Pregnancy ultrasound guide

A short history of the development of ultrasound in pregnancy can be found in the History pages.
Ultrasound scan is currently considered to be a safe, non-invasive, accurate and cost-effective investigation in the fetus.
The viability of the fetus can be documented in the presence of vaginal bleeding in early pregnancy.
The timing of a positive pregnancy test may also be helpful in this regard to assess the possible dates of conception.
Many structural abnormalities in the fetus can be reliably diagnosed by an ultrasound scan, and these can usually be made before 20 weeks. Read also: Soft Markers - A Guide for Professionals and Ultrasonographic "soft markers" of fetal chromosomal defects.
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. Excessive or decreased amount of liquor (amniotic fluid) can be clearly depicted by ultrasound.
With specially designed probes, ultrasound scanning can be done with the probe placed in the vagina of the patient. Vaginal scans are also becoming indispensible in the early diagnosis of ectopic pregnancies. Doppler ultrasound is presently most widely employed in the detection of fetal cardiac pulsations and pulsations in the various fetal blood vessels. Most experts do not consider that 3-D and 4-D ultrasound will be a mandatory evolution of our conventional 2-D scans, rather it is an additional piece of tool like doppler ultrasound. A short history of the development of 3-D ultrasound in pregnancy can be found in the History pages. There is no hard and fast rule as to the number of scans a woman should have during her pregnancy. One should not dwell too much on the definitions or guidelines for a level II ultrasound scan.

That a pregnancy should be scanned at 18 to 20 weeks as a rule is gradually becoming a matter of routine practice. Although certain harmful effects in cells are observed in a laboratory setting, abnormalities in embryos and offsprings of animals and humans have not been unequivocally demonstrated in the large amount of studies that have so far appeared in the medical literature purporting to the use of diagnostic ultrasound in the clinical setting. The greatest risks arising from the use of ultrasound are the possible over- and under- diagnosis brought about by inadequately trained staff, often working in relative isolation and using poor equipment.
A discussion on the various possible effects of ultrasound on the human fetus can be found here. It should be bornt in mind that prenatal ultrasound cannot diagnose all malformations and problems of an unborn baby (reported figures range from 40 to 98 percent), so one should never interpret a normal scan report as a guarantee that the baby will be completely normal.
If you are interested to find out more about a particular fetal anomaly, take a look at this compilation of Web pages which describe in some detail specific congenital anomalies that are diagnosable by ultrasound. It has progressively become an indispensible obstetric tool and plays an important role in the care of every pregnant woman. A visible heartbeat could be seen and detectable by pulsed doppler ultrasound by about 6 weeks and is usually clearly depictable by 7 weeks. The diagnosis of missed abortion is usually made by serial ultrasound scans demonstrating lack of gestational development.
A positive pregnancy test 3 weeks previously for example, would indicate a gestational age of at least 7 weeks.
Further developments in doppler ultrasound technology in recent years have enabled a great expansion in its application in Obstetrics, particularly in the area of assessing and monitoring the well-being of the fetus, its progression in the face of intrauterine growth restriction, and the diagnosis of cardiac malformations.
Ultrasound can also very importantly confirm the site of the pregnancy is within the cavity of the uterus. For example, if ultrasound scan demonstrates a 7mm embryo but cannot demonstrable a clearcut heartbeat, a missed abortion may be diagnosed.
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. Using computer controls, the operator can obtain views that might not be available using ordinary 2-D ultrasound scan.

3-D ultrasound appears to have great potential in research and in the study of fetal embryology. Otherwise a scan is generally booked at about 7 weeks to confirm pregnancy, exclude ectopic or molar pregnancies, confirm cardiac pulsation and measure the crown-rump length for dating. In fact professional bodies such as the American Institute of Ultrasound in Medicine does not endorse or encourage the use of these terms. The use of high intensity ultrasound is associated with the effects of "cavitation" and "heating" which can be present with prolonged insonation in laboratory situations. In such cases, it is reasonable to repeat the ultrasound scan in 7-10 days to avoid any error.
3-dimensional ultrasound is quickly moving out of the research and development stages and is now widely employed in a clinical setting. The most common reason for having more scans in the later part of pregnancy is fetal growth retardation. In the latter part of pregnancy measuring body parameters will allow assessment of the size and growth of the fetus and will greatly assist in the diagnosis and management of intrauterine growth retardation (IUGR). The sonographer may use a special scanning probe, which is placed in your vagina, as ordinary equipment may not be able to detect your baby yet.Dating or 12-week scanThis is offered to help doctors accurately date your pregnancy and is done between 11 and 16 weeks.
You will probably have a 'pelvic' ultrasound, where the transducer is placed on the skin over your pelvis.Nuchal scanDone between 10 and 13 weeks, this scan tells you your risk of having a baby with Down's syndrome by measuring the size of the groove at the back of your baby's neck often done in conjunction with the dating scan. The Links section above also furnish you with some of the best reading and information on the Internet concerning the various aspects of ultrasonography in pregnancy.

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