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Moronacity Health Journal » Pregnancy

Second Trimester Ultrasound

By Diane Ursu
Second Trimester Ultrasound; Source:  Sam PullaraSecond trimester ultrasound is the most common pregnancy ultrasound. It is typically done between 18 and 22 weeks of gestation to determine if the fetus is developing properly. It is a very thorough examination in which pictures of many body parts are obtained.

Second Trimester Ultrasound Preparation

Expectant mothers are asked to fill their bladders prior to the second trimester ultrasound. This is a necessary preparation that greatly affects the outcome of the examination. The full bladder pushes the fetus up and out of the mother’s pelvis so the pelvic bones do not obstruct the view – ultrasound cannot see through bone. The full bladder also creates a sonographic window that allows the sonographer to examine the cervix and the placental position. In addition, the bladder may be helpful in visualizing the ovaries to determine if there are any masses or cysts that need immediate medical attention.

The following bladder preparation ensures that the bladder will be full in time for the ultrasound.
  • One hour before the exam, completely empty the bladder and begin drinking 32 ounces of water, to be completed within 10 minutes.
  • The 32 ounces of water should be completely drunk by 50 minutes prior to the exam.
  • Do not use the restroom until told to do so by the sonographer. If the bladder is not adequately filled for the exam, the ultrasound examination may be rescheduled for another day.
Uterus and Adnexa

The sonographer begins the ultrasound by examining and taking a series of pictures of the uterus, placenta, and the adnexa. The adnexa are the areas on either side of the uterus, containing the ovaries. A transvaginal ultrasound may be done to more thoroughly examine the cervix and the placenta, especially if the placenta is in a low position. The amniotic fluid index (AFI) is taken by measuring a pocket of fluid in each quadrant of the gestational sac.

Fetal Growth

The sonographer determines the approximate age and weight of the fetus by taking several body measurements. The calculated due date is compared with that of the first trimester ultrasound or last menstrual period dating (LMP). The following measurements are obtained:
  • head circumference;
  • biparietal diameter – from the inner edge of the far side of the skull to the outer edge of the near side of the skull, in relation to the ultrasound camera;
  • abdominal circumference – basically the measurement of the fetus’ waist;
  • femur length – the measurement of the upper leg bone from the hip to the knee.
Head Anatomy

The head and brain anatomy are extensively surveyed because this is the part of the body that is most likely to exhibit signs of genetic defects, such as Down Syndrome. Images of the following head anatomy is obtained:
  • choroid plexus;
  • lateral ventricles;
  • cisterna magna;
  • cavum septum pellucidum (CSP);
  • cerebellum;
  • nuchal fold (fold of skin on the back of the neck);
  • eye orbits;
  • lips and nose;
  • profile, including the nasal bone.

Several pictures of the spine are acquired to rule out abnormalities such as spina bifida. A lengthwise image is taken to demonstrate that full spine from the neck to the tip of the tailbone. Transverse, or cross-sectional, images are taken at the level of the neck or clavicles, the heart, the kidneys, and the iliac bones.

Chest and Abdomen

Several organs are examined in the chest and abdomen. Some sonographers extensively examine the heart, while others obtain only the four-chamber view. The following are obtained:
  • heart rate;
  • four-chamber heart;
  • left ventricular outflow tract (aorta);
  • right ventricular outflow tract (pulmonary arteries);
  • diaphragm;
  • stomach;
  • kidneys;
  • bladder;
  • umbilical cord insertion into the abdomen.
The second trimester ultrasound examination may take as little as 30 minutes, but often takes as much as an hour. Fetal position and movement can make it more difficult to obtain all of the necessary images. In some cases, the mother will be scheduled for a follow-up ultrasound examination if some of the images cannot be taken.


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