Early Pregnancy Loss
- Author: Elizabeth E Puscheck, MD; Chief Editor: Richard Scott Lucidi, MD more...
Background
An abortion is the spontaneous or induced loss of an early pregnancy. The period of pregnancy prior to fetal viability outside of the uterus is considered early pregnancy. Most consider early pregnancy to end at 20 weeks' gestation or when the fetus weighs 500 grams. The term miscarriage is used often in the lay language and refers to spontaneous abortion.
Pathophysiology
A spontaneous abortion is a process that can be divided into 4 stages—threatened, inevitable, incomplete, and complete. The 4 stages of abortion form a continuum. Most studies do not differentiate separately between the epidemiology and pathophysiology of each entity.
Threatened abortion
Threatened abortion consists of any vaginal bleeding during early pregnancy without cervical dilatation or change in cervical consistency. Usually, no significant pain exists, although mild cramps may occur. More severe cramps may lead to an inevitable abortion.
Threatened abortion is very common in the first trimester; about 25-30% of all pregnancies have some bleeding during the pregnancy. Less than one half proceed to a complete abortion. On examination, blood or brownish discharge may be present in the vagina. The cervix is not tender, and the cervical os is closed. No fetal tissue or membranes have passed. The ultrasound shows a continuing intrauterine pregnancy. If an ultrasound was not performed previously, it is required at this time to rule out an ectopic pregnancy, which could present similarly. If the uterine cavity is empty on ultrasound, obtaining a human chorionic gonadotropin (hCG) level is necessary to determine if the discriminatory zone has been passed.
The discriminatory zone is the level of hCG beyond which a normal, singleton, intrauterine pregnancy is consistently visible by ultrasound. The discriminatory zone may vary depending on a number of factors, including the hCG assay type and reference calibration standard used, ultrasound equipment resolution, the skill and experience of the sonographer, and patient factors (eg, obesity, leiomyomas, uterine axis, multiple gestations). Also, the discriminatory zone will vary depending on whether the ultrasound is performed abdominally or vaginally. Therefore, having a universal discriminatory zone is difficult, and it optimally should be calculated at each site.
Some studies recommend that a gestational sac should be visualized by 5.5 weeks' gestation; a gestational sac should be visualized with an hCG level of 1500-2400 mIU/mL for transvaginal ultrasound or with an hCG level over 3000 mIU/mL for a transabdominal ultrasound. If the hCG level is higher than the discriminatory zone and no gestational sac is visualized in the uterus, then consider that an ectopic pregnancy may be present.[1] Multiple gestations are an exception and can have higher hCG levels earlier in gestation because more hCG is being made by the trophoblasts from the multiple implantations. Thus, the gestational sac(s) may not be visible on ultrasound despite the hCG levels being higher than the discriminatory zone. Even with multiple gestations, the gestational sacs should be visible at a similar gestational age as singleton gestations or about 6 weeks' gestation if the dating is good.
A clinician should be concerned about ectopic pregnancy but cannot make the diagnosis of ectopic pregnancy just because the hCG level is higher than the discriminatory zone and the uterus appears empty on ultrasound. Many of these pregnancies are abnormal intrauterine pregnancies as opposed to ectopic. One needs to take into consideration the clinical history, and estimated gestational age by LMP or date of conception, if known. A positive pregnancy test result and an ultrasound that does not reveal the location is known as a pregnancy of unknown location (PUL).[2] Occasionally, a normal intrauterine pregnancy does result. Depending on the clinical scenario, a clinician may choose to observe this patient with serial hCG levels and ultrasonography instead of intervening, or a clinician may need to intervene depending on the situation.
Inevitable abortion
Inevitable abortion is an early pregnancy with vaginal bleeding and dilatation of the cervix. Typically, the vaginal bleeding is worse than with a threatened abortion, and more cramping is present. No tissue has passed yet. On ultrasound, the products of conception are located in the lower uterine segment or the cervical canal.
Incomplete abortion
Incomplete abortion is a pregnancy that is associated with vaginal bleeding, dilatation of the cervical canal, and passage of products of conception. Usually, the cramps are intense, and the vaginal bleeding is heavy. Patients may describe passage of tissue, or the examiner may observe evidence of tissue passage within the vagina. Ultrasound may show that some of the products of conception are still present in the uterus.
