Chapter 20: Female Genital System

Clinical laboratory testing is useful for the diagnosis and management of pregnancy and infertility, and such testing is reviewed in this chapter. Gestational diabetes mellitus (GDM) is discussed in Chapter 17, and hemolytic disease of the newborn (HDN) is found in Chapters 7 and 12. Female physiology and biochemistry including amenorrhea are discussed in Chapter 22. The female genital tract is also a common site for infections, which may be sexually transmitted, and it is a common site for tumors. The infections are presented in Chapter 5, and tumor descriptions are found in textbooks of anatomic pathology.

Description

Normal pregnancy lasts approximately 40 weeks, as dated from the first day of the previous menstrual period, and is typically divided into 3 intervals or trimesters each lasting approximately 13 weeks. Approximately 5 days after fertilization, a blastocyst implants in the uterus. Trophoblast cells of the blastocyst invade the endometrium with chorionic villi leading to a placenta and the forming embryo surrounded by amniotic fluid. The placenta nourishes the embryo and produces hormones vital to pregnancy such as human chorionic gonadotropin (hCG), progesterone, estradiol, estriol, and estrone. The amniotic fluid protects the embryo and changes composition as the pregnancy progresses. The embryo undergoes rapid cell division, differentiation, and growth in the first trimester (0-13 weeks). By 10 weeks, most major structures are formed resulting in a fetus. The second trimester (13-26 weeks) is associated with rapid fetal growth. Completion of maturation occurs in the third trimester (26-40 weeks) resulting in a term pregnancy between 37 and 42 weeks.

Diagnosis

Once pregnancy has been achieved, several laboratory tests are routinely performed to help ensure an optimal maternal and fetal outcome (Table 20–1). Most testing in pregnancy is performed on maternal serum because it is easy to obtain and provides minimal risk to the pregnancy, but maternal urine and amniotic fluid specimens may also be necessary. Of note, pregnancy has an effect on many laboratory tests, other than those used to diagnose and manage pregnancy, and these alterations should be considered when interpreting laboratory tests from pregnant women (Table 20–2).

hCG is one of the most commonly ordered tests in pregnancy. It is heterodimer composed of 2 nonidentical nonconvalently bound glycoprotein subunits, alpha and beta, that is synthesized by the trophoblasts of the placenta. Only the intact molecule is biologically active. A single gene for the alpha subunit of all 4 glycoprotein hormones (thyroid-stimulating hormone [TSH], luteinizing hormone [LH], follicle-stimulating hormone [FSH], and hCG) is found on chromosome 6. hCG stimulates the LH receptor on the corpus luteum to produce progesterone that helps to prevent pregnancy loss.

Detectable amounts of hCG (>2-5 IU/L, depending on the assay) are present in serum 8 to 11 days after conception. Qualitative urine hCG tests are usually sufficient for screening, but the detection limits of qualitative tests range from 20 to 50 IU/L, limiting their use to the time following a missed menstrual period or greater than 14 days after conception. As opposed to qualitative testing, quantitative testing offers sensitivity as low as 2 to 5 IU/L and serial measurements may be helpful to reveal problems in a pregnancy. In normal pregnancies, hCG doubles every 1.5 to 2 days for the first 8 weeks (Table 20–1) and peaks around 100,000 to 500,000 IU/L.

Blood and urine contain many hCG variants, including free subunits, and hyperglycosylated and nicked forms. After 5 weeks of gestation the predominant hCG form in urine is the hCG beta core fragment. In addition, the hCG glycosylation changes as the pregnancy progresses. Quantitative hCG immunoassays typically measure total hCG beta concentrations using 2 antibodies against different regions of the beta subunit. False-negative hCG results can be seen in early pregnancy or when hCG concentrations are very high, causing a hook effect. False-positive results can be caused by heterophilic antibodies and by advanced maternal age (from pituitary hCG).

Other additional routine testing in pregnancy is performed to screen for common and/or treatable pregnancy complications such as gestational diabetes (see Chapter 17), hemolytic disease of the newborn (see Chapters 7 and 12), and infection (see Chapter 5) (Table 20–1).

