Obstetric Ultrasound

//Obstetric Ultrasound
Obstetric Ultrasound 2017-12-14T02:05:14+00:00

Obstetric Ultrasound

 

Obstetric ultrasonography is the use of medical ultrasonography in pregnancy, in which sound waves are used to create real-time visual images of the developing embryo or fetus in its mother’s uterus (womb). The procedure is a standard part of prenatal care in many countries, as it can provide a variety of information about the health of the mother, the timing and progress of the pregnancy, and the health and development of the embryo or fetus.

Pregnant women should have routine obstetric ultrasounds between 18 weeks and 22 weeks gestational age to confirm pregnancy timing, to measure the fetus so that growth abnormalities can be recognized quickly later in pregnancy, and to assess for congenital malformations and multiple pregnancies (i.e. twins). Performing an ultrasound at the early stage of pregnancy can more accurately confirm the timing of the pregnancy and can also assess for multiple fetuses and major congenital abnormalities at an earlier stage. 

 

First trimester

In the first trimester, a standard ultrasound examination typically includes:

  • Gestational sac size, location, and number
  • Identification of the embryo and/or yolk sac
  • Measurement of fetal length (known as the crown-rump length)
  • Fetal number, including number of amnionic sacs and chorionic sacs for multiple gestations
  • Embryonic/fetal cardiac activity
  • Assessment of embryonic/fetal anatomy appropriate for the first trimester
  • Evaluation of the maternal uterus, tubes, ovaries, and surrounding structures
  • Evaluation of the fetal nuchal fold, with consideration of fetal nuchal translucency assessment

Second and third trimester

In the second trimester, a standard ultrasound exam typically includes:

  • Fetal number, including number of amnionic sacs and chorionic sacs for multiple gestations
  • Fetal cardiac activity
  • Fetal position relative to the uterus and cervix
  • Location and appearance of the placenta, including site of umbilical cord insertion when possible
  • Amnionic fluid volume
  • Gestational age assessment
  • Fetal weight estimation
  • Fetal anatomical survey
  • Evaluation of the maternal uterus, tubes, ovaries, and surrounding structures when appropriate

Dating and growth monitoring

Gestational age is usually determined by the date of the woman’s last menstrual period, and assuming ovulation occurred on day fourteen of the menstrual cycle. Sometimes a woman may be uncertain of the date of her last menstrual period, or there may be reason to suspect ovulation occurred significantly earlier or later than the fourteenth day of her cycle. Ultrasound scans offer an alternative method of estimating gestational age. The most accurate measurement for dating is the crown-rump length of the fetus, which can be done between 7 and 13 weeks of gestation. After 13 weeks of gestation, the fetal age may be estimated using the biparietal diameter (the transverse diameter of the head, across the two parietal bones), the head circumference, the length of the femur, the crown-heel length (head to heel), and other fetal parameters.  Dating is more accurate when done earlier in the pregnancy; if a later scan gives a different estimate of gestational age, the estimated age is not normally changed but rather it is assumed the fetus is not growing at the expected rate.

Not useful for dating, the abdominal circumference of the fetus may also be measured. This gives an estimate of the weight and size of the fetus and is important when doing serial ultrasounds to monitor fetal growth.    https://en.wikipedia.org/wiki/Obstetric_ultrasonography