Since blood and daily urine excretion of creatinine shows minimal fluctuation, creatinine excretion is useful in determining whether 24-hour urine specimens for other analytes (e.g., protein) have been completely and accurately collected. To view specimen requirements and codes please Select a regional laboratory.
Ultrasound is almost foolproof at diagnosing twins, but the greater the number of babies, the less accurate the ability to detect how many there are. It's possible to see twins (or more) on a scan at around six weeks, though one baby may be missed at this early stage. Sometimes a heartbeat is seen in one sac, but not in the other. Rescanning in a week or two may reveal a second heartbeat, or the scan may show that one sac is growing and the other still empty.
The average twin is delivered after 36 weeks of gestation. Contrast that with the average for non-twins: 40 weeks. In other words, twins tend to be delivered a full month earlier than non-twins.