The wider window
Having attended a seminar on post dates pregnancy run by midwife and researcher Sara Wickham, Forfar service user representative and doula Karen Law calls on midwives and women to broaden their perception of what a ‘due date’ actually means.
It was with great excitement that I set off for Edinburgh with Phyllis Winters (midwifery team leader at Montrose Maternity Unit) on Monday 3rd November 2008. We were fortunate to have places at a small seminar on Post Dates pregnancy. This was being run by midwife and teacher Dr Sara Wickham after the completion of her PhD thesis on midwifery knowledge in relation to ‘post-term’ pregnancy. As we drove down we talked non-stop; it is so refreshing to spend time with someone who shares your beliefs about childbirth!
Around 30 of us attended the seminar at Napier University – experienced midwives, student midwives, doulas, homeopaths and National Childbirth Trust antenatal teachers. Sara is an eloquent speaker, animated and engaging. I was a little disappointed that she had no real new groundbreaking information to give us, but relieved to find that nothing I hold dear has been changed by any new evidence, and reassured that many of us are on the same page working towards improving maternity care.
When women are pregnant, they are given an ‘Estimated Date of Delivery’ (EDD). Having this helps women to plan and prepare for their baby’s birth. It is also important for health service staff monitoring the baby’s development throughout pregnancy. Unfortunately this is far from an exact science…
Aristotle first documented the average length of pregnancy as being ten lunar months, which is widely accepted as being 280 days, and Naegele's Rule calculates the baby's due date by adding 7 days and 9 months to the first day of a woman's last menstrual period before becoming pregnant. Sara pointed out that neither of these methods was arrived at using any reasonable research based evidence. In fact, Naegele's was based on observation of only 100 women in 1838!
A newer method is Mittendorf-Williams Rule (1990). While some studies have found Mittendorf-Williams to be more accurate than Naegele's Rule in calculating due date, it does not tend to be used. Sara suggests this is all about politics, in particular power and finance.
Ultrasound can be inaccurate for sizing and dating after the first trimester, and the routine use of ultrasound scanning is not recommended by the World Health Organization. (See the AIMS booklet ‘Ultrasound? Unsound’ for more information.)
Contentious issue
Women are generally prepared by services for an induction if they go more than two weeks beyond the fixed point of their Estimated Date of Delivery. This is a contentious issue, as induction is a medical procedure which carries risks and interferes with the body’s natural cycle. So where did this come from, and is it still relevant?
In the 1960's two small studies suggested that prolonged pregnancy may lead to a higher incidence of neonatal death, so the WHO (World Health Organization) and IFGO (International Federation of Gynaecology and Obstetrics) defined pregnancy which extended past 42 weeks as prolonged. However Sara says that these two studies were so bad in their methodology that they are not included in modern reviews. Coincidently, the Syntocinon Pump was developed in the 1960's and made induction of labour suddenly available.
Sara’s research finds that a significant number of randomised controlled trials have failed to show that Induction of Labour is beneficial. While meta-analysis of many small trials seems to show that Induction of Labour is marginally beneficial, the largest trial within the meta-analysis showed no benefit. Sara argues that only methodologically sound studies should be included in a meta-analysis.
A woman’s genetic factors such as country of origin, height and ethnicity can also have an effect on gestation. Currently Sara can find no research on this but she has acquired many anecdotal stories which show correlation.
Another issue is the actual time of conception. When considering two women with an identical Last Menstrual Period date, we cannot expect the woman with a 24 day cycle to birth her baby at the same time as one who has a 35 day cycle, yet this is not usually factored in when estimating due dates. This then impacts on our estimating the date of birth.
Let nature take its course
On the whole, Sara finds that evidence suggests it may be better to let nature take its course and to wait for spontaneous labour in otherwise healthy pregnancies. She suggests her website and the AIMS booklet ‘Induction – Do I really need it’ as further reading. She stressed the importance of considering what is normal for each woman, normal under the circumstances and normal according to Obstetrics.
Sara concluded by suggesting something Phyllis and I had agreed upon on our journey to the seminar. As midwives, doulas, support group organisers and women, we should not be focusing on the 40 week fixed date but should be using our communication skills to encourage women to expect their baby “sometime between 37 and 42 weeks”. When we continually think and talk about this wider window so that we overcome previous conditioning, women will be less stressed as they go past the ‘magic’ 40 week mark, and no baby less than 42 weeks will be considered ‘overdue’.
Karen Law is a user representative on the Angus Maternity Services Liaison Committee and is also a doula.
Acknowledgements
Thanks to organisers of the event from Napier University, AIMS, the Birth Resource Centre and the Scottish Birth Teachers Association.
Further information
• Sara Wickham’s website
• AIMS booklets
• The Mitterndorf study is reported in ‘The length of uncomplicated human gestation’, Obstetrics & Gynaecology (1990), 75(6), pp.929-932.
