Natural length of pregnancy thought to vary by up to five weeks

Posted 07/08/2013

A recent study has looked at the gestation period in 125 women from the time of actual conception to delivery. It is the first study that has pinpointed the exact time of conception or implantation. Previously, the variability of gestation between women was thought to result from errors in establishing the exact gestational age (or the exact time of conception).This study found that the length of time to achieve implantation varied between individuals and that embryos that took longer to implant tended to have longer overall gestation periods.  It found that an individual was likely to have broadly consistent lengths of gestation in a number of pregnancies so there would appear to be consistency in individuals, but an unexpectedly wide variation between different woman by as much as 37 days.These findings raise queries about how useful it is to suggest a ‘due date’. It is potentially important to know when someone is really likely to naturally deliver as it could help clinicians to decide when intervention might be needed. Although this study is a relatively small one, it has been welcomed with interest by the Royal College of Obstetricians and Gynaecologists.Trefine Maynard, a clinical negligence solicitor at Ashtons Legal, said: “This study is fascinating. So much more can be established about a baby’s health in the womb during scans throughout the pregnancy than used to be possible, but it is all still based on a pre-determined ‘average’ length of pregnancy. If these findings are confirmed, then it throws considerable doubt on treatment based on an ‘average’ if the real range of natural length of pregnancy can vary by over a month. It may also provide an interesting basis for review of much of the ‘standards’ in  a number of different areas of medicine that are all too often based on an ‘average’ norm. As we learn more about individual differences, doctors may well recognise that what is normal and healthy for one individual is different from what is normal for another. Ultimately this may avoid unnecessary and potentially harmful treatment for those who do not actually require it.  In pregnancy, the lack of accuracy of a using an average is illustrated by the fact that only 4% of women deliver when predicted and only 70% within 10 days of their so called ‘due date’. This leads to doubts about the value, let alone the accuracy, of using a ‘due date’ as any kind of indicator for care and treatment.”