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Understanding Miscarriage

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Nobody Wants to Be Here

First off, we're sorry you're here. Nobody wants to be in a position where they need information on miscarriage, and the fact that you're reading this probably means that you or someone you care about is going through a physical and emotional trauma.

Surprisingly, miscarriage requires you to make many important decisions quickly, often while still in shock. This guide was built to help shed light on the available options so that informed decisions can be made.

A Quick Note on Language

The language and terminology around miscarriage leaves a lot to be desired. Words like “miscarriage,” “pregnancy loss,” “failed pregnancy,” or phrases like “lost the baby” all seem to assign fault to the person carrying the pregnancy. We understand that these phrases can be hurtful.

We’ll get into this more later when we discuss the reasons for miscarriage, but it’s important enough to repeat: in all likelihood, you did nothing to cause this. Most people have feelings of guilt—imagining that maybe lifting something heavy, having sex, or getting into an argument caused this to happen. The terminology fails to acknowledging that none of these events cause miscarriage.

Defining Miscarriage

A clinical miscarriage is the loss of a pregnancy that was visible on ultrasound. This is in contrast to a very early miscarriage, where there was a positive pregnancy test, but the pregnancy couldn’t be seen on ultrasound. Doctors refer to this type of loss as a chemical pregnancy.

Miscarriage is by far the most common complication of pregnancy. The Zinnaman study, which very closely followed early pregnancies and losses, found that 30% of early pregnancies were lost.

There are a few ways that miscarriage can be diagnosed, which we’ll cover next.

Is This a Miscarriage?

A miscarriage can happen with a range of noticeable symptoms or none at all. In early pregnancy, symptoms that could signal miscarriage include bleeding, severe cramping, or pain. Remember, these symptoms are just signs of what could be—it’s certainly possible for a pregnancy to continue even with these symptoms.

A doctor might suspect a miscarriage—or an ectopic pregnancy—if there is a drop in the levels of the pregnancy hormone hCG (which is present in the blood) or if the hCG level is very low. This is more commonly noted for people who have conceived via fertility treatments, as most pregnancies that happen spontaneously aren’t monitored with several hCG blood tests or betas.

Having hCG numbers that aren’t very high or aren’t rising quickly might make a doctor suspicious that a miscarriage is happening, but this typically isn’t enough to diagnose a miscarriage. In short, you shouldn't make a diagnosis based on a single blood value. The data around how quickly hCG levels should increase is more nuanced than might be generally recognized.

There are certain milestones that can be seen on ultrasound as a pregnancy progresses. If an ultrasound reveals the embryo hasn't developed as typically expected, it might indicate a miscarriage. For example, if your last menstrual cycle indicates you’re likely seven weeks gestation but a heartbeat isn’t detected, it might raise flags that a pregnancy loss has occurred. However—and this is really important—just using the time from your last period can be unreliable, so more information is needed in addition to that single datapoint to make a diagnosis.

Beta & HCG Numbers Explained

Interpreting ambiguous beta or hCG tests can be incredibly stressful. It’s not quite as clear cut as the standard wisdom that “the beta test needs to show hCG levels doubling every 48 hours.”

The first factor that may impact test results comes with the lab—with lab error or differences between laboratories both potentially affecting results. There are also circumstances that may make the numbers look like they aren't increasing the way they should, but there really is a healthy pregnancy.

For example, vanishing twin syndrome— where a pregnancy starts with two embryos, but by the time you see anything on ultrasound, there's only one — could lead the hCG levels to rise in unexpected ways.

Another misconception to highlight is that the rise in hCG doesn't always continue at a particular rate. Typically hCG rises quickly early on, but then will plateau and start to fall at around 10 weeks.

According to a study of 250+ women who presented with pain at an emergency room—and ultimately did have a confirmed intrauterine pregnancy—the actual and assumed rate of “beta growth” was correlated with how high the initial beta number was. If a beta number started off lower, the 48 hour increase was higher, as seen in the table below.

So if a woman had 100 on her initial hCG test, her pregnancy may still be viable if two days later it grew by ~80%. However, if a woman had 5000 on her initial hCG test, her pregnancy may still be viable if it only grew by ~30% two days later. Though not clinically significant, if the beta numbers are low to start with, race can be a factor in the expectation of beta growth over time.

