Spontaneous abortion is the loss of pregnancy naturally before twenty weeks of gestation. Colloquially, spontaneous abortion is referred to as a ‘miscarriage’ to avoid association with induced abortion. Early pregnancy loss refers only to spontaneous abortion in the first trimester. However, the first trimester is when most spontaneous abortions occur. Therefore, in this article, these three terms will be used interchangeably.
Early pregnancy loss takes many different forms. In missed abortion, there is asymptomatic or ‘missed’ death of the embryo or fetus without sufficient uterine contractions to push out the products of conception. In contrast, threatened abortion is characterized by symptomatic, ‘threatened’ expulsion of the products of conception, yet the cervical os remains closed, and the embryo or fetus remains viable. Inevitable abortion is distinguished from threatened abortion by the presence of an open cervical os, indicating the ‘inevitable’ passage of the conception products. In incomplete abortion, there is an ‘incomplete’ passage of the products of conception through the cervical os.
Complete abortion is defined as a ‘complete’ passage of all conception products. Recurrent abortion is defined as three or more consecutive pregnancy losses. Septic abortion can occur when retained products of conception become infected, which usually occurs in the setting of non-sterile induced abortion.
In 50% of cases, early pregnancy loss is believed to be due to fetal chromosomal abnormalities. Advanced maternal age and previous early pregnancy loss are the most common risk factors. For example, the incidence of early pregnancy loss in women 20-30 years of age is only 9 to 17%, while the incidence at 45 years of maternal age is 80%. Other risk factors include alcohol consumption, smoking, and cocaine use.
Several chronic diseases can precipitate spontaneous abortion, including diabetes, celiac disease, and autoimmune conditions, particularly anti-phospholipid antibody syndrome. Rapid conception after delivery and infections, such as cervicitis, vaginitis, HIV infection, syphilis, and malaria, are also common risk factors. Another important risk factor is exposure to environmental contaminants, including arsenic, lead, and organic solvents. Finally, structural uterine abnormalities, such as congenital anomalies, leiomyoma, and intrauterine adhesions, have been shown to increase the risk of spontaneous abortion.
Vaginal bleeding before twenty weeks of gestation occurs in up to 20% of pregnancies, and 50% of these cases will have a spontaneous abortion. Overall, 10-20% of clinically recognized pregnancies will end in early pregnancy loss. However, these statistics likely underestimate the true incidence of spontaneous abortion, as many miscarriages occur before a mother realizes she is pregnant and is simply mistaken as heavy, late menses. As a result, the true incidence of spontaneous abortion may be closer to 30%.
Complications of early pregnancy loss include hypovolemic shock due to excessive hemorrhage and septic abortion due to infection of retained conception products. Fortunately, these complications are rare, and complication rates are similar for expectant, medical, and surgical management. As a result, the prognosis of spontaneous abortion is remarkably good. However, hemorrhage and infection due to miscarriage can contribute to maternal mortality, especially in low-income countries, where the social determinants of health decrease access to high-quality obstetrical care.
Symptoms of spontaneous abortion depend on the type. A missed abortion is either asymptomatic or accompanied by a regression of the natural symptoms and signs of normal pregnancy. Threatened, inevitable, incomplete, and complete abortions are all associated with abdominal-pelvic cramping and vaginal bleeding. In addition to these symptoms, septic abortion is often accompanied by fever, purulent cervical or vaginal discharge, tachycardia, and hypotension. An attempt should be made to quantify the amount of bleeding, as hemorrhage greater than typical menses often suggests early pregnancy loss. When there is significant bleeding, patients can exhibit symptoms and signs of hypovolemia, even in the absence of sepsis.
The first day of the last menstrual period and findings on any prior ultrasounds should be determined to establish the gestational age and location of the pregnancy. An abdominal exam should be performed to assess for peritoneal signs that might indicate a ruptured ectopic pregnancy or extra-uterine extension of a septic abortion. Lastly, a pelvic exam is central to the evaluation of suspected miscarriage. It should include both speculum-facilitated visualization of the cervix and a bimanual examination to assess for cervical motion tenderness that may indicate a septic abortion or an adnexal mass that may herald ectopic pregnancy.
