Role of Sonography in Obstetrics – Key Terms (First to Third Trimester)

A set of vocabulary-style flashcards covering key terms and concepts from the notes on first-trimester imaging and second/third-trimester obstetric sonography.

Transabdominal examination

Ultrasound assessment of the pelvis via the abdominal wall; provides an overview of the pelvic cavity and uterus, can image from cervix to fundus and assess ovaries and adnexal fluid or masses.

Transvaginal transducer

Ultrasound probe inserted vaginally, offering higher resolution with a more limited view, excellent visualization of embryo, yolk sac, amnion, chorion, and gestational sac.

Transperineal examination

Ultrasound approach through the perineum when additional views are needed or to assess specific structures.

Embryo

Early developmental stage of the developing human organism seen in the first weeks of gestation.

Fetus

Developing human after embryonic period; typically referenced in later first trimester onward in obstetric imaging.

Gestational sac

Fluid-filled cavity within the uterus that indicates pregnancy; its presence and location (intrauterine vs. extrauterine) are noted.

Intrauterine vs. extrauterine gestational sac

Intrauterine sac is located within the uterus; extrauterine sac indicates an ectopic pregnancy outside the uterus.

Yolk sac

Earliest structure seen within the gestational sac; its presence supports intrauterine pregnancy.

Embryo seen at ~4 weeks

Embryo appears as an echogenic curved structure adjacent to the yolk sac in early gestation.

Crown-rump length (CRL)

Most accurate first-trimester measure of gestational age; should be recorded when the embryo is present.

Gestational age

Estimated age of the pregnancy based on ultrasound measurements and development milestones.

hCG levels

Human chorionic gonadotropin; pregnancy hormone typically positive by 7–10 days embryonic age.

Placenta (trophoblastic reaction)

Thickened density along part of the gestational sac margin representing placental formation; a trophoblastic reaction may be seen.

Bowel herniation

Physiologic herniation of bowel into the umbilical cord or outside the abdomen at 8–11 weeks that later returns to the abdomen.

Cardiac activity

Presence of fetal cardiac motion; usually detectable when embryo is ~5 mm or larger in length.

Fetal heart rate (HR)

Pace of the fetal heart; varies with development (early around ~90 bpm, up to ~180 bpm, then ~120–160 bpm later in pregnancy).

Fetal number

Documentation of how many fetuses are present; used to assess multiple gestations and document amniotic and chorionic membranes (chorionicity and amnionicity).

Amnionicity and chorionicity

Membrane structures documenting whether fetuses share the same amniotic sac or chorion (important in multiples).

Corpus luteum

Structure in the ovary that may be present in early pregnancy and supports the pregnancy until placentation.

Uterine texture

Texture of the uterus on ultrasound; inhomogeneous texture may indicate leiomyomatous growth or other pathology.

Leiomyomatous growth

Fibroids within the uterus that may affect pregnancy management and imaging.

Placenta previa

Placental location low in the uterus near or over the internal cervical os, potentially impacting delivery.

Hydatidiform mole

Abnormal pregnancy with trophoblastic tissue proliferation; a pathological cause of placental abnormality.

Cervical cerclage

Surgical procedure to reinforce a weak cervix in certain pregnancies to prevent preterm birth.

Ectopic pregnancy

Pregnancy implanted outside the uterine cavity, most commonly in the fallopian tube.

Fetal well-being

Assessment of fetal health and status during ultrasound, including growth and organ function indicators.

Amniotic fluid abnormalities

Deviations from normal amniotic fluid volume, including too much (hydramnios/polyhydramnios) or too little (oligohydramnios).

Amniotic fluid index (AFI)

A semiquantitative method to estimate amniotic fluid volume (e.g., four-quadrant AFI or single deepest pocket).

Hydramnios (polyhydramnios)

Excessive amniotic fluid volume.

Oligohydramnios

Too little amniotic fluid volume.

Placental location

Position of the placenta within the uterus; important to rule out placenta previa by ensuring placental edge is away from the cervical os.

External cephalic version (ECV)

Procedure to attempt turning a fetus from breech to cephalic presentation near term.

Premature rupture of membranes (PROM)

Rupture of the amniotic sac before labor begins.

Premature labor

Onset of labor before 37 weeks of gestation.

Biometric parameters

Sonographic fetal measurements used to estimate growth and gestational age: BPD, HC, FL, and AC.

Biparietal diameter (BPD)

Measurement of the width of the fetal head; performed in the axial plane including the thalamus and cavum septi pellucidi.

Head circumference (HC)

Measurement around the largest circumference of the fetal head; less affected by head shape than BPD.

Brachycephaly/Dolichocephaly

Head shape variations; brachycephaly is a rounder head, dolichocephaly a longer, narrower head.

Femur length (FL)

Measurement of the femur bone length; reliable after ~14 weeks and best when the femoral shaft is perpendicular to the beam.

Abdominal circumference (AC)

Measurement around the fetal abdomen at the level of the portal vein and umbilical vein; used to estimate fetal weight.

Fetal weight estimation

Estimating fetal weight using biometric measurements; accuracy varies and significant errors can occur.

Umbilical cord vessels

Typically two arteries and one vein; imaging may count vessels when possible.

Umbilical cord insertion

Site where the cord attaches to the fetus's abdomen; an important anatomical landmark.

Anatomy documentation (second/third trimester)

Systematic recording of fetal head, neck, chest, abdomen, spine, extremities, and gender when indicated.

Four-chamber view

A standard view of the fetal heart showing both atria and both ventricles, used to assess cardiac structure.

Outflow tracts

Fetal heart views including the right and left ventricular outflow tracts to assess major vessels.

Stomach situs

Position and appearance of the stomach; part of fetal abdominal assessment.

Kidneys and bladder

Assessment of renal structure and urinary bladder in the fetus.

Umbilical cord insertion and vessels

Evaluation of where the cord inserts into the abdomen and the number of vessels.

Gender determination

Determination of fetal sex when visually or clinically indicated; more common in later gestation or targeted studies.

Fetal anatomy after 18 weeks

Comprehensive evaluation of fetal structures may be feasible and documented after 18 weeks when image quality allows.

Head and neck structures (protocol)

Includes cerebellum, choroid plexus, cisterna magna, lateral ventricles, falx, Cavum septi pellucidi, and upper lip.

Chest structures (protocol)

Includes four-chamber view of the heart and, if possible, outflow tracts for extended cardiac assessment.

Abdomen structures (protocol)

Stomach, kidneys, bladder, umbilical cord insertion, and vessels within the abdomen.

Spine and extremities (protocol)

Imaging of cervical-to-sacral spine and presence/absence of limbs.

Gender documentation (protocol)

Recording fetal sex when medically indicated, particularly in low-risk pregnancies for multiple gestations.

Diagnostic vs screening

Diagnostic tests provide definite information about a finding; screening indicates risk but is not definitive.

Sensitivity and limitations

Accuracy of ultrasound varies by factors like maternal habitus, operator skill, risk level, and fetal anomaly type; there are limits and false positives may occur.