What is miscarriage?

Pregnancy loss is the spontaneous end of a pregnancy before 20 weeks’ gestation. Miscarriage is a type of pregnancy loss, but specifically refers to the loss of a pregnancy that was clinically confirmed by ultrasound or pathology.  A miscarriage is also known as a spontaneous abortion.^i,ii A chemical or biochemical pregnancy (CP) is a pregnancy diagnosed by a positive urine or blood test, but that ends (urine or blood test becomes negative) before the pregnancy can be visualized on ultrasound or pathology at around 6 weeks gestation.ⁱⁱⁱ Some providers and studies include chemical pregnancies in their definition of miscarriage, while others consider this a different category of loss.  An early pregnancy loss (EPL) is a miscarriage that occurs in the first trimester, or up to 12 weeks, 6 days gestational age.^iv Stillbirth, also known as late pregnancy loss, is defined as fetal loss at a gestational age greater than 20 weeks.^v

Recurrent pregnancy loss is defined as the occurrence of two or more consecutive miscarriages.^vi Less than 5 percent of people have two or more losses, and less than 1 percent will have three or more losses.^vii

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How common are miscarriages? 

Miscarriages are estimated to occur in approximately 10-30 percent of all pregnancies.^viii The reported prevalence of miscarriage is variable between studies, but research consistently shows that the risk of miscarriage increases with age.

The rate of pregnancy loss and miscarriage decreases as pregnancy progresses. The risk of first trimester (early pregnancy) loss, including biochemical pregnancy, is around 30 percent. When biochemical pregnancy losses are not considered, there is an approximately 15 percent risk of clinical miscarriage before 13 weeks’ gestation.^ix These risks are higher in older women with an approximately 20 percent risk of first trimester clinical miscarriage at age 35, 40 percent at age 40, and 80 percent at age 45. Between 8 and 14 weeks, the risk of pregnancy loss decreases to around 2.5 percent and then is reduced further to 1.4 percent after 14 weeks.^x  Thus, miscarriages are most common earlier in pregnancy, and only 1-5 percent of pregnancy losses occur between weeks 13-19 gestation, while 0.3 percent occur between weeks 20-27 gestation.^xi

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What can cause a miscarriage? 

The most common cause of miscarriage is a genetic abnormality within the embryo, which accounts for 50-70 percent of all early pregnancy losses.^xii The risk of this type of early pregnancy loss increases with age, ranging from 10-15 percent in women under 35 to more than 50 percent in women over the age of 40.^xiii The most frequently detected genetic abnormality associated with miscarriage is trisomy, in which the embryo has an extra chromosome in each cell. Of miscarriages with genetic abnormalities, trisomy accounts for more than 60 percent of these cases.^xiv

Miscarriages also occur due to other causes, including^xv:

• Parental chromosomal abnormalities
• Autoantibodies
• Immune cell dysfunction
• Blood clotting disorders (thrombophilias)
• Thyroid dysfunction
• Uterine abnormalities
• Maternal alcohol consumption  

Risk factors for miscarriage include younger maternal age (under 20 years old), older maternal age (over 35 years old), older paternal age (over 40 years old), very low or high body mass index (BMI <18.5 or >=30 kg/m² associated with the greatest risk), previous miscarriage, smoking, alcohol use, and stress. Of these, older maternal age is the most significant risk factor for pregnancy loss.^xvi

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Can a miscarriage be prevented?

Most miscarriages cannot be prevented. However, there are interventions that may help decrease the risk of miscarriage for certain patients.

With repeated miscarriages, a hormone called progesterone has been shown to reduce the rate of miscarriage for some patients. A review of clinical trials including 2 556 women found that progesterone supplementation may lower the risk of miscarriage from 27.5 percent to 20.1 percent, but the benefit was only seen for those with three or more losses.^xvii

Another factor associated with miscarriage, especially in the second trimester, is reduced cervical length (called cervical incompetence, cervical insufficiency, or incompetent cervix), which can sometimes be treated with an intervention known as a cervical cerclage. This involves placing stitches in the cervix to keep it closed, allowing the pregnancy to continue to develop. This intervention is not useful for preventing first trimester miscarriages but may be useful in preventing second trimester miscarriages and pre-term delivery.^xviii

A recent study showed that in patients with recurrent miscarriage, the risk of future miscarriage is higher in those with a BMI in the obese range, meaning greater than 30 kg/m². Therefore, weight loss prior to conception may be beneficial in preventing miscarriage.^xix

People with endocrine disorders such as diabetes and hypothyroidism are also at an increased risk of miscarrying. Proper medical management of these conditions has also been shown to prevent pregnancy loss.^xx

Bed rest has not been shown to be effective in preventing miscarriage.^xxi

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What are the symptoms of miscarriage? 

