Ultrasound In Obstetrics

Question 1

What does an ultrasound do

Answer 1

Characterizes pregnancy location, identifies the number of embryos present, and aids in the prenatal diagnosis of fetal anomalies.

Question 2

Indications for USS in the first trimester

Answer 2

• to confirm a viable intrauterine pregnancy either trans-abdominally or trans-vaginally, ideally performed before 13 weeks and 6 days of gestation.
• to diagnose an “early pregnancy loss” which is defined by American College of Obstetricians and Gynecologists as a nonviable, intrauterine pregnancy with either an empty gestational sac, or a gestational sac containing an embryo or fetus without cardiac activity within the first 12 6/7 weeks of gestation.
• to provide an accurate gestational age assessment (Mean sac diameter (mm) + 30 = gestational age in days) or CRL (mm) + 42 days (+/- 3 days) = gestational age (days)
• In the setting of multifetal gestations, amnionicity and chorionicity should be documented.
• In the setting of desired genetic testing, nuchal translucency measurement aids in the screening assessment for fetal aneuploidy in conjunction with biomarkers.
• A first trimester ultrasound is also useful for the evaluation of maternal anatomy including assessment of the uterus, cervix and adnexal structures. The presence of adnexal masses, ovarian cysts, and/or leiomyomas should be documented and followed throughout pregnancy.

Question 3

Diagnostic findings of early pregnancy loss

Answer 3

1. ) Crown-rump length of 7 mm or greater and no heartbeat,
2. ) Mean sac diameter of 25 mm or greater and no embryo,
3. ) the absence of cardiac activity in an embryo 2 weeks or more after a scan that showed a gestational sac without a yolk sac, and/or
4. ) the absence of cardiac activity in an embryo 11 days or more after a scan that showed a gestational sac with a yolk sac.

Question 4

Indication of USS in the 2nd and 3rd trimester

Answer 4

• use fetal biometry to assess fetal growth: the fetus’ biparietal diameter, head circumferences, abdominal circumference or average abdominal diameter and femoral diaphysis length.

N.B: In the third trimester, the femur length is the best single biometric measurement of gestational age

• also can provide detailed information on fetal anatomy.

The basic fetal anatomic examination includes assessment of the following structures: lateral cerebral ventricles, choroid plexus, midline falx, cavum septi pellucidi, cerebellum, cistern magna, upper lip, four-chamber view of heart as well as left and right ventricular outflow tracts, size and location of stomach, urinary bladder and ureters, spinal anatomy, extremities, and gender. A more detailed anatomic survey may be indicated depending on the risk and concern for aneuploidy. The placenta should also be further characterized at this time, specifically noting its location and proximity to the internal cervical os as well as the number of vessels and insertion site of the umbilical cord

• an evaluation of fetal presentation(s), amniotic fluid volume, cardiac activity, and placentation.
• to diagnose or to monitor maternal anatomical problems, most notably cervical length in the setting of risk factors for preterm birth or cervical insufficiency.
• Ultrasound monitoring of fibroids and/or ovarian cysts is also important, but this is limited at later gestationa