What is miscarriage?

Pregnancy loss is the spontaneous end of a pregnancy before 20 weeks’ gestation. Miscarriage, sometimes called spontaneous abortion, is a type of pregnancy loss. However, it specifically refers to the loss of a pregnancy that was clinically confirmed by ultrasound or pathology.^i,ii

Here are some other terms worth knowing:

• ‍Chemical pregnancy or biochemical pregnancy (CP): A CP is a pregnancy that is diagnosed by a positive urine or blood test, but that ends (meaning the 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 it a different category of loss.
• ‍Early pregnancy loss (EPL): EPL is a miscarriage that occurs in the first trimester, or up to 12 weeks, six days gestational.^iv
• ^‍Stillbirth: Also known as late pregnancy loss, stillbirth is defined as fetal loss at a gestational age greater than 20 weeks.^v
• ^‍Recurrent pregnancy loss: Recurrent 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

How common are miscarriages?

Miscarriages occur in approximately 10 to 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 the 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 females 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 eight and 14 weeks, the risk of pregnancy loss decreases to around 2.5 percent, and is reduced further to 1.4 percent after 14 weeks.^x Thus, miscarriages are most common earlier in pregnancy, and only 1 to 5 percent of pregnancy losses occur between weeks 13 to 19 gestation, while 0.3 percent occur between weeks 20 to 27 gestation.^xi

What can cause a miscarriage?

The most common cause of miscarriage is a genetic abnormality within the embryo, which accounts for 50 to 70 percent of all early pregnancy losses.^xii The risk of this type of early pregnancy loss increases with age, ranging from 10 to 15 percent in females under 35 to more than 50 percent in females 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. Trisomy accounts for more than 60 percent of miscarriages with genetic abnormalities.^xiv

Miscarriages also happen due to other causes:^xv

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

Here are some common risk factors for miscarriage:^xvi

• 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 less than 18.5 or greater than/equal to 30 kg/m2 is associated with the greatest risk)
• Previous miscarriage
• Smoking
• Alcohol use
• Stress

Of these, older maternal age is the most significant risk factor for pregnancy loss.^xvii

Can a miscarriage be prevented?

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

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 females 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 individuals with three or more consecutive miscarriages.^xviii

AAnother factor associated with miscarriage, especially in the second trimester, is reduced cervical length (called cervical incompetence, cervical insufficiency, or incompetent cervix).

Cervical incompetence can sometimes be treated with an intervention known as a cervical cerclage. The process 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.^xix

A recent study showed that in patients with recurrent miscarriage, the risk of future miscarriage is higher in females 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.^xx

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.^xxi

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

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 females, and the risk of pregnancy loss is higher in individuals with heavy bleeding compared to light bleeding.^xxiii Amongst females 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.^xxiv

Importantly, vaginal bleeding in pregnancy does not always indicate a miscarriage. There are other causes of vaginal bleeding during pregnancy:^xxv

• 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 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 A septic miscarriage is a surgical emergency and represents a pregnancy that is not viable.

Miscarriages can also occur with no symptoms at all. This scenario 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 individuals presenting for routine screening ultrasound at 10 to 13 weeks’ gestation had an asymptomatic non-viable pregnancy (missed abortion).^xxviii

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

How do doctors diagnose a miscarriage?

In general, if a pregnant person experiences heavy bleeding (soaking one to two pads an hour for at least two hours), they 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:

• A gestational sac with a mean diameter of greater than or equal to 25 mm with no embryo seen (known as an anembryonic pregnancy)^xxx‍
• An embryonic crown-rump length (CRL; overall length of the embryo) of greater than or equal to 7 millimeters and no fetal heartbeat.^xxxi Fetal heart activity should be seen after six weeks’ gestation.
• No embryo with heartbeat two 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^xxxii

If the ultrasound shows a viable pregnancy but there is a suspicion of miscarriage due to heavy bleeding or pain, a repeat ultrasound can be completed in seven to 10 days. If a pregnancy is seen on ultrasound outside of the uterus, an ectopic pregnancy is diagnosed.^xxxiv 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.^xxxv

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 an 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 3,000 IU (formerly 1,500 IU), an intrauterine pregnancy should be visible on ultrasound. This 3,000 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.^xxxvi

After a miscarriage is diagnosed, hCG levels are usually checked weekly and trended to zero. This monitoring 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 seven to 60 days.^xxxvii

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.

Expectant management

Expectant management involves waiting seven to 14 days for the pregnancy tissues to pass spontaneously. At eight weeks' gestation, expectant management has an approximately 80 percent success rate.^xxxviii Success of expectant management may be slightly lower in the case of anembryonic pregnancies (where no embryo is seen) at around 70 to 75 percent.^xxxix,xl,xli The benefit of expectant management is that patients can pass the pregnancy in the comfort of their homes and can avoid medications or invasive procedures. The downside to expectant management is that the timing of the passed tissue is hard to predict.

Medical management

If the patient prefers medication as an option for miscarriage treatment, or if the patient is not spontaneously passing the remaining 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 four to six hours.^xlii 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 to 90 percent of cases.^xliii 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 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 process is completed under sedation or general anesthesia.^xliv The benefits of D&C are a high success rate (approaching 99 percent) and lack of pain given that the procedure is done under anesthesia.^xlv Additionally, the process 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.^xlvi

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

What to expect after a miscarriage?

Miscarriage can be a distressing event for pregnant individuals, and approximately 20 percent of people 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.^xlviii

Patients with certain blood types may require special medication following a miscarriage, which 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.^xlix If RhoGAM is not given, patients can develop antibodies that can attack fetal red blood cells in future pregnancies, leading to the pregnancy complication of fetal anemia.

When to start trying again after miscarriage? 

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

A 2018 study followed 514 female patients who had recently miscarried. The researchers found that individuals who conceived within three months of their previous miscarriage had a lower chance of miscarrying (7.3 percent) compared to those who conceived six to 18 months later (22.1 percent).^l This study suggests that, generally, 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.^li

Conclusion

Though miscarriage is relatively common, it can be a disappointing and traumatic experience. Thankfully, for anyone hoping to have a subsequent viable pregnancy, the risk of recurrent miscarriage is low. Individuals 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 who is concerned about pregnancy loss or is thinking about conceiving again after miscarriage should speak with a doctor to determine appropriate treatment.