Spontaneous abortion or miscarriage is defined as the loss of pregnancy less than 20 weeks gestation. The American College of Obstetricians and Gynecologists (ACOG) estimates it is the most common form of pregnancy loss. It is estimated that as many as 26% of all pregnancies end in miscarriage and up to 10% of clinically recognized pregnancies.  Moreover, 80% of early pregnancy loss occurs in the first trimester.  The risk of miscarriage decreases after 12 weeks gestation.
The term miscarriage and abortion are used interchangeably. The term abortion refers to a termination of a pregnancy either natural or induced. There are several terms that describe different states of pregnancy loss. These terms include threatened, inevitable, complete and missed abortion. Threatened abortion is the presence of vaginal bleeding in early pregnancy but on pelvic exam, the cervical os is closed and the transvaginal ultrasound shows a viable fetus.  An inevitable abortion is when there is vaginal bleeding but on the pelvic exam, the cervical os is open meaning that the fetus or products of conception are expected to pass through the cervix in the near future. On transvaginal ultrasound, there can be either be a viable fetus or not.  A complete abortion is when there is initially vaginal bleeding and passing of products of conception through the cervix. On transvaginal ultrasound, there would be no remaining products of conception in the uterus. A missed abortion refers to when there was vaginal bleeding and perhaps some passage of tissue or products of conception. On pelvic exam, the cervical os would be closed. On transvaginal ultrasound, there would be retained products of conception and there would not be a viable fetus.
The most common cause of spontaneous pregnancy loss in the first trimester is chromosomal abnormalities. In most cases, it is too early to determine the exact cause of the abnormality. Risk of early pregnancy loss decreases with increasing gestational age and is relatively low after 15-weeks gestation in a genetically normal fetus.
Risk of miscarriage is multivariate, and while some maternal risk factors tend to be more important than others, there is no one predictor of future pregnancy loss. Maternal age is an important predictor in the risk of miscarriage. In women ages, 20 to 30 risk of miscarriage less than 20 weeks gestation is 8.9%. This increases to 74.7% for women over 40 years Another important predictor in the risk of early pregnancy loss is prior obstetrical history. The risk of miscarriage in a future pregnancy is approximately 20% after 1 miscarriage, 28% after 2 consecutive miscarriages, and 43% after 3 or more consecutive miscarriages.
Maternal comorbidities such as thrombophilia, antiphospholipid antibody syndrome, extremes of maternal weight and hypertension also increase the risk of miscarriage. Additional maternal risk factors have been identified such as cigarette smoking, large amounts of caffeine use, trauma and malnutrition. 
Signs of early pregnancy loss vary and can often be confused with complications or symptoms of a normal intrauterine pregnancy as well as ectopic pregnancy. Most commonly patients present with pelvic and abdominal cramping with or without vaginal bleeding and a positive pregnancy test or missed or abnormal menstrual cycle.
The most important determination when evaluating a pregnant patient with symptoms of miscarriage is whether or not this is a true loss, an ectopic pregnancy, molar pregnancy, or a viable pregnancy with complications.
Ultrasound is the gold standard for examining intrauterine contents and viability. This paired with a quantitative human chorionic gonadotropin (hCG) hormone level can help determine viability. hCG levels should double in 48 hours on serial exams.
At hCG levels between 1000 to 2000, it has been determined that transvaginal ultrasound (TVUS) is the most sensitive study for identifying intrauterine contents such as a gestational sac with or without a fetus or embryo. There have been multiple studies that reveal a correlation between hCG levels and stage of embryonic development seen on ultrasound. For instance, at a range of serum hCG between 800 to 1500 UI/I, a 1 to 3 mm gestational sac should be visible on TVUS. Furthermore, a yolk sac should be detectable within the range hCG level of 4500 to 7500 UI/I; with fetal heart motion visible at a range 8650 to 12,200 U/I.
Cardiac activity should be identifiable at a crown-rump length of 5 mm or greater.
Findings suggestive of but not definitive of early pregnancy loss on transvaginal ultrasound are a crown-rump length (CRL) of 7 mm or greater without fetal cardiac activity or an empty gestational sac with no embryo of 16 to 24 mm or greater in diameter. 
The American College of Obstetricians and Gynecologists (ACOG), therefore, recommends serial hCG levels as well as serial ultrasounds to determine viability.
Treatment options include expectant management, medication, or surgical interventions.
Decisions are often made jointly with the patient and the obstetrician as to which path to choose. As long as patients are hemodynamically stable and do not require emergency surgery, there is no difference in long-term outcomes when comparing these treatment options.
