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Jim’s growth chart navigator

November 23, 2019

September’s series on fetal growth charts took 16 posts to show why customisation is usually a bad idea. Some readers found them hard to navigate. This may help.

1. A tongue-in-cheek scene-setting about why it would be silly to use special United States baby weight charts.  And how some US paediatricians do exactly that (click here).

2. Technical stuff about scanning & how to create unbiased growth charts (click here).

3. The difference between population (reference) charts, and standard (healthy) ones (click here).

4. Customisation is not always bad. The principles of when it is a good idea, & when not (click here).

5. The theory (click here), & 6. the practicality (click here) of customising by race or ethnicity.

7. Customising on maternal weight (click here), 8. height (click here) or 9. parity & fetal gender (click here).

10. A digression on estimated fetal weight (click here).

11. Intergrowth-21 standard charts (click here) & 12. WHO standard charts (click here).

13. The Intergrowth/WHO plagiarism controversy (click here).

14. GROW customised charts (click here). Why almost everything about them is wrong. The reason I got embroiled in this topic.

15. Empirical studies (click here).

16. Summary (click here).

17. Addendum for twins (click here).

Jim Thornton

Home birth again

November 20, 2019

Most people imagine hospital is the safest place to be born, and it is if your mother has obstructed labour, major bleeding, or eclampsia. But hospital also has dangers. Not just infection, and blood clots, but staff led astray by false positive tests, or intervening “to be on the safe side”. Hospitals can also harm.

Consider the low-risk woman, without problems so far, who’s lucky enough to live in a rich country with skilled midwives who can look after her and her baby at home, but transfer if necessary.  Could planning to birth at home be equally safe?  Randomised trials are impossible, and simply comparing women who birth in either place is hopelessly biased because the groups are so different. The best we can do is compare cohorts of women judged low-risk at the start of labour, by “planned” rather than “actual” place of birth.

Two recent studies have done just that. The first from Canada (click here) retrospectively identified women without a risk factor before the onset of labour, classified them into planned home, or planned hospital, and randomly matched 11,493 in each group by parity and by whether or not they had had a previous Caesarean; apparently the latter is not judged a contraindication to home birth in Canada. There is potential for bias in this sort of retrospective matching, but the authors did their best to avoid it. The risk of stillbirth, neonatal death or serious morbidity did not differ significantly by planned place of birth (relative risk [RR] 1.03, 95% confidence interval [CI] 0.68–1.55). These findings held true for both nulliparous (RR 1.04, 95% CI 0.62–1.73) and multiparous women (RR 1.0, 95% CI 0.49–2.1). There were also fewer interventions among planned home births.

Last week (click here) a similar analysis came from Australia. Again the authors did their retrospective best, identifying 8,212 planned home births among low-risk women, and comparing them with a much larger number of planned low-risk hospital births. There were only nine baby deaths in the planned home group, but this was a slightly higher rate than for the planned hospital group, RR 1.6 (0.65–3.7). When divided by parity the differences were more marked in primiparous women RR 2.1 (0.58–7.8) than multiparous women 1.3 (0.4–4.1). But as the confidence intervals show, all the differences could have occurred by chance.

If these were the only studies, few partisans from either side of the home birth debate would be convinced. They are too small for precise estimates and there’s too much scope for retrospective classification errors. But they’re not.

The 2011 UK Birthplace study (click here) included 17,000 low-risk women planning birth at home, and was much more rigorous. Classification of risk and planned place of birth was done prospectively, before labour started. This reduces bias. In Birthplace for low-risk women having a first baby, planned hospital birth was safer for the baby, 5.3 v 9.3/1000 adverse perinatal outcomes, despite nearly half transferring to hospital in labour.  For second or subsequent births, there was no difference in adverse baby outcomes, the transfer rate was only 10%, and home birth substantially reduced intervention.

A similar 2015 study from the Netherlands (click here) included 466,112 low-risk women who planned to have a home birth at the onset of labour and 276,958 who planned a hospital birth. For first births the RR of baby death was 0.94 (0.76–1.16) and for second and subsequent births 1.02 (0.78–1.33).

Taken together the data are reassuring for low-risk multiparous woman in a rich country like UK, Netherlands, Canada or Australia where midwives are registered and well trained. For anyone like me who’s worked in hospitals for 40 years and seen both wise and unwise interventions, these data are plausible. Planned home birth, with transfer to hospital if problems develop, is safe, and intervention rates are much lower. For first births the highest quality study from the UK, Birthplace, suggests hospital is a bit safer and transfer rates are rather high.

