Your 12-week pregnancy dating scan
During the course of the pregnancy, every mother should have at least two scans. These help to ensure the pregnancy goes smoothly, and to identify any problems ahead of time. The dating scan is generally the first ultrasound that every mother-to-be will have. While many women will have a good idea of when they had their last menstrual period, another portion will be far less certain.
This can be due to a number of factors, including whether the pregnancy was planned or not, and if the mother often has irregular periods. The scan also gives a due date, which is sometimes a small range of dates due to a difference with your own dating attempt. An accurate due date is dating scan time frame so that, in the event of being overdue, your doctor knows whether you are drastically overdue or simply a few days late.
Your doctor will ask you questions about when you had your last menstrual period, and estimate that ovulation occurred 14 days into the cycle, but some mothers may be unsure. However this is not usually a problem, as the best time for a dating scan falls between 8 and 12 weeks, a month-long period. Dating scans are much less reliable after 13 weeks because at this stage babies often start growing at different rates. These are dating scan time frame calculations such as the length from crown to rump head to the end of the bottomthe femur length longest bone in the bodyand the head circumference.
Some of these and other measurements are most useful after 13 weeks, which is beneficial for a late dating scan. For these purposes, the sonographer looks for the foetal heartbeat and any currently visible abnormalities. If the heartbeat cannot be detected then more tests have to be done, but this does not necessarily indicate a problem: An experienced sonographer can often find any major irregularities like limb deformities.
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