Age, obesity and uterine contractility…

small_127813925During the last week, two important papers from the Birthplace team have been published.

The impact of maternal obesity on intrapartum outcomes in otherwise low risk women: secondary analysis of the Birthplace national prospective cohort study, which has been available online for a few months (and discussed here), was published in print form in the BJOG (Hollowell et al 2013).

Then, just a few days later, The effect of maternal age and planned place of birth on intrapartum outcomes in healthy women with straightforward pregnancies: secondary analysis of the Birthplace national prospective cohort study (Yangmei et al 2014) was published in BMJ Open.


Important research

These papers are important for lots of reasons.

I was particularly interested to read the latest paper because I have recently been thinking a lot about the issue of alleged poor uterine contractility in women who are larger and/or older than average.

I have also been discussing this with a number of other midwives, and I am particularly not as convinced as some of my esteemed colleagues that overweight women are intrinsically at risk from poor uterine contractility.

It’s just not what I (and apparently a good few of my colleagues) have seen in practice, sorry.

And yes, I know that what I’ve seen in practice is only my experience, but several aspects of national guidance relating to this area are based on the expert opinion of certain other practitioners, so I feel justified in throwing mine into the mix.



This is a complex issue and many possibilities exist, which are not necessarily mutually exclusive. Some possibilities to think about here include:

  • Some women have longer labours than others, and this is merely reflective of a normal range.  How boring it would be if every woman had the same labour!  If there are differences, is this actually a problem, or do we just need to adapt our thinking?
  • If there are differences, is it possible that these might be caused not by overweight and age per se, but by the differences in the environments in which we work, which (among many other elements) will include our perception of whether or not certain physical characteristics (such as age and size) are risk factors?
  • Could the kind of care – which might include, for instance, the degree of emphasis that the attendant places on the importance of creating a space that is more likely to enable women to release oxytocin – make a difference?
  • The mere act of labelling someone as ‘at risk’, let alone the increased monitoring which is offered to women who are perceived to be at increased risk, might – understandably – cause those women to feel anxious.  This might, in turn, make it harder for them to relax and release the oxytocin which promotes uterine contractility…

It might well be that, for some reason that we have yet to uncover, women who weigh more or are older have poorer uterine contractility.  But this also might be iatrogenic and/or environmentally dependent.

It might be caused, in part, with the growing focus on so-called clinical complexity, and the effect that this has on practitioners’ expectations.

Or by size or weight bias, which we know is prevalent in maternity and health care.

As far as I can see, the theory of reduced uterine contractility is just one theory which isn’t evidence-based.

And more studies carried out in medicalised environments wouldn’t necessarily help, anyway. Especially when the labelling that exists in such environments is clearly part of the problem:


“An age-related increase in augmentation is consistent with evidence of poorer uterine function at older ages,34 longer labours34 and an increased incidence of prolonged labour,35 ,36 but the reasons for a steeper increase in augmentation with age in non-OU settings are unclear.

It has been suggested that labelling of older women as ‘higher risk’ and/or heightened concern about the safety of older nulliparous women, particularly those who have required fertility treatment, may result in increased rates of caesarean section for non-medical reasons,20 ,32 ,33 ,37 and it is possible that similar factors affect midwives’ decision-making regarding transfer for failure to progress, or for other reasons.

Intrapartum transfers from midwifery units in the Birthplace study have been shown to increase significantly with age in nulliparous women29 and, once transferred, women are ‘exposed’ to the higher intervention rates found in OUs.”  (Yangmei et al 2014)


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Objectives To describe the relationship between maternal age and intrapartum outcomes in ‘low-risk’ women; and to evaluate whether the relationship between maternal age and intrapartum interventions and adverse outcomes differs by planned place of birth.

Design Prospective cohort study.

Setting Obstetric units (OUs), midwifery units and planned home births in England.

Participants 63 371 women aged over 16 without known medical or obstetric risk factors, with singleton pregnancies, planning vaginal birth.

Methods Log Poisson regression was used to evaluate the association between maternal age, modelled as a continuous and categorical variable, and risk of intrapartum interventions and adverse maternal and perinatal outcomes.

Main outcome measures Intrapartum caesarean section, instrumental delivery, syntocinon augmentation and a composite measure of maternal interventions/adverse outcomes requiring obstetric care encompassing augmentation, instrumental delivery, intrapartum caesarean section, general anaesthesia, blood transfusion, third-degree/fourth-degree tear, maternal admission; adverse perinatal outcome (encompassing neonatal unit admission or perinatal death).

Results Interventions and adverse maternal outcomes requiring obstetric care generally increased with age, particularly in nulliparous women. For nulliparous women aged 16–40, the risk of experiencing an intervention or adverse outcome requiring obstetric care increased more steeply with age in planned non-OU births than in planned OU births (adjusted RR 1.21 per 5-year increase in age, 95% CI 1.18 to 1.25 vs adjusted RR 1.12, 95% CI 1.10 to 1.15) but absolute risks were lower in planned non-OU births at all ages. The risk of neonatal unit admission or perinatal death was significantly raised in nulliparous women aged 40+ relative to women aged 25–29 (adjusted RR 2.29, 95% CI 1.28 to 4.09).

Conclusions At all ages, ‘low-risk’ women who plan birth in a non-OU setting tend to experience lower intervention rates than comparable women who plan birth in an OU. Younger nulliparous women appear to benefit more from this reduction than older nulliparous women.

Strengths and limitations of this study

  • The study was based on a large, nationally representative cohort of ‘low-risk’ women, with high-quality data collected prospectively.

  • The number of women aged over 40 was relatively small, so the study had limited power to explore effects in women over 40, particularly in non-obstetric unit settings.

  • Planned births in non-obstetric unit settings were combined; graphical plots indicated that this was reasonable but important differences between settings cannot be ruled out.

The paper can be read in full here

photo credit: Über Times  via photopin cc

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