Description

Maternal serum screening can be performed to identify individuals who need further diagnostic evaluation for fetal anomalies such as neural tube defects (NTDs), trisomy 21/Down syndrome, and trisomy 18. NTDs result from failure of fusion of the neural plate and failure of complete covering by the 27th day post conception. The extent and location of neural tissue exposed indicates the severity of the defect (ie, anencephaly, meningomyelocele, and encephalocele). The result of a NTD is a direct communication of the amniotic fluid with fetal plasma proteins, and release of alpha-fetoprotein (AFP) into amniotic fluid and maternal serum. Rates of NTDs have decreased due to the addition of folic acid to grain, as well as initiation of recommendations for folic acid supplementation prior to conception. Trisomy 21 or Down syndrome is caused by an extra copy of chromosome 21 and is the most frequent chromosomal disorder among live-born children (1/600 to 1/800 live births). Risk factors for Down syndrome include advanced maternal age, the birth of a previously affected child, and balanced parental structural rearrangement of chromosome 21. Affected children suffer from mental retardation, hypotonia, congenital heart defects, and a flat facial profile. The main phenotypic features of trisomy 18 include hypertonia, prominent occiput, small mouth, micrognathia, short sternum, and horseshoe kidney.

Screening

An additional discussion of maternal screening for Down syndrome is found in Chapter 7.

Screening for NTDs is done at 15 to 22 weeks gestation by measurement of serum AFP that is expressed as a multiple of the median population (MoM). MoMs greater than 2 or 2.5 are considered abnormal and should be followed up by high-resolution ultrasound or measurement of amniotic fluid AFP and acetylcholinesterase.

Sequential serum screening is performed to screen for trisomies and combines first- and second-trimester testing. First-trimester testing is performed between 10 and 14 weeks and includes measurement of hCG and pregnancy-associated plasma protein-A (PAPP-A) as well as an ultrasound measurement for infant nuchal translucency (NT). Specific training is required of operators for determination of NT. This procedure is highly operator dependent. Free beta hCG testing is more accurate than intact hCG testing in the first trimester and is used instead of intact hCG for the first-trimester screen. PAPA-A is a protein produced by the placenta. Elevated hCG, decreased PAPP-A, and increased NT are seen in pregnancies affected by trisomy 21.

In the sequential screen, first-trimester screening is followed up with second-trimester screening at 15 to 22 weeks, with measurement of serum AFP, hCG, estriol, and inhibin A (ie, the quad screen). AFP is the most abundant serum protein in the fetal circulation. Maternal serum AFP is detectable at 10 weeks and peaks at 15 to 20 weeks. Estriol is the predominant estrogen of pregnancy and also the most difficult to measure because of low concentration and limited stability. Inhibin A, secreted by the ovaries and placenta, is a glycoprotein that inhibits FSH. Concentrations of individual analytes from the first- and second-trimester screens and NT measurements are combined into a risk assessment algorithm that adjusts for gestational age, maternal weight, number of fetuses, and presence or absence of diabetes mellitus. The most frequent causes of abnormal results include incorrect dating, the presence of twins, and fetal demise. For this reason, an ultrasound confirming gestational age is the first line of testing in a patient with apparently increased risk. Fetal karyotyping is necessary to confirm chromosomal abnormalities.

Second trimester-only testing can be done and should utilize the quad screen. Elevated hCG, increased inhibin A, decreased estriol, and decreased AFP are seen in pregnancies affected by trisomy 21, while all 4 analytes in the quad screen are decreased in pregnancies affected by trisomy 18. Patients at risk should undergo further diagnostic evaluation as described with sequential screen.

Recently, new methods have been developed for trisomy 21 screening using circulating fetal DNA. These methods utilize “massively parallel genomic sequencing” (MPGS). DNA fragments are isolated from a sample of maternal blood, which contains a mixture of maternal DNA and infant DNA. The DNA fragments are amplified and then sequenced. The number of sequences that originate from a particular chromosome is counted and tabulated for each chromosome. If a fetus has an extra chromosome, then the percentage of DNA fragments from that chromosome is higher than expected. These tests have been shown to have excellent detection rates (~99%) with very low false-positive rates (~0.2%). Currently, MPGS is only validated for the detection of Down syndrome and not other fetal aneuploidies such as trisomy 18 or trisomy 13. The test does have the capability of detecting these disorders and, if they are detected, the results are reported. However, because the test has not been thoroughly investigated for detecting trisomy 18 or trisomy 13, a negative result does not rule out their presence. Also, the test does not detect open NTDs (eg, spina bifida), for which screening usually involves biochemical (not genetic) screening tests.

The American College of Obstetricians and Gynecologists (ACOG) cautions that these tests are screening tests, not diagnostic tests. They also recommend that DNA-based screening tests be performed only on women who are at increased risk of having a fetus with aneuploidy, including women with: maternal age 35 years or older at delivery, fetal ultrasound findings suggesting aneuploidy, a previous aneuploid pregnancy, or abnormal biochemical screening test results.