Further evaluation of miscarriage also depends on the type suspected based on history and physical exam. As a missed abortion has no reliable symptoms or signs, it can only be diagnosed by measurement of beta-human chorionic gonadotropin (beta-hCG) levels and pelvic ultrasound. A beta-hCG level is useful initially, as it helps determine the likelihood of intrauterine pregnancy. For example, when the beta-hCG level is more than 1,500-3,000 mIU/mL (the discriminatory level), intrauterine pregnancy should be evident on transvaginal ultrasound. If an intrauterine pregnancy is not seen on ultrasound with a beta-hCG above the discriminatory level, either early pregnancy loss or ectopic pregnancy should be suspected.
In the setting of a viable pregnancy, beta-hCG levels increase at a relatively predictable rate. However, as the beta-hCG level increases, its rate of rising gradually decreases until reaching a plateau at ten weeks gestation. For example, an initial beta-hCG level of less than 1500 will increase by 50% over 48 hours, while an initial level greater than 3000 will only increase by 33% over the same period.
The events of early pregnancy follow a predictable pattern and any variation from this sequence concerns spontaneous abortion. For example, a gestational sac with a mean diameter of at least 25 mm should contain a viable embryo, and an embryo with a crown-rump length of at least 7 mm should demonstrate detectable cardiac activity. Besides, the development of the yolk sac follows the appearance of the gestational sac and is usually accompanied by the presence of an embryo with cardiac activity.
Therefore, when there is evidence of prior intrauterine pregnancy, spontaneous abortion can be diagnosed if the mean gestational sac diameter is greater than or equal to 25 mm on pelvic ultrasound but contains no embryo or if the crown-rump length of the embryo is greater than or equal to 7 mm, but there is no cardiac activity. Early pregnancy loss can also be diagnosed if there is no embryo with cardiac activity at least 14 days after prior ultrasound demonstrated a gestational sac or at least 11 days after a previous ultrasound revealed a gestational sac with a yolk sac. However, some ultrasound findings, such as an embryonic heart rate of fewer than 85 beats per minute, are suspicious but not diagnostic for early pregnancy loss. When the diagnosis of spontaneous abortion is uncertain, trending beta-hCG levels every 48 to 72 hours and repeating the pelvic ultrasound in 7-10 days are recommended.
Threatened abortion can be diagnosed in the setting of cramping and vaginal bleeding but with a closed cervical os on exam and evidence of a viable intrauterine pregnancy on ultrasound. Inevitable abortion is diagnosed in the presence of cramping, vaginal bleeding, an open cervical os on the physical exam but no passage of the products of conception. The intrauterine pregnancy may be either viable or nonviable on ultrasound. Incomplete abortion can be diagnosed in the instance of cramping, bleeding, an open cervical os, and partial passage of conception products. Retained products of a nonviable pregnancy will be evident on ultrasound. Complete abortion is diagnosed in the case of resolving cramp and bleeding, either an open or closed cervical os and no intrauterine conception products on ultrasound.
Septic abortion is diagnosed when cramping, and bleeding is followed by purulent cervical or vaginal discharge, fever, and an open or closed cervical os. If an induced abortion was performed with poor technique, then pelvic ultrasound may reveal retained conception products, exudative fluid, an extra-uterine extension of the infection, or uterine perforation.
Besides beta-hCG measurement and ultrasound, a hemoglobin and hematocrit level should be obtained to rule out acute blood loss anemia. If unknown, maternal blood type and Rh status should be determined to prepare for possible blood transfusion or administration of Rh (D)-immune globulin. Since spontaneous abortion can be precipitated by infection, wet mount examination and screening for gonorrhea and chlamydia should also be considered. This is especially important in septic abortion, where cultures of urine, blood, endocervical secretions, and evacuated conception products are recommended.
To some extent, the management of spontaneous abortion also depends on the type. However, expectant, medical, and surgical management is generally shown to be equally effective. Two notable exceptions are excessive bleeding and infection, in which case, surgical management is preferred. Also, expectant management of missed abortion demonstrates a variable success rate of 25 to 76%. Therefore, surgical or even medical management of missed abortion is generally accepted as the preferred method of management. Threatened and inevitable abortion can be managed expectantly unless the patient desires medical or surgical intervention. Incomplete abortion can also be managed expectantly. However, it may take up to eight weeks for 80% of women to experience a complete abortion with expectant management alone. As a result, medical management of incomplete abortion is becoming more prevalent.
