Ultrasound

Ultrasound is a diagnostic imaging technique used to obtain information about the fetus and its surroundings. 超声波技术利用从皮肤表面通过子宫传播的高频声波。. Depending on the density of the underlying structures, the sound waves are then returned, producing an image on a small screen.

Ultrasound was first employed by the military as a means of locating submarines. The idea was further expanded and used by industry as a means of detecting flaws in dense or solid structures. 20世纪60年代早期，超声波首次用于产科，用于定位胎盘(胎儿)和胎儿的位置. Today it is possible, because of advances made in the instruments, to learn extremely important information about the fetus and its environment.

进行超声波检查最常见的原因是确定婴儿的大致年龄和位置，并确保婴儿正常生长.

Age can be determined early in the pregnancy (2 to 3 months) by measuring the length of the baby. Later, at 4 to 7 months, age is derived by measurements of the head and the length of the femur, the long bone inside the thigh. These measurements are then compared to a table that lists averages of normal baby growth.

With the use of ultrasound, the amount of fluid surrounding the baby can be seen as well as the placenta, or afterbirth, and the placenta's position. 这些信息有助于确定您将采用何种分娩方式(阴道分娩还是剖宫产)，以及分娩后婴儿是否需要立即进行任何特殊的医疗护理. (Early in pregnancy, it may be necessary to scan with a special transducer placed in the vagina to see the baby.)

The most common reasons for a doctor to request ultrasound are:

• To determine your due date through measurements of the fetus. Ultrasound dating has been proven to be more accurate than menstrual dating, especially if done early in pregnancy.
• To confirm an early pregnancy.
• To evaluate fetal growth.
• To determine if there is a normal amount of amniotic fluid.
• To observe fetal movement and heart activity.
• To select the best site for amniocentesis.
• To survey fetal anatomy

目前诊断超声仪器的典型强度暴露对患者或仪器操作人员造成的生物效应尚未得到证实. Although the possibility exists that such biological effects may be indicated in the future, current data indicate that the benefits to patients of the prudent use of diagnostic ultrasound outweigh the risk, if any, that may be present.

腹部超声检查很少或没有疼痛，尽管保持膀胱充盈可能会有一些不适. 一种凝胶状材料被涂在你的腹部，然后仪器被放置在皮肤表面，以提供换能器和皮肤之间更好的接触. This gel may feel slightly cold and, even though it wipes off easily, it is a good idea to wear clothing that is easily washable.

Sometimes it is possible to see the sex of the baby and sometimes it is not. If the baby is lying in an inconvenient position, the baby's sex cannot be determined.

检测异常的能力取决于异常的大小和婴儿在子宫中的位置. Therefore, it is possible that some abnormalities may not be detected.

Please arrive with a full bladder. It is helpful to have a full bladder prior to ultrasound. Therefore, drinking 4 to 6 glasses of water one hour before and not voiding just prior to the procedure is wise. 这被发现是非常有用的，因为满膀胱有助于将子宫从骨盆中抬起，以便更完整地看到. It has also been found that because sound passes easily through fluid, a more clearly defined picture of the early pregnancy is made possible.

The average obstetrical ultrasound exam at the Regional Perinatal Center takes between fifteen and thirty minutes. Complicated cases and multiple gestations take up to an hour or more. 有一些因素限制了检查的质量，包括母亲的体型、婴儿的体位和胎龄. These can also lead to an increase in the length of the exam.

You may bring no more than two adults to watch the exam with you. We prefer that this includes the baby's father or some other significant person. We prefer that children under the age of 10 not attend.