarriage or not: the day that you ovulated on and the length of your luteal phase.

1. The day that you ovulated 

The day that you ovulate can CHANGE from month to month. This timeframe makes up the first part of your menstrual cycle – the follicular phase (see the diagram above).

If it takes you 11 days to ovulate, then your follicular phase will be 11 days long. If it takes you 25 days to ovulate, then your follicular phase will be 25 days long.

The important thing to remember is that your follicular phase can CHANGE from cycle to cycle. This is usually due to natural variation or external factors like illness, travel or stress.

2. The length of your luteal phase

Unlike the follicular phase, the length of the luteal phase does NOT change from cycle to cycle. A normal luteal phase length is between 10 and 16 days long. Different women will have a different luteal phase length.

A luteal phase is usually NO LONGER than 16 days in length.

Putting it together

So, for any given month, the length of your menstrual cycle and the day that your next period is due, depends on:

Your follicular phase length (the day that you ovulate) PLUS your luteal phase length

short follicular phase (early ovulation) will mean a short cycle.

long follicular phase (delayed ovulation) will mean a long cycle.

So, using the examples above:

If your luteal phase length is normally 15 days long, and you ovulated on Day 10 (your follicular phase was 10 days long), then your cycle would be 25 days long.  Your period would therefore be due on Day 26.

If your luteal phase length is normally 15 days long, and you ovulated on Day 20 (your follicular phase was 20 days long), then your cycle would be 35 days long.  Your period would therefore be due on Day 36.

By using this simple formula, you can figure out exactly when your period is due, and therefore when it is genuinely overdue.

You’re likely to have had an early miscarriage if:

1) Your period comes 3 or more days after it’s actually due (using the equation above and allowing for some error) and/or

2) Your luteal phase extends beyond 18 days in length

It can help to do a pregnancy test as soon as your period is overdue.  If hCG is still being produced at that stage (and it’s at least 14 days after ovulation), you are likely to get a positive result. 

If you get a positive test followed by your period, you’ll know that sadly, you did experience an early miscarriage. A positive pregnancy test followed by a period is known as a biochemical pregnancy.

It’s also possible to get a negative pregnancy test, and still have had a very early miscarriage.

Knowing that you’ve had an early miscarriage can be absolutely devastating – especially knowing that a pregnancy was ‘so close’.  The silver lining is that an early miscarriage can help to answer a number of critical questions about your fertility.

And it’s important to remember that most women who experience a miscarriage, will go onto have a healthy pregnancy in future.

So how can you work out your day of ovulation and luteal phase length?

1) Learn fertility awareness and chart your fertility

In my opinion, this is by far the most reliable method. Not only is it the most accurate in determining your day of ovulation and luteal phase length, but it also provides you with a wealth of additional information about your menstrual and reproductive health.

2) OPKs (ovulation predictor kits)

OPKs can be used together with fertility charting or on their own. Unfortunately they’re not as accurate in determining your day of ovulation or luteal phase length, so this can be problematic if you’re trying to figure out if you’ve miscarried. 

Repeat early miscarriage

A single early miscarriage doesn’t mean that you’re less likely to get pregnant the next time around.  In fact, most women who miscarry go on to have healthy pregnancies in the future.

But if you know or suspect that you’ve experienced 2 or more early miscarriages, it’s important to let your doctor or fertility specialist know, so that they can investigate possible causes. 

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Olivia Williams

Olivia Williams

All things about menstruation

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