The conventionally accepted regimen for medical management consists of misoprostol 800 mcg vaginally, with a repeated dose if needed any time from three hours to seven days after the first dose. Premedication with mifepristone 200 mg orally 24 hours before the first dose of misoprostol may result in a higher success rate than misoprostol alone. Surgical management consists of dilation and suction curettage with sharp curettage, as needed, in either the operating room or office setting. There is evidence that suction curettage alone, without sharp curettage, is sufficient and decreases the risk of intrauterine adhesions, as long as there is reasonable certainty that the uterus is empty. Due to a lack of evidence on the safety of expectant management of second-trimester miscarriage, medical or surgical management is preferred beyond 12-13 weeks gestational age.
Although there is a lack of consensus, complete abortion is often defined as the absence of a gestational sac on ultrasound with an endometrial stripe thickness of less than 30 mm. This ultrasound is usually performed 7-14 days after the initiation of medical management for spontaneous abortion. Patient-reported resolution of cramps and bleeding is also useful in confirming complete abortion. Beta-hCG levels do not need to be followed to 0, unless the location of the pregnancy within the pelvis remains unknown, or if persistent bleeding and constitutional symptoms of malignancy raise suspicion for the gestational trophoblastic disease. Regardless of the management approach, patients should be counseled on the level of bleeding that would warrant seeking care. This is often defined as the soaking of two menstrual pads per hour for two consecutive hours. Women who are Rh (D) negative and not yet sensitized to Rh (D) factor should be given Rh (D) immune-globulins within 72 hours of the onset of miscarriage. A dose of 50-120 mcg is recommended in the first trimester and 300 mcg in the second trimester.
Hormonal contraception may be initiated immediately after the resolution of early pregnancy loss, including the placement of an intrauterine device, which is only contraindicated in the setting of septic abortion . Attempting conception immediately is also safe, and couples who attempt conception within three months after miscarriage experience higher rates of successful pregnancy and live birth than those who postpone conception. However, the weeks to months after a miscarriage are often accompanied by feelings of grief or even guilt, anxiety, and depression for both the woman and her partner. Although there is limited evidence for the effectiveness of psychological counseling, patients and their families will likely experience better outcomes if these emotions and feelings are addressed early.
The differential diagnosis of spontaneous abortion can be constructed by considering the pelvic organs that could be responsible for vaginal bleeding early in pregnancy.
These differential diagnoses can usually be sufficiently evaluated through history, physical exam, and pelvic ultrasound.
Complications of spontaneous abortion include:
Expecting mothers should be counseled on the avoidance of the modifiable risk factors for miscarriage. However, there is limited evidence to support the use of any single prevention strategy. Pelvic rest, tocolytics, anticoagulants, and supplemental beta-hCG have not been shown to decrease the risk of early pregnancy loss. Aspirin has only been shown to reduce the rate of spontaneous abortion in women with anti-phospholipid antibody syndrome. Likewise, supplemental progesterone has only been shown to prevent early pregnancy loss in women with recurrent spontaneous abortion. Also, genetic testing for maternal and fetal chromosomal abnormalities or anti-phospholipid syndrome is only recommended in the setting of recurrent miscarriage.
Spontaneous abortion is a pregnancy loss before 20 weeks of gestational age.
Approximately half of the miscarriages are due to unknown genetic abnormalities.
Alcohol or drug use, infections, chronic disease, environmental exposures, and structural uterine abnormalities are other important risk factors.
Symptoms and signs of early pregnancy loss depend on the type.
Types include missed, threatened, inevitable, incomplete, complete, recurrent, and septic.
The evaluation usually involves a thorough history, physical exam, beta-HCG measurement, and pelvic ultrasound.
Although management also depends on the type, expectant, medical, and surgical approaches are generally equally effective.
Only aspirin in the setting of the anti-phospholipid syndrome and supplemental progesterone in the context of recurrent miscarriage have demonstrated the potential for prevention.
Testing for genetic abnormalities and anti-phospholipid syndrome should generally be reserved for cases of recurrent early pregnancy loss.
Since spontaneous abortion can occur across multiple settings, including home, clinic, and hospital, team-based care is essential. Emergency department providers must ensure the seamless transfer of medical records, including relevant labs and imaging, to outpatient clinics for appropriate follow-up. In the outpatient setting, convenient scheduling of frequent appointments is critical, as well as clear instructions for patients on when to present to the clinic versus emergency department for persistent symptoms. Finally, although the medical aspects of miscarriage management can be complicated, the psychological well being of the patient and her family cannot be neglected.
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