Description

Ectopic pregnancies arise if the fertilized egg implants in a location other than the body of the uterus, primarily in the fallopian tube. Of all reported pregnancies, 1.3% to 2% are extrauterine. The nonuterine location of implantation prevents normal development. Despite increased awareness and improved diagnostic modalities, such as serial hCG and transvaginal ultrasound, ectopic pregnancies are the leading cause of maternal death in the first trimester. Risk factors for ectopic pregnancy include tubal damage from either infection or disease, smoking, infertility, and previous miscarriage.

Diagnosis

Three classic symptoms of an ectopic pregnancy include lower abdominal pain, vaginal bleeding, and an adnexal mass. However, only 25% of women with ectopic pregnancy have these symptoms at the time of presentation, making laboratory testing and transvaginal ultrasound examination essential for diagnosis and management. In ectopic pregnancies, abnormal concentrations of hCG are present (Table 20–3). hCG concentrations in ectopic pregnancy range from undetectable to 200,000 IU/L, depending on the size and viability of the trophoblastic tissue. Therefore, the absolute concentration of hCG is not very useful in the diagnosis of ectopic pregnancy. Many utilize a so-called discriminatory zone of hCG in which a fetus should be visible when hCG concentrations are >2000 IU/L. However, recent studies suggest that the discriminatory zone is not very reliable and can lead to misdiagnosis. Instead serial testing reveals rates of hCG increase as slow as 35% over 2 days in ectopic pregnancy. Medical therapy with methotrexate or surgery is required to prevent rupture and significant hemorrhage.

Description

Spontaneous abortion or miscarriage refers to a pregnancy that ends spontaneously before the fetus has reached a viable gestational age. The most common complication of early pregnancy is spontaneous abortion, and it occurs in approximately 10% to 20% of all recognized pregnancies under 20 weeks gestation. The percentage increases if unrecognized or subclinical pregnancies are included. Risk factors include advanced maternal age, previous miscarriage, smoking, and alcohol or drug consumption. Chromosomal abnormalities account for approximately 50% of all miscarriages.

Recurrent spontaneous abortion is defined as 3 or more consecutive intrauterine pregnancy losses prior to 20 to 24 weeks of gestation. It affects up to 1% to 5% of fertile couples. Primary aborters have had no live births, while secondary aborters were able to achieve at least 1 successful pregnancy. Assisted reproduction technologies are much less effective in women with recurrent fetal losses compared with those with infertility.

Diagnosis

Women experiencing a miscarriage may present with a history of amenorrhea, vaginal bleeding, and lower abdominal pain. Serial measurements of hCG concentration in conjunction with physical examination and ultrasonography can be helpful in the diagnosis of spontaneous abortion. Decreasing hCG concentrations are consistent with a spontaneous abortion or nonviable pregnancy. Patients with a confirmed miscarriage can be managed expectantly, medically with misoprostol, or surgically. Following treatment, hCG concentrations can be monitored until the concentration is undetectable to confirm complete expulsion of products of conception. It may take 30 to 60 days before serum hCG concentrations are undetectable. The etiology of recurrent loss is often unclear, but can include genetic, anatomic, hormonal, thrombotic, placental, infectious, environmental, or psychological causes. Immunological factors may also play a role. Following a detailed history, physical examination, and radiological studies, additional laboratory tests may be helpful in determining the cause of the recurrent loss (Table 20–4). Of all the etiologic factors, only parental genetics has been shown to be a definitive cause of recurrent loss. Although uterine abnormalities, antiphospholipid antibodies, the Factor V Leiden mutation, and other thrombotic risk factors (see Chapter 11) are definitely associated with recurrent loss, there is not sufficient proof of a causative role.

Description

Gestational trophoblastic diseases are a spectrum of disease processes originating from the placenta that include hydatidiform mole, invasive mole, and choriocarcinoma. Malignant gestational trophoblastic diseases have the potential for local invasion and metastasis.

Hydatidiform moles are the most common and occur in 1 of 600 therapeutic abortions and 1 of 1100 pregnancies. Approximately 20% of patients will be treated for malignant sequelae after evacuation of a hydatidiform mole. Gestational choriocarcinoma occurs in approximately 1 in 30,000 pregnancies.

Diagnosis

Gestational trophoblastic diseases are usually diagnosed early in pregnancy. Patients present with abnormal bleeding and vague complaints. Ultrasound and serum hCG testing are used to make the diagnosis of gestational trophoblastic diseases. Ultrasound findings include the absence of a fetal heartbeat. hCG testing reveals greatly elevated hCG concentrations (Table 20–3). Dilation and evacuation (D&E) procedures are performed to treat patients. Serial hCG measurements should be performed after treatment to ensure complete removal of tumor and monitoring of disease for recurrence. Chemotherapy may be necessary in cases of malignant transformation.

