Chapter 45: The Role of Sonography in Obstetrics

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1

abruptio placentae

bleeding from a normally situated placenta as a result of its complete or partial detachment after the 20th week of gestation

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amniocentesis

aspiration of a sample of amniotic fluid through the mother’s abdomen for diagnostic analysis of fetal genetics, maturity, and/or disease

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amnion

smooth membrane enclosing the fetus and amniotic fluid; it is loosely fused with the outer chorionic membrane except at the placental insertion of the umbilical cord, where the amnion is contiguous with the membranes surrounding the umbilical cord

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anencephaly

a neural tube defect where absence of the brain, including the cerebrum, the cerebellum, and basal ganglia, may be present

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aneuploidy

fetal syndromes associated with an abnormal number of chromosomes

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cerclage

the ligatures around the cervix uteri used to treat cervical incompetence during pregnancy

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cervix

inferior segment of the uterus, which is normally more than 3.5 cm long during pregnancy, decreasing in length during labor

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chorion

cellular, outermost extraembryonic membrane, composed of trophoblast lined with mesoderm; the outer chorion (villous chorion) develops villi, which are vascularized by allantoic vessels and give rise to the placenta; the inner chorion (the smooth chorion) is fused with the amnion except at the placental cord insertion

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corpus luteum

a functional structure within the normal ovary, which is formed from cells lining the graafian follicle after ovulation; the corpus luteum produces estrogen and progesterone and may become enlarged and appear cystic during early pregnancy

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ductus venosus

vascular structure within the fetal liver that connects the umbilical vein to the inferior vena cava and allows oxygenated blood to bypass the liver and return directly to the heart

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embryo

developing individual from implantation to the end of the 9th week of gestation

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embryonic age (conception age)

age of embryo stated as time from day of conception

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gestational (menstrual) age

length of pregnancy defined in the United States as number of weeks from first day of last normal menstrual period (LNMP)

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gestational sac

structure lined by the chorion that normally implants within the uterine decidua and contains the developing embryo

15

gravidity (G)

total number of pregnancies

16

hydatidiform mole

abnormal conception in which there is partial or complete conversion of the chorionic villi into grapelike vesicles

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incompetent cervix

a condition in which the cervix dilates silently during the second trimester; without intervention, the membranes bulge through the cervix and rupture, and the fetus drops out, resulting in a premature preterm delivery

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intrauterine growth restriction (IUGR)

reduced growth rate (symmetrical IUGR) or abnormal growth pattern (asymmetrical IUGR) of the fetus, resulting in a small for gestational age (SGA) infant

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lower uterine segment

thin expanded lower portion of the uterus that forms in the last trimester of pregnancy

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macrosomia

exceptionally large infant with excessive fat deposition in the subcutaneous tissue; most frequently seen in fetuses of diabetic mothers

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maternal serum alpha-fetoprotein (MSAFP)

one of several biochemical tests used to assess fetal risk for aneuploidy or fetal defect; a component of the “quad screen,” the normal value of MSAFP varies with gestational age; assessment of gestational age is essential for accurate interpretation of results

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nuchal translucency

a collection of fluid that extends behind the fetal neck and along the spine in the first trimester

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oligohydramnios

reduced amount of amniotic fluid

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parity (P)

number of live births

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placenta

organ of communication in which nutrition and products of metabolism are interchanged between the fetal and maternal blood systems; is formed from the chorion frondosum with a maternal decidual contribution

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placenta previa

placental implantation encroaches upon the lower uterine segment; if the placenta presents first in late pregnancy, bleeding is inevitable

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polyhydramnios

excessive amount of amniotic fluid

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quad screen

maternal serum biochemical levels in the second trimester of human chorionic gonadotropin (hCG), alpha-fetoprotein (AFP), estriol, and inhibin A

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trimester

a 40-week pregnancy is divided into three 13-week periods from the first day of the last normal menstrual period (weeks 1 through 13, first trimester; weeks 14 through 27, second trimester; week 28 to term, third trimester)

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umbilical cord

connecting lifeline between the fetus and placenta; it contains two umbilical arteries, which carry deoxygenated fetal blood, and one umbilical vein, which carries oxygenated fetal blood encased in Wharton’s jelly

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yolk sac

a circular structure within the gestational sac seen sonographically between 4 and 10 weeks’ gestational age; the yolk sac supplies nutrition, facilitates waste removal, and is the origin of early hematopoietic stem cells in the embryo; it lies between the chorion and the amnion

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zygote

products of conception from fertilization through implantation; the zygotic stage of pregnancy lasts for approximately 12 days after conception