Finally, it’s important to recognize that the “beta number needs to show hCG levels doubling every 48 hours” guideline comes from studies with large numbers of participants. The increase of beta growth doubling is the average over time from many sets of data points. So on an individual patient basis, making a miscarriage diagnosis based on one set of blood tests may be ill-advised. Beta testing does give important information, but it’s just one part of the overall picture while assessing a pregnancy’s viability.

Ultrasound to Diagnose Miscarriage

Ultrasound can be a critical tool for monitoring the health of a pregnancy, and for helping to diagnose issues like miscarriage and ectoptic pregnancy. In this lesson we’ll help shed light on the details of how ultrasound can be used to confirm or diagnose a miscarriage or ectopic pregnancy.

Ultrasound to Locate the Pregnancy

If there are symptoms like severe pain, or if the levels of hCG found in blood tests are lower than expected, it’s crucial to have an ultrasound to locate the pregnancy.

If an embryo is located in the uterus, there’s no need to rush a diagnosis. If the pregnancy is located outside the uterus, it’s called an ectopic pregnancy. For example, if the ultrasound reveals the pregnancy is in the fallopian tube, more specifically called a tubal pregnancy, that will require immediate action because it is a potentially life-threatening situation.

Later we’ll discuss the options for how to handle an ectopic pregnancy using either medication or surgery.

Ultrasound to Diagnose Miscarriage

Transvaginal ultrasounds are used during early pregnancy. Developmental stages of an embryo and measurements are observed at different points in time. If some of these measurements or stages are off, it can signal a potential miscarriage. For example, red flags are raised if an embryo doesn’t have expected growth by a certain point in time or if the embryo has grown but no heartbeat is detected.

A heartbeat should be seen shortly after six weeks gestation. But this is usually presumed based on the timing of the most recent menstrual period—which can be unreliable to truly diagnose a miscarriage.

If you’ve had multiple ultrasounds, this measure of time can be more helpful. For example, if a first ultrasound showed a gestational sac with a yolk sac, and 11 days later, a second ultrasound doesn’t show a heartbeat, this would reveal the embryo didn’t develop properly, and would diagnose a miscarriage.

A study by Peter Doubilet published in the New England Journal of Medicine looked into the measurements that should raise suspicion of miscarriage versus those that should count as a definitive diagnosis of miscarriage.

Doubilet found that some indicators doctors had relied on to diagnose miscarriage carried a risk of "false positives," meaning that there was a risk they'd call something a miscarriage when it wasn't. Doubilet's paper focused on setting criteria that eliminated the risk of false positives."

Examples of ultrasound measurements that do definitively show that a miscarriage has happened:

  • A gestational sac diameter of 25mm but without being able to see an embryo
  • A “crown to rump” length measuring an embryo at 7mm but without a detected heartbeat

There are also time-based criteria of things that should be seen on ultrasound based on a certain point in the pregnancy.

Repeating Ultrasound to Confirm Miscarriage

After about six weeks of gestation (six weeks + two days), a heartbeat can be detected on ultrasound. If a pregnancy is suspected to be at least that far along, but no heartbeat can be seen with ultrasound, that could indicate miscarriage.

If it appears on ultrasound that there might have been a miscarriage—for example, if someone is believed to be eight weeks pregnant but there is no heartbeat detected on ultrasound—it’s important to have this confirmed by a subsequent follow-up ultrasound.

It’s always possible that ovulation might have happened later than estimated, which would transform a seemingly alarming finding of no heartbeat into a normal level of development for that time.

There is not a reliable study specifically on how often this happens, but there have been clinical reports of patients referred for a D&C surgery following a miscarriage diagnosis, only to have a heartbeat found on re-ultrasound before the surgery. It’s always a good idea to advocate for yourself and ask that an ultrasound be repeated following a diagnosis of miscarriage. If nothing else, a second ultrasound will make everyone involved 100% sure of the diagnosis, and not make an already difficult situation harder by injecting doubt.

If a heartbeat is detected on re-ultrasound, the pregnancy should be monitored as normal. If no heartbeat is detected, there will be a decision of how to handle the miscarriage: naturally, with medication, or surgically.