Vaginal bleeding, especially associated with cramping, is the most common symptom of miscarriage. Various studies have estimated that vaginal bleeding affects anywhere from 7 to 25 percent of pregnant women, and the risk of pregnancy loss is higher in those with heavy bleeding compared to light bleeding.^xxii Amongst those with first trimester bleeding, about 70 percent only have a single episode of bleeding, while 20 percent have two episodes and 10 percent have three or more episodes.^xxiii

Importantly, vaginal bleeding in pregnancy does not always indicate a miscarriage. Other causes of vaginal bleeding during pregnancy include:^xxiv

• Normal placentation
• Subchorionic hematoma (SCH), in which blood pools behind the placenta, similar to a small bruise
• Ectopic pregnancy, in which the embryo implants in a location outside the uterus (most commonly in the fallopian tubes)
• Gestational trophoblastic disease, a rare condition in which cancerous or non-cancerous tumor cells are present with a normal or abnormal pregnancy

A study by Hinkle et al (2016) of 797 pregnant women showed that nausea and vomiting in pregnancy were associated with a lower risk of pregnancy loss.^xxv

A septic miscarriage (septic abortion) describes a miscarriage accompanied by a uterine infection. This type of miscarriage will present with a fever in addition to cramping and vaginal bleeding.^xxvi This is a surgical emergency and represents a pregnancy that is not viable.  

It is also possible for a miscarriage to have no symptoms at all. This is clinically known as a missed miscarriage or missed abortion. Patients may only become aware that they have miscarried during an ultrasound examination performed at a routine prenatal appointment.^xxvii In one study of 17 870 patients, around 3 percent of those presenting for routine screening ultrasound at 10-13 weeks’ gestation had an asymptomatic non-viable pregnancy (missed abortion).^xxviii

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How do doctors diagnose a miscarriage? 

In general, if a woman is pregnant and bleeding heavily (soaking one to two pads an hour for at least two hours), she should be seen by a doctor for evaluation for a miscarriage.  

In cases with a clinically confirmed pregnancy, a transvaginal and pelvic ultrasound will be performed as part of routine prenatal care or if miscarriage is suspected. Miscarriage is diagnosed based on specific radiologic signs seen on ultrasound, including:

• Embryonic crown-rump length (overall length of the embryo) of ≥ 7 millimeters and no fetal heartbeat.^xxix Fetal heart activity should be seen after 6 weeks’ gestation.  
• Gestational sac mean diameter of ≥ 25 mm with no embryo seen (known as an anembryonic pregnancy).^xxx
• No embryo with heartbeat 2 weeks or more after an ultrasound that showed a gestational sac without a yolk sac.  
• No embryo with heartbeat seen 11 days or more after an ultrasound showed a gestational sac with a yolk sac.^xxxi

If the ultrasound shows a viable pregnancy but there is a suspicion of miscarriage due to bleeding or pain, a repeat ultrasound can be completed in 7-10 days. If a pregnancy is seen on ultrasound outside of the uterus, an ectopic pregnancy is diagnosed.^xxxii Ectopic pregnancies are not viable pregnancies and usually require medical or surgical intervention.

To assist with a miscarriage diagnosis, a doctor may perform a speculum examination, which is similar to the examination done during a Pap test. A miscarriage may be diagnosed if the cervix is open and tissues from the pregnancy (known as products of conception) are present at the opening of the cervix.^xxxiii‍

The main hormone detected in pregnancy tests is beta-hCG. In the evaluation of miscarriage, b-hCG blood tests are performed. In early pregnancy, b-hCG level is expected to rise by at least 53 percent every two days, indicating a normally developing pregnancy. Thus, serial b-hCG tests every two days or at regular intervals are sometimes performed if there is concern for miscarriage. If the b-hCG is not rising as expected, a miscarriage may be suspected. If blood hCG has decreased from a previous reading, a successful pregnancy is unlikely.  

In very early pregnancy, serial b-hCG tests are often the only option to confirm a miscarriage because an embryo at this stage is too small to see on ultrasound. Later in pregnancy, b-hCG tests may be ordered in combination with an ultrasound to distinguish between a viable or nonviable pregnancy.  Once a patient’s blood b-hCG level reaches 3000 IU (formerly 1500 IU), an intrauterine pregnancy should be visible on ultrasound. This 3000 IU value is known as the “discriminatory zone.” If the B-hCG level is above the discriminatory zone and there is no pregnancy in the uterus, there is a concern for ectopic pregnancy.^xxxiv‍

After a miscarriage is diagnosed, hCG levels are usually checked weekly and trended to zero. This helps to ensure there is no remaining fetal and pregnancy tissue left in the uterus. The time for beta-hCG to return to zero following a miscarriage is variable and can take between 7-60 days.^xxxv

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What are the treatment options for a miscarriage?

