I’ve not quite got to the point where I need a ‘language rant of the month’ as well as ‘quote of the month’, but regular readers of this blog will know that I have a fair bit to say about birth-related language. Lots of aspects of this have captured my attention in the past, but among the things that I always notice are terms that are misogynistic, language that inappropriately blames women (or babies or fathers or families) and the use of judgemental words or phrases to name conditions or situations. As ever, I want to add the caveat that the development and use of such phrases is rarely down to individuals, and it is the paradigms and not the people whose value I am questioning.
Today’s example, which could be argued to fall into all of the categories that I have just mentioned, appears in a paper published in the British Journal of Obstetrics and Gynaecology, although it may well have been used elsewhere – that’s just the first time I noticed it. I was interested in DeFranco et al’s (2014) article because they seemed to be suggesting that having a longer interval between giving birth to one baby and becoming pregnant with the next (a span of time that is described in obstetric circles as the interpregnancy interval) was associated with better outcomes. I knew that this had long been thought to be the case with preterm birth (in that we have long known that a shorter interval between babies increases the chance of the baby being born preterm), but could IPI affect gestational length in other ways as well?
Enter Defranco et al (2014), whose study adds to our body of knowledge by showing that, in their data set, a shorter interpregnancy interval (or IPI) seemed to be correlated with shorter gestation in the later baby. This finding is fascinating, although in my understanding of the limitations of retrospective research which is carried out using the medical records of women who have previously given birth, the conclusion needs to be treated as an interesting one which warrants further research, rather than something ready to be carved in stone. There are also reasons to look closely at the statistical tests used in this research, and several other researchers have concerns about which women were included, especially as we know that there is considerable variability in normal pregnancy length between women who have different demographic and personal characteristics, for instance ethnic origin and height.
So I was quite surprised – and yes, a bit dismayed – when I noticed that these researchers had used the term inadequate interpregnancy interval in their paper.
Do we really have enough evidence at this stage to define a span of time between pregnancies as ‘inadequate’? I don’t think we do, for the reasons above, and others. But even if we did have enough evidence to say that an interpregnancy interval of less than a certain amount of time is associated with an overall increase in the chance of problems, then who are we – as professionals and researchers – to use a word or phrase which carries such a value judgement?
I was reassured to discover that I was not alone in my concerns about this paper. BJOG Emeritus Editor Philip Steer wrote a response to it which has just been published in the print journal. He has also questioned the use of certain statistical tests and the definition of ‘short interpregnancy interval’, pointing out that we already know that there are racial differences in gestational length, and that some of the women who DeFranco et al (2014) are defining as having an inadequate interpregnancy interval may actually be having physiologically normal pregnancies that are of the right length for them. And I know that others are questioning this, and may be writing on this issue as well, so I look forward to reading their thoughts.
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DeFranco EA, Ehrlich S and Muglia LJ (2014). Influence of interpregnancy interval on birth timing. BJOG: An International Journal of Obstetrics & Gynaecology 121(13): 1633-40.
Setting: Ohio, USA.
Study Population: Singleton, non-anomalous live births ≥20 weeks to multiparous mothers, 2006–2011.
Methods: Birth frequency at each gestational week was compared following short IPIs of <6, 6–12 and 12–18 months versus referent group, normal IPI ≥18 months.
Main outcome measures: Frequency of birth at each gestational week; preterm <37 weeks; <39 and ≥40 weeks.
Results: Of 454 716 births, 87% followed a normal IPI ≥18 months, 10.7% had IPI 12–18 months and 2.2% with IPI <12 months. The risk of delivery <39 weeks was higher following short IPI <12 months, adjOR (odds ratio) 2.78 (95% CI 2.64, 2.93). 53.3% of women delivered before the 39th week after IPI <12 months compared with 37.5% of women with normal IPI, P < 0.001. Likewise, birth at ≥40 weeks was decreased (16.9%) following short IPI <12 months compared to normal IPI, 23.2%, adjOR 0.67 (95% CI 0.64, 0.71). This resulted in a shift of the frequency distribution curve of birth by week of gestation to the left for pregnancies following a short IPI <12 months and 12–18 months compared to, birth spacing ≥18 months.
Conclusions: While short IPI is a known risk factor for preterm birth, our data show that inadequate birth spacing is associated with decreased gestational age for all births. Pregnancies following short IPIs have a higher frequency of birth at all weeks of gestation prior to 39 and fewer births ≥40 weeks, resulting in overall shortened pregnancy duration.