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Illustration by Marta Pucci and Katrin Friedmann

Cycle A-Z

Miscarriage or period: Is it a late and heavy period, or something else?

by Maegan Boutot, Science Writer for Clue
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Having your period start later than expected can be stressful. Although menstrual cycle length can vary, some people may worry that their late period is actually a very early miscarriage (also known as a spontaneous abortion).

Miscarriage, or the loss of a pregnancy in the first 20 weeks (1), is very common. At least 1 in 3 pregnancies end in a miscarriage (2), though people do not always know that they were pregnant when it happens. Sometimes the egg implants only for a short period of time, and then is lost. Most people would not know they were pregnant in this scenario. It's estimated that about 1 in 5 clinically recognized pregnancies - meaning pregnancies that most people would be aware of, often causing a missed period - end in miscarriage (2,3).

Miscarriages are most common in the first six weeks of pregnancy, becoming less likely as the pregnancy develops (2,3). If a pregnancy loss happens, it’s most likely in the first trimester (the first 13 weeks by gestational age) (4).

When a miscarriage occurs before a person knows that they are pregnant, it may be difficult to tell the difference between a normal menstrual period and miscarriage.

Symptoms of both menstrual periods and miscarriage can include:

If you are experiencing a miscarriage, someone may also notice:

  • Reduction in or disappearance of pregnancy symptoms (e.g. nausea, vomiting) (5)

  • Signs of being sick, like a fever (if the miscarriage is caused by an infection) (5,6)

If you get your period less than 2 weeks after your period is expected, it is difficult to know whether it is a late period or a miscarriage. Miscarriages in this time frame are not usually experienced with heavier or longer bleeding (7).

Also, people who miscarry this early (i.e. less than or equal to two weeks after an expected period) are highly unlikely to experience complications.

A hand holding a phone with the Clue app opened

Download Clue to track your period and bleeding.

The later into a pregnancy a miscarriage occurs, the more it will differ from a menstrual period.

Bleeding from later miscarriage will contain fetal tissue, and blood clots will likely be larger than during normal menstrual periods. The tissue will likely look different from menstrual blood in color (ex. gray), consistency/texture, and shape.

Miscarriages and fertility

Although miscarriages that happen around the time of a period don’t represent a threat to a person’s health, people may be concerned about their chance to have healthy pregnancies in the future.

Because very early miscarriages happen quite frequently and many people who experience these types of miscarriage don’t know they miscarried at all, it is unlikely that a single early miscarriage occurring before it’s even detected has implications for long-term fertility. Many people who miscarry, even later into pregnancy and multiple times, can go on to have healthy pregnancies in the future (2,6,8).

If you’re nervous that you might be pregnant and want to know if your bleeding is a miscarriage or a normal period, you should take a pregnancy test or visit your healthcare provider.

When to take a pregnancy test

If you have a late period, are trying to get pregnant, or are worried you are pregnant, and you’re unsure if you should take a pregnancy test, consider your risk of pregnancy:

You are at risk of pregnancy if you had unprotected penis-in-vagina sex or had a high risk of sperm touching your genitals. The risk varies over the course of your cycle.

For people with regular cycles (for example, the time between periods rarely varies by more than a couple days),

sperm exposure poses the highest risk of pregnancy from around the middle of the cycle to about 2 weeks before your anticipated period, because this is when most people ovulate. This is only true in general, and it might not be reflective of any given cycle, so you shouldn’t rely on this rough estimate for pregnancy prevention.

(Note that the ovulation day and fertile window displayed in Clue is only an estimate — your actual day of ovulation might have different timing, which can vary cycle-to-cycle along with the start date of your period.)

Sperm exposure towards the beginning or the end of the cycle in general poses less risk of pregnancy, because it’s less likely that a person ovulated close to or during those times.

You should take a pregnancy test or contact your healthcare provider if your period is nine or more days late.

If you want to take a pregnancy test sooner, it’s generally recommended to wait at least two weeks after your estimated ovulation day, or around when you expect to get your period. For the most accurate results, it’s best to wait a few days after your expected period. Some pregnancy tests advertise that you can take them earlier than that, but the earlier you take a test the less accurate it is (9). It’s up to you if you want to take it sooner.

If you have an irregular cycle (i.e. you don’t know when your period is going to come, and the difference between your longest cycle and shortest cycle is more than 7–9 days),

unprotected sex or exposure of sperm on your genitals at most times represents a higher risk because it’s harder to estimate when you were exposed. You can take a pregnancy test about two weeks after your last unprotected sexual encounter, though waiting a few days longer will help improve the accuracy of the results.

(We talk more about how pregnant tests work here.)

If you are using an active form of natural birth control (aka fertility awareness based methods or natural family planning) or are tracking fertility signs for body literacy, you will have a better idea of your timing of ovulation and can use that to assess your risk of pregnancy.

(Remember, any form of unprotected sex at any time represents a risk of sexually transmitted infections.)

If you know you are pregnant and begin bleeding

it is important to contact your healthcare provider. Bleeding during early pregnancy is common and isn’t necessarily a sign of a miscarriage (10), but it’s good to let them know what’s going on.

If you experience abnormal bleeding, severe pain from your pelvis to your shoulders, and are feeling weak or are fainting, you should seek medical care immediately (11).

These could be signs of an ectopic pregnancy (when a fertilized egg attaches and grows somewhere other than the uterus, most commonly in the fallopian tube) (11).

Ectopic pregnancies are life-threatening and should be treated as medical emergencies.

Article was originally published on Nov. 7, 2017.