Miscarriage treatments include expectant management, medication management, and surgical management. The specific treatment selected depends on the clinical scenario and the patient’s personal preference.

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Expectant management

Expectant management involves waiting 7-14 days for the pregnancy tissues to pass spontaneously. At 8 weeks gestation, expectant management has an approximately 80 percent success rate.^xxxvi Success of expectant management may be slightly lower in the case of anembryonic pregnancies, around 70-75 percent.^{xxxvii,xxxviii,xxxix} The benefit of expectant management is that patients can pass the pregnancy in the comfort of their own home and can avoid medications or invasive procedures. The downside to expectant management is that timing of passage of the pregnancy is hard to predict and 20-30 percent of women will not pass the tissue on their own.

Medication management  

If the patient prefers medication as an option for miscarriage treatment, or if the patient is not spontaneously passing remaining pregnancy tissue, medication can be prescribed to help accelerate the process. Misoprostol, a prostaglandin medication, can be inserted vaginally or taken orally to stimulate uterine contractions and help pass the remaining tissue. Mifepristone may also be given with misoprostol to help improve success rates. Most patients pass pregnancy tissue within 24 hours of taking misoprostol with/without mifepristone, with most patients experiencing cramping and bleeding in the first 4-6 hours.^xl Misoprostol can be re-dosed 24 hours after the first dose if bleeding does not occur.  

The benefit of medical management is a higher success rate compared to expectant management and the timing of pregnancy passage is more predictable. In the first trimester, medical management of miscarriage is successful in 85-90 percent of cases.^xli In these cases, patients can avoid surgical intervention. The downside of medical management is that passing the pregnancy is painful and often takes several hours. Additionally, chromosomal testing of pregnancy tissue may not be able to be performed unless the patient brings the pregnancy tissue into the office.  

Surgical management

Surgical procedures can also be performed to treat miscarriage. The most commonly used procedure for this purpose is dilation and curettage (D&C). During a D&C, the cervix is dilated, and the contents of the uterus are removed with a suction catheter and small instrument known as a curette. This is done under sedation or general anesthesia.^xlii The benefits of D&C are a high success rate (approaching 99 percent) and the lack of pain given the procedure is done under anesthesia.^xliii Additionally, the procedure is quick (less than an hour), and pregnancy tissue can be sent for genetic testing. The downsides of a D&C include the need for a procedure in the operating room, risks of anesthesia (although low), and the rare risks of surgical complications such as bleeding, infection, uterine perforation, and uterine scarring.^xliv  

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If pregnancy loss occurs in the second trimester (after 12 weeks), the procedure utilized to treat the miscarriage is called a dilation and evacuation (D&E). D&E is similar to a D&C but can take longer, requires different instruments, and has slightly increased surgical risks.^xlv

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What to expect after a miscarriage? 

Miscarriage can be a distressing event for pregnant women, and approximately 20 percent of women who experience a miscarriage develop depression or anxiety. Patients experiencing mood changes following a miscarriage should be seen by a doctor, who can provide counseling, referral for therapy, or medication.^xlvi‍

Patients with certain blood types may require special medication following a miscarriage; this is one reason that maternal blood type is routinely assessed in patients who are miscarrying. Patients with blood types that are rhesus negative require a medication called RhoGam (Rh immunoglobulin) to help prevent complications in future pregnancies.^xlvii If Rhogam is not given, patients can develop antibodies which can attack fetal red blood cells in future pregnancies, leading to the pregnancy complication of fetal anemia.

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When to start trying again after miscarriage? 

Deciding when to start trying to conceive after experiencing miscarriage is a highly personal decision that depends on a number of physical and emotional factors.  

A 2018 study followed 514 female patients who had recently miscarried. The researchers found that women who conceived within three months of their previous miscarriage had a lower chance of miscarrying (7.3 percent) compared to those who conceived 6-18 months later (22.1 percent).^xlviii This study suggests that, generally speaking, there are no physical contraindications to trying to conceive again soon after miscarriage.  

Given the potential impact of miscarriage on mental health, it is important to consider emotional readiness to conceive again in addition to physical readiness.^xlix

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Conclusion

Experiencing a miscarriage can be disappointing and traumatic but is quite common. For those hoping to have a subsequent viable pregnancy, the risk of recurrent miscarriage is low. Women can attempt to conceive again shortly after a miscarriage if the loss was uncomplicated, although individual factors regarding physical and mental wellbeing must be taken into consideration prior to attempting conception again. Anyone concerned about a pregnancy loss or who is thinking about conceiving again after a pregnancy loss should speak with her doctor to determine appropriate treatment.