- Human gestation is not actually 9 months long. A healthy baby can be born at anywhere between 37-42 weeks gestation, on average. Some moms can go as long as 43 weeks as long as they are closely monitored by health care professionals.
- There is more than one way to calculate due date:
Based on LMP:Based on date of Conception:
If your cycles are regular and 28 days long, then you can determine your due date by adding 9 months and 7 days to the first day of your last menstrual period (LMP). For example, if your LMP began on September 5, then your expected due date (EDD) would be June 12 of the following year.
If your cycles are 28 days long and you know your date of conception, you can determine your due date by first subtracting 7 days, and then adding 9 months. However, this method will probably not work for most women unless they have had intercourse only once during the fertile period of that cycle and remember the date.
- Ultrasound Scan:
An ultrasound can determine the development of the baby and provide a more accurate due date. This method is superior to other methods because the doctor is able to examine and measure each of the baby's organs on ultrasound screen. These measurements can then help in determining the size of the baby, i.e. stage of fetal development, and consequently the due date. If you have more than one scan, it is possible that each of your ultrasound scans gives a different due date. The date computed from the last ultrasound scan is likely to be the most accurate. Again, remember that these dates are simply estimates, and therefore are only indicative of the actual delivery date.
- Only five percent of babies in the United States arrive on their estimated due date.
That is why there is nothing special about today.