Expectant management is typically limited to those miscarrying in the first trimester due to lack of studies beyond that timeframe and presumed increased risk of bleeding complications beyond that. Approximately 80% of women achieve complete passage of intrauterine contents within 8 weeks.
Medical management can be used in the absence of contraindications including severe anemia, bleeding disorders or infection. Misoprostol, a prostaglandin analog, is given in 1 or 2 doses to achieve induced passage of intrauterine contents. Misoprostol can be taken in the oral form, sublingual, or as a vaginal suppository. Most women will achieve complete expulsion within 3 days, and very few need subsequent uterine curettage.
Surgical evacuation is another option in the treatment of early pregnancy loss and is achieved either with sharp curettage or suction curettage. Surgical evacuation is preferred in women who present with hemorrhage, hemodynamic instability, or signs of infection because these conditions require urgent treatment. This is also the preferred method of treatment for women with comorbid conditions such as cardiovascular disease, infection, severe anemia, or bleeding disorders.
While success rates for surgical evacuation reach 99%, the risk of complications among all 3 treatment options remains low and is equivocal in women without comorbid conditions or contraindications to one form or another. Hemorrhage and infection appear to be the 2 most common complications across all three treatment types.
Another important consideration that must be taken into account when evaluating pregnant females with complaints consistent with miscarriage is their Rh status. This is important due to the fact that the fetus could differ in Rh type from the mother. If mother and fetus have different Rh types, this sets up a scenario where the mother could be exposed to a differing Rh from exposure to the fetal blood type. This could cause the mother to produce antibodies against the different Rh to which it was exposed. These antibodies can then cross the placenta and affect the fetus. This can then present serious consequences to the fetus and cause the fetus to develop a high output cardiac failure state known as hydrops fetalis which is nearly 100% fatal. All women who have a blood type that is Rh(D) negative who are diagnosed with early pregnancy loss, and have not been sensitized, should receive Rh(D)-immune globulin 50 micrograms (or 300 micrograms if available) to prevent alloimmunization. Rh(D)-immune globulin should be administered as early as possible, within 72 hours, of diagnosis of miscarriage and immediately following surgical intervention.
To date, there exists no proven strategy to prevent early pregnancy loss. Suggestions such as pelvic rest and hormone administration have not been proven. However, some physicians advocate progestin administration early to women who have experienced multiple prior miscarriages. Anticoagulants or aspirin administration has only been proven to be beneficial in women with antiphospholipid antibody syndrome.
The differential for early pregnancy loss includes ectopic pregnancy, viable pregnancy with implantation bleeding, molar pregnancy, viable pregnancy with complications. There are also non-uterine causes of bleeding that can be mistaken for miscarriage such as vaginal trauma.
Patient education is important in early pregnancy loss as this can be an emotionally difficult diagnosis. Patient education should focus on maternal health and preparing for future pregnancy. There has been no data to support delaying conception after an early pregnancy loss to prevent subsequent miscarriage or complications. Although most physicians recommend abstaining from vaginal intercourse for 1 to 2 weeks after the passage of tissues, there is no data to support this recommendation.
Patients should also be provided with education regarding contraception after a miscarriage including the use of an intrauterine device or hormonal contraception as both have been deemed safe for use immediately following an early pregnancy loss.
It is important to provide each Rh(D) negative patient education on alloimmunization and risk of future pregnancy with regards to receiving Rh(D) immune globulin.
Most importantly, while there are no proven strategies to reduce the risk of subsequent pregnancy loss after a miscarriage, patient education on maternal health is important. Patients should be provided with education on managing blood pressure, extremes of weight and cigarette smoking cessation.
Miscarriage is the loss of a pregnancy before 20 weeks gestation.
Before 12 weeks, gestation most pregnancy loss is due to chromosomal abnormalities.
Maternal health such as high blood pressure, obesity and cigarette smoking may increase the risk of miscarriage.
Advanced maternal age has been proven to increase the risk of miscarriage with risks as high as 74% for women over age 40.
It is important to evaluate using transvaginal ultrasound to determine whether or not a pregnancy is viable.
For women with no co-morbid conditions, all 3 treatment options (medical, surgical or expectant management) have been proven equally safe and effective.
Treating patients who experience pregnancy loss requires close coordination between all members of the care team. Follow up care with an obstetrician needs to be coordinated. Clear and concise discharge instructions need to be given to the patient. This experience for the patient can be very emotionally taxing and needs to be handled with extreme compassion and sensitivity.
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