Understand the clinical utility of human chorionic gonadotropin (hCG) results in pregnancy, normal and ectopic, spontaneous abortion (miscarriage), and gestational trophoblastic disease.
Learn how to diagnose common complications of pregnancy, notably preeclampsia, eclampsia, HELLP syndrome, and fatty liver associated with pregnancy.
Understand the causes and the diagnosis of female infertility.
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.
Normal pregnancy lasts approximately 40 weeks, as dated from the first day of the previous menstrual period, and is typically divided into three 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.
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).
TABLE 20–1Routine Testing in Normal Pregnancy ||Download (.pdf) TABLE 20–1 Routine Testing in Normal Pregnancy
|Test ||Comments |
|hCG ||Should double every 1.5–2 days for the first 8 weeks |
|First-trimester screen (free beta hCG, PAPP-A) ||To screen for trisomy 21 |
|Second-trimester “quad” screen ...|