When are ultrasounds usually performed during pregnancy?

Since the late 1950’s ultrasonography has become a very useful diagnostic tool in Obstetrics.  The technology has advanced greatly in its half-century lifespan.  Today’s equipment is able to provide real-time continuous pictures of the moving fetus.  These images are created from high frequency sound waves emitted from a transducer that is placed in contact with the abdomen and moved around like a flashlight all around the uterus.  Ultrasound beams can the fetus in thin slices and are reflected back on the transducer.  The data obtained from different reflections are put back together as a picture on the monitor.  This allows the physician to view malformations in the fetus, take measurements to assess gestational age, size and growth, and assess movements such as heart beat. 

Ultrasound scans are currently considered to be a safe, non-invasive, accurate and cost-effective way to investigate the fetus. It has progressively become an indispensable obstetric tool and can play an important role in the care of every pregnant woman.





The main uses of ultrasonography are in the following areas:

1.  Confirm Pregnancy:  At as early as four and a half weeks of gestation, the gestational sac can be seen on an ultrasound.  At five and a half weeks, the embryo can be measured and observed.

2.  Vaginal bleeding in early pregnancy:  In the presence of first trimester bleeding, ultrasonography is indispensable in the early diagnosis of ectopic pregnancies and molar pregnancies.

3.  Diagnosis of fetal malformation:  Abnormalities in the fetus, such as hydrocephalus, anencephaly, myelomeningocoele, achondroplasia and other dwarfism, spina bifida, exomphalos, Gastroschisis, duodenal atresia and fetal hydrops can be often be detected via ultrasound within 20 weeks.  Ultrasound can also assist in other diagnostic procedures in prenatal diagnosis such as amniocentesis, chorionic villus sampling, cordocentesis (percutaneous umbilical blood sampling) and in fetal therapy.  Ultrasound may also sometimes be used during the first trimester to enable detection of Down syndrome fetuses. 

4.  Placental localization:  Ultrasound has become critical in identifying the site of the placenta.  This assists the physician with making a diagnosis or an exclusion of placenta previa and other placental abnormalities in conditions such as diabetes, fetal hydrops, Rh isoimmunization and severe intrauterine growth retardation.

5.  Determination of age and fetal size:  Body measurements reflect the age of the fetus. This is particularly true in early gestation. In patients with uncertain last menstrual periods, such measurements must be made as early as possible in pregnancy to arrive at a correct dating for the patient.

6.  Determination of fetal gender.  Many women are able to accurately determine the gender of their baby well in advance using ultrasound.

7.  Multiple pregnancies:  Ultrasound is invaluable in determining the number of fetuses.

8.  Other Diagnoses:  Ultrasound can be used alongside other methods to confirm intrauterine death, confirm fetal presentation, evaluate fetal movements, tone and breathing, and diagnose uterine and pelvic abnormalities during pregnancy such as fibromyomata and ovarian cyst.

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