Description

Preeclampsia is a multisystem disorder of unknown etiology, and it is a major cause of morbidity and mortality in pregnancy. Patients develop elevated blood pressure and proteinuria. In addition, coagulopathies, impaired liver function, renal failure, and cerebral ischemia may occur. Preeclampsia occurs in 2% to 8% of pregnancies. Eclampsia, in which women with preeclampsia have accompanying seizures, occurs less frequently. Eclampsia is more serious and carries a higher morbidity and mortality rate. Treatment includes controlling symptoms until delivery.

Diagnosis

Preeclampsia is diagnosed by the occurrence of new hypertension and proteinuria in the second half of pregnancy. Hypertension in pregnancy is defined as a persistent systolic blood pressure ≥140 mm Hg and/or a diastolic blood pressure ≥90 mm Hg. Proteinuria in preeclampsia is >300 mg/L protein in a 24-hour urine specimen or >1 g/L protein in a single urine specimen (Table 20–3). It should be demonstrated that seizures associated with eclampsia are not explained by a neurological disorder such as epilepsy.

Description

The HELLP syndrome involves hemolysis, elevated liver enzymes, and a low platelet count. The syndrome can occur during pregnancy, typically between weeks 27 and 36, or in association with preeclampsia; it can also occur postpartum.

Diagnosis

The HELLP syndrome and preeclampsia have similar clinical presentations. A low platelet count and abnormal liver enzymes are important to make a diagnosis of the HELLP syndrome (Table 20–3). The hemolysis in the HELLP syndrome is microangiopathic, and this results in schistocytes on the peripheral blood smear, an elevated indirect bilirubin, and an increased lactate dehydrogenase (LD) activity.

Description

Approximately 1 in 13,000 pregnancies is affected by fatty liver of pregnancy. First pregnancies and multiple gestation pregnancies are at a higher risk. Symptoms, which are nonspecific and include nausea and vomiting, right upper quadrant pain, and lethargy, typically begin around the 36th week of gestation. Liver biopsies show accumulation of microvesicular fat, which may be caused by a defect in mitochondrial beta oxidation of fatty acids or a long-chain 3-hydroxyacyl CoA dehydrogenase deficiency. Treatment involves immediate delivery to prevent fulminant hepatic failure requiring liver transplantation. Recurrence in subsequent pregnancies is rare.

Diagnosis

The diagnosis is made using both clinical symptoms and laboratory results. Although liver biopsy is virtually diagnostic in the setting of pregnancy, it is rarely necessary. The laboratory test abnormalities include mild elevations in liver enzymes (AST > ALT), increased bilirubin, hypoglycemia, and hyperuricemia (Table 20–3). Abnormal coagulation test results, as indicated by a prolonged prothrombin time, a prolonged partial thromboplastin time, and a low fibrinogen, are found in acute fatty liver of pregnancy, but not in HELLP syndrome, and this helps differentiate the 2 conditions.

Description

Infertility is defined as the inability to achieve a successful pregnancy following 1 year of unprotected intercourse. It is estimated that 15% to 25% of couples will experience an episode of infertility. Couples with primary infertility have had no previous successful pregnancies. Couples with secondary infertility had prior pregnancies, but are currently unable to conceive. Both primary and secondary infertility have common causes, most often problems with the hypothalamic–pituitary–gonadal axis.

Diagnosis

Factors contributing to female infertility include ovarian, hormonal, tubal, cervical, uterine, psychosocial, iatrogenic, and immunological factors. Ovulatory disorders, such as hypergonadotropic hypogonadism and hypogonadotropic hypogonadism, are the most common and are described in more detail in Chapter 22. Other disorders such as polycystic ovarian disease, obesity, thyroid dysfunction, androgen excess, and liver dysfunction can also contribute. Following a detailed history and physical examination, laboratory evaluation of female infertility is performed. Midluteal progesterone concentrations greater than 10 ng/mL indicate normal ovulation while concentrations less than 10 ng/mL suggest anovulation, inadequate luteal phase progesterone production, or inappropriate timing of sample collection. Serum concentrations of FSH and estradiol can be measured on day 3 of the menstrual cycle to indicate ovarian reserve. TSH and prolactin (PRL) can be used to assess for thyroid or pituitary dysfunction.