During a transabdominal ultrasound, a conductive gel is placed on the abdomen, and a hand-held wand which ＿＿（21）＿＿ sound waves is moved in a systematic pattern in an effort to examine the internal structures. This test requires a ＿＿（22）＿＿ bladder so that the organs in question are lifted out of the pelvis as the bladder fills. The patient may be asked to drink two to three glasses of water starting an hour ＿＿（23）＿＿ the test. This method works best for more advanced pregnancies when the fetus is well developed. The physician may have a vaginal scan performed during the first trimester to make sure the pregnancy is within the uterus and to rule out an ectopic pregnancy. It is also possible to visualize the fetal heartbeat and movement, and, thus, rule out a miscarriage. The vaginal scan can also determine if there is more than one pregnancy within the uterus. During the remainder of the pregnancy, scans may be used to look for problems, ＿＿（24）＿＿ the age and development of the fetus, check out its position within the uterus, and, between 16 and 20 weeks, determine the fetal sex. There is no risk to the woman or her developing fetus with ultrasound, and it is not uncomfortable. Ultrasound examinations aid doctors in establishing an accurate ＿＿（25）＿＿ date. The estimated date of delivery can now be predicted within two to four days if the initial ultrasound is performed early in pregnancy.