Complete abortion
Complete abortion is a completed miscarriage. Typically, a history of vaginal bleeding, abdominal pain, and passage of tissue exists. After the tissue passes, the patient notes that the pain subsides and the vaginal bleeding significantly diminishes. The examination reveals some blood in the vaginal vault; a closed cervical os; and no tenderness of the cervix, uterus, adnexa, or abdomen. The ultrasound demonstrates an empty uterus.
Missed abortion
A fifth term that does not follow the continuum but is important to be aware of is missed abortion. A missed abortion is a nonviable intrauterine pregnancy that has been retained within the uterus without spontaneous abortion. Typically, no symptoms exist besides amenorrhea, and the patient finds out that the pregnancy stopped developing earlier when a fetal heartbeat is not observed or heard at the appropriate time. An ultrasound usually confirms the diagnosis. No vaginal bleeding, abdominal pain, passage of tissue, or cervical changes are present.
Epidemiology
Frequency
United States
The overall miscarriage rate is reported as 15-20%, which means 15-20% of recognized pregnancies result in miscarriage. The frequency of spontaneous miscarriage increases further with maternal age. With the development of highly sensitive assays for hCG levels, pregnancies can be detected prior to the expected next period. When these highly sensitive hCG assays are used early, the magnitude of pregnancy loss significantly increases to about 60-70%. Late implantation by the conceptus beyond the usual 8-10 days after ovulation also has an increased risk of miscarriage.
About 80% of miscarriages occur within the first trimester. The frequency of miscarriage decreases with increasing gestational age. Recurrent early pregnancy loss, defined as 2-3 consecutive losses of clinical pregnancies, affects about 1% of all couples.
Risk factors
Independent risk factors for a spontaneous miscarriage include advanced age, extremes of age, feeling stressed, and advanced paternal age.[3, 4, 5] Symptoms of vaginal bleeding but not abdominal pain are associated with increased risk of miscarriage. One paper suggests that miscarriage can occur in about 50% of patients who present with threatened abortion.
International
No significant difference exists between international rates and the rates in the United States.
Mortality/Morbidity
A complete abortion is unlikely to cause any significant risk of mortality unless significant blood loss or infection occurs. Morbidity would be increased if anemia or infection develops. Patients who are pregnant may bleed quickly and significantly. Distinguishing the causes of bleeding during pregnancy is important.
Incomplete and inevitable abortions are a cause for concern when significant bleeding or infection occurs. If treatment is not performed in a timely manner, significant morbidity and mortality may occur. Retained products of conception may occur after a spontaneous abortion or after a suction D&C.
Patients with retained products usually return for medical care with symptoms of increased bleeding, increased cramping, and/or infection. Caring for these patients quickly with intravenous antibiotics is important, and, after the antibiotics are administered, then a suction D&C is performed. These patients are at risk for developing Asherman syndrome, which consists of adhesions within the uterine cavity. Patients who develop Asherman syndrome may present with amenorrhea or decreased menstrual flow. Asherman syndrome may compromise future fertility. When significant bleeding occurs, fluid management and transfusions may be required while stabilizing the patient prior to a suction D&C.
A complication of D&C is perforation of the uterus, which may be handled by observation. If the patient shows signs of uncontrolled bleeding, then proceeding to a laparoscopy or laparotomy to control the bleeding may be necessary. The choice for laparoscopy or laparotomy depends on the stability of the patient. Occasionally, the perforation is in the area of the uterine vessels or other area where the bleeding is difficult to control and a hysterectomy or uterine artery embolization may be necessary. When bleeding is severe, the patient can easily go into hypovolemic shock or disseminated intravascular coagulopathy (DIC). Both of these situations need prompt attention and treatment.
Surveillance data suggest that spontaneous miscarriages and induced abortions accounted for about 4% of pregnancy-related deaths in the United States.[6]
Race
Early pregnancy loss may occur in any race without distinction.
Sex
Early pregnancy loss only affects females.
Age
As women mature, the incidence of spontaneous miscarriages increases.
Typically, the distribution of miscarriage rates by age occurs as follows: younger than 35 years old, 15% miscarriage rate; 35-39 years old, 20-25% miscarriage rate; 40-42 years old, about 35% miscarriage rate; and older than 42 years old, about 50% miscarriage rate.
Women who conceive using donor eggs have miscarriage rates that are similar to the egg donor's age and not the recipient's age. This information is well documented on the CDC's Assisted Reproductive Technology Web site, and it indicates that miscarriages are increased significantly due to aging oocytes rather than due to the aging uterus.
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