The term due date creates a lot of misconceptions. It implies that you are due to have your baby by a specific date, but this is not the case. You are not “due” to have your baby by 40 weeks. You are not “overdue” when you hit that magic date. Every pregnancy will last a different amount of time. Anywhere between 37 and 43 weeks is considered normal. 80% of babies are born within the 2 weeks before or after 40 weeks and only about 5% of babies are born on their “due dates”.
There are a few things to consider about due dates. First we say that pregnancy lasts 40 weeks. This isn’t actually the case.
This is based on pregnancy lasting approximately 10 moon cycles which would be 40 weeks. The average pregnancy is actually 40 weeks + 3 days and the average first time pregnancy is actually 41 weeks +1 day. Therefore as a first time mom, if you are at 40 weeks + 8 days you haven’t even gone beyond the average.
The second issue is that we use averages as if they mean that is something to be expected or ideal. There is nothing ideal about being average.
Average only means that if you take all women and average out when they give birth that the average will be on a certain date. It could be that no women would actually birth on that date and it will still be the average. It just means that for everyone that is 14 days before, there is one that is 14 days after. Another way of stating that is 50% of babies will be born before their due date and 50% will be born after. We are not striving to be in the middle, it just gives us a time frame to expect for. Anytime in the 3 weeks before or after that date could be when your baby decides to arrive.
The third problem with due dates is how we calculate them.
Most dates are calculated based on the first day of your last menstrual period. We add 40 weeks to that number and say that is your due date. This does not factor in ovulation and conception dates. Every women’s cycle is different, some are 28 days, some are 35. We typically ovulate in the middle of our menstrual cycles but this is not necessarily the case for all women. Ovulation could be on day 11 or day 21 or anywhere in between. That gives us a 10 day discrepancy on when you would actually hit the 40 week pregnant mark. Adding 38 weeks to the date of conception, if known, would be a more accurate way of determining dates, but again that date does not mean you are due to have your baby by then, it would just give you a better time range of 3 weeks before or after.
Then there is ultrasound. This is the forth confusing factor for women when being told their dates.
Many women will have their dates changed based on ultrasound. The flaw here is that again we are basing this on averages. When measuring a fetus and say “based on the size of the fetus it is X days/weeks old, therefore your due date is…” assumes that all people grow and develop at the same rate. This would be like saying well you are 4 foot 10 today so that means you are 12 years and 52 days old. It could also be based on stage of organ development, again like saying, OK you have now developed the beginning of breast tissue so you are 12 years and 82 days old. Everyone grows and develops within individual time lines. Averages again don’t mean anything. An average just means that if you take the entire population and plot them out, we average at a certain number. Most are above or below and a few will actually fall exactly on the average. To say your baby is a certain age because of what the average is not an accurate way of estimating a pregnancy. This also doesn’t factor in the size of the parents. Can we expect a baby born to two six foot parents to be the same size as a baby born to two 5 foot patents. How can we say they will be the same size on the same date when one will end up being 9 pounds and the other barely 6 pounds by the end of the pregnancy. There is also human error when looking at measuring crown to rump length and may get completely different measurement with different technicians. Ultrasound can be off by as much as 4 weeks when dating a pregnancy.
So where does that leave us? We need to be a lot more relaxed with our expectations about due dates.
I always advise moms to be ready by 37 weeks and then add 3 weeks to the 40 week date so that they don’t start to feel like the baby is going to stay in forever. When we get in our heads that we will have our baby by a certain date we can start to get frustrated and upset about still being pregnant. When people ask my dates I typically give them a month or will say something like early October so anytime from mid September to late October so that there is less focus on a specific date or time frame.
The next question is standard practice of induction. Depending on the standard practice in your area you may be told you must have your baby by 40weeks, 40weeks+10days or 42 weeks.
If your care provider wants you to have your baby by your 40 week date that means you have a 50% chance of being induced. My opinion is don’t be pressured into an early induction. One, it is unlikely that your dates are accurate and two that date does not mean anything but that the average baby will be born around that time. I have been informed that the risk of a stillborn baby is the same at 38 and 42 weeks and that 37 weeks is the same risk as 43 weeks. If 38 weeks is considered acceptable 42 weeks should be the same.
Unless there are clear signs of distress and that continuing the pregnancy would be unhealthy, I would avoid an early induction. Induced labors can lead to a complicated and traumatic births and a much higher risk of distress to the baby and caesarean surgery. Many babies are being born today premature that were supposedly 40weeks+10days. This premature induction can lead to health problems in infancy and in the future. Science isn’t 100% sure what triggers labor but it has been suggested that there is a factor that is released by the baby when it’s lungs are ready for the outside world. Forcing them out too early can lead to respiratory distress and problems later in life. Only your baby knows the perfect time to be born and just like everything else in birth we need to surrender to nature’s knowledge if we want to allow it to progress without complications.
For more information on due dates visit: http://www.midwiferytoday.com/articles/timely.asp