Excerpt from First-Trimester Pregnancy Loss

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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 20-24 weeks' gestation. 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.

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 or miscarriage. On examination, blood or brownish discharge may exist 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 an intrauterine pregnancy is consistently visible. The discriminatory zone may vary depending on a number of factors, including 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.

However, some studies recommend that an estimate would be 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.

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 cramps are present. No tissue has passed yet.

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 describe passage of tissue, or the examiner observes evidence of tissue passage within the vagina. The ultrasound confirms that some of the products of conception are still present in the uterus.

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.

These 4 stages of abortion described above form a continuum. Most studies do not differentiate separately between the epidemiology and pathophysiology of each entity described above.

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 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.

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 an increasing gestational age. Recurrent miscarriage, defined as 2-3 pregnancy losses, affects about 1% of all couples.

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 an anemia or infection develops. Patients who are pregnant may bleed quickly and significantly. Distinguishing the causes of bleeding during pregnancy is important.

Threatened abortions usually bleed, a viable intrauterine pregnancy is visible on ultrasound, and the cervical canal is closed. A complete abortion will have a history of bleeding and significant cramping with passage of tissue, followed by a marked reduction in bleeding and resolution of cramping. With a complete abortion, the ultrasound demonstrates an empty uterus and the examination is notable for a closed cervical os. Incomplete or inevitable abortions have bleeding and an open cervical os on examination. The ultrasound may show clots or an intrauterine pregnancy.

These latter 2 conditions (incomplete and inevitable abortions) are a cause for concern when significant bleeding or infection occurs. If a suction dilatation and curettage (D&C) is not performed in a timely manner, significant morbidity and mortality may occur. Retained products of conception also 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 or a repeat suction D&C is performed. These patients will be 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 on ultrasound, then proceeding to a laparoscopy or laparotomy with cauterization of the bleeding area 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 may be necessary. When bleeding is out of control, the patient easily can go into hypovolemic shock or disseminated intravascular coagulopathy (DIC). Both of these situations need prompt attention and treatment.

Race

Complete abortions may occur in any race without distinction.

Sex

Complete abortions only affect females.

Age

Complete abortions only occur in reproductive-aged women unless in vitro fertilization was used with donor eggs in menopausal women. 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.

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