The NHS is right to offer all low-risk multiparous women a home birth.

Jim Thornton

Note. Before anyone asks, birth in a midwife-led unit, whether freestanding or alongside a consultant-led unit, is safe for low-risk mothers, whether having their first or subsequent births. But everyone knows that. It’s hardly controversial any more.

Refusing Down’s screening

November 11, 2019

A woman successfully sued the NHS last month for not diagnosing and aborting her Down’s fetus after she had apparently declined screening (Mordel v Royal Berkshire NHS Trust, click here or 2591).

Background

Women considering Down’s screening need to know what they are getting into. Screening only gives a risk. If it’s high a needle test will confirm the diagnosis, but may cause miscarriage of a normal fetus. And the “treatment” is abortion. If you don’t want that, steer clear.

Midwives and sonographers must ensure that everyone who wants screening gets it, but avoid normalising it, or offering it in such a way that women get pressured into acceptance. It’s easy for compliant, or confused women to get sucked passively in.

The facts

My summary. Numbers refer to the judgment paragraphs.

Mrs Mordel was offered Down’s screening by her midwife, Ms Foley, and “accepted” combined screening at 11-13 weeks. This meant adding a measurement of the thickness of the skin over the back of the neck (nuchal test) to the routine scan, and undergoing an additional blood test. She expressed doubt as to whether, if the screening showed a high risk, she would undergo the second phase needle test with its small risk of causing miscarriage [8].  The midwife booked the scan and nuchal test, and gave her the NHS Down’s screening leaflet, which Mrs Mordel decided not to read because she had watched a You Tube video and “understood the position” [36]. In cross-examination, she confirmed that she had a good command of English and was quite comfortable in dealing with medical professionals in English [31]. When she attended later for the scan the following exchange took place.

The sonographer, Ms Bracher, having introduced herself, asked “Do you want the screening for Down’s syndrome?” Mrs Mordel said “No”. Ms Bracher said, “So we are not doing the screening then, we are just doing the dating scan and I will be checking the baby and making sure that the dates are correct”. There was no response from the claimant. The claimant was asked to lie down on the table. Ms Bracher then clicked on the box in the dropdown menu, “Down’s screening declined”, and this was not a mistake – the claimant had said “no” and nothing else.”[55]

At the end of the scan the sonographer wrote “Down’s screening declined” on the report, a copy of which she filed in Ms Mordel’s hand held notes, and which Ms Mordel agreed that she had read [38]. The screening blood test which Ms Mordel should have been expecting was not done, and no screening result was ever issued. At later visits with her midwife no further discussion of Down’s screening took place. A Down’s affected baby was born.

The claim and the ruling

Mrs Mordel initially claimed that the sonographer had not said anything, but the judge rejected that, leaving her alternative claim that the counselling described above was inadequate. Five experts were divided and the judge couldn’t choose between them [134]. He considered the following factors.

There were language issues. Mrs Mordel was Polish[8] . Her “English is good but far from excellent” [21], although she was “happy to receive the NHS booklet in English rather than Polish” [23].

She was not the sharpest tool in the box, although he put it in judicial language. “There were occasional failures to understand what was being put to her by both counsel, particularly if the question or proposition had a degree of nuance or complexity. On reflection, and with respect to the claimant, I put that down not primarily to lack of competence in the English language (although it remains a significant factor) but to her general level of education and sophistication” [21].

She really wanted the test. This was an unplanned pregnancy [8], her mood was low [8]. She had no religious and ethical objection to abortion. Although a Roman Catholic, not that she described herself in that way, my sense of her evidence was that she was not particularly devout and in cross-examination she said that she attended Mass 3-4 times a year when she felt a need to. She has previously used contraception and has not married her partner [30].

And he believed her. He found her a guileless witness and therefore believed her statement soon after the birth, that she thought that having asked for testing, she had been tested. Much of his argument took the form that since she clearly had misunderstood, she must not have been adequately informed.

He ruled that Ms Bracher the sonographer should have questioned her harder [98, 99], and that “Midwife Foley failed to discharge her duty […] in not exploring why the combined test had not been carried out” [141]. At that later time point there would have been time for an alternative screening test.

Comment

Coo-er! It all sounds rather patronising – the staff should have triple-checked because she was a stupid foreign unmarried woman with an unplanned pregnancy who didn’t understand plain English! But I wasn’t in court. Nor probably were you dear reader. We can only comment on what we read.

But the judge revealed, in my opinion, a serious misapprehension, namely that non-