Nadine Dorries makes an attempt to look at the evidence. She fails. [updated]

Nadine Dorries seems to have realised that simply dismissing as 'desperate tosh' a study in the British Medical Journal won't cut the mustard. The study looked at survival rates of premature babies in the Trent region of the UK, concluding that survival rates for births before 24 weeks had not increased since 1994-9. This undermines the argument that those survival rates are increasing, and the time limit for abortion should be brought down to 20 weeks from the current 24 weeks. Dorries has now at least attempted to address the evidence, on the 20 weeks campaign website. This is a marked improvement, but I think her effort still falls somewhat short.

First, some nonsense. Dorries writes:

"We were somewhat surprised to see that the article was not in this week's paper edition of the BMJ which many doctors did not receive until Saturday. Why then rush to get it onto the web and into the public domain? The BMJ editorial said that upper time limits were to be debated in the House of Commons 'this year'. What it didn't say is that they are actually to be debated and voted on in just ten days, on 20 May. So the rush to get this into the public domain was to influence that debate".

If you can't use the latest research to 'influence debate', then what is it for? Apart from that, it is perfectly normal for research articles to appear on journal websites some time before they appear in print. That is precisely so that articles can reach the public domain once they are ready for publication, without having to wait on production schedules.

What of the science, indeed. Dorries says that "the Trent study looks at results from 16 hospitals and has been running for years. It is not new and other studies have been published based on more recent data". She also claims that the results from Trent "have always been poor and well below those seen in top neonatal centres worldwide". As evidence for this, she cites a study from the University College London Hospital (UCLH). This study is a single centre cohort study comparing survival rates in the years 1981-85, 1986-90, 1991-95, and 1996-2000. [The first thing to note here is that the Trent study uses data up to 2005. So it is actually using much more recent data than the UCLH study.] The UCLH study found that "There was a progressive increase in survival at all gestational ages over the 20-year period".

This seems to be a classic case of how you have to be careful with research. The first thing to note is that the number of babies in the UCLH study is small. The total number of babies in the study was 12 for those born at 22 weeks gestation, and 56 for those born at 23 weeks gestation, over 20 years. This compares with 261 born at 22 weeks and 370 at 23 weeks, over 10 years, for the Trent study. The Trent study is likely to give more robust numbers. Dorries, on the other hand, writes that the UCLH study "showed no survivors at 22 or 23 weeks in 1981-85 but 71% (5/7) and 47% (8/17) respectively in 1996-2000". Note the tiny sample size this statement is based on. In the UCLH study, the authors don't give percentage survival rates for births at 22 weeks, because the sample sizes are simply too small to draw any conclusions. There is something odd about the admission figures here too. For births at 22 weeks gestation, there was 1 admission in 1981-85, 3 in 1986-90, 1 in 1991-95, and 7 in 1996-2000. The comparable figures for births at 23 weeks are 7, 23, 9 and 17. There are very large variations here that suggest that the different time periods may not be directly comparable.

Perhaps the most serious problem with comparing the Trent and UCLH studies, though, is that they don't appear to be measuring the same things. In the Trent study, the authors write "We included in the study infants alive at the onset of labour". In contrast, the UCLH authors write "All infants born between 22 and 25⁺⁶ weeks of gestation between 1981 and 2000, who were admitted to the tertiary neonatal intensive care unit of UCLH (UK), within 1 week of birth, were enrolled into our study. In addition, the UCLH labour records for the years 1991–2000 were scrutinised to identify all infants who were born alive between 22 and 25⁺⁶ weeks of gestation, but who died in the delivery room". Hence the Trent study includes still-births as deaths, but the UCLH study does not. According to the Trent study, of births at 22 weeks, 43% were stillborn in 1994-99, and 40% in 2000-5. Of births at 23 weeks, 28% were stillborn in 1994-99, and 20% in 2000-5. For the UCLH study we don't know what these rates are. The Ministry of Truth blog has noted an anomaly in that the UCLH study reports a massively lower proportion of deaths in the delivery room compared to the Trent study. So there is at least a possibility that the UCLH survival rates are inflated in comparison to the Trent study by selection bias: perhaps more infants are being admitted to neonatal intensive care in Trent than in UCLH.

It's also worth noting that the Trent study covered a whole area (the Trent health region in the UK), while the UCLH study covered a single hospital. As the authors of the UCLH study write, "Large population-based studies [such as the Trent study] have the advantage of avoiding problems of selection bias and enable the accumulation of large numbers to reduce statistical errors. However, they inevitably represent the outcome from a very heterogeneous range of perinatal facilities...It is therefore inevitable that these units encompassed a wide range of staffing, resources and expertise in the care of extremely preterm infants. In addition, it seems likely that the maternity units encompassed a range of management policies (both obstetric and paediatric) towards infants born at the limits of viability, ranging from ‘proactive’ to ‘noninterventionist’. Hence, it is not surprising that average survival figures obtained from large population based studies will be different from those observed from single centre cohorts". As the editorial in the BMJ that accompanies the Trent studies says, "Single centre studies are confounded by selection bias and tend to overestimate the likelihood of survival". In other words, to compare the Trent and UCLH studies in the way Dorries is trying to do, and draw the conclusion that survival rates in the Trent health region are 'poor', is not a sensible thing to do.

So Dorries has looked at the evidence, which is better than dismissing it as 'tosh'. However, she seems to be drawing erroneous conclusions from an inappropriate comparison of two different studies. By coincidence, this inappropriate comparison supports Dorrie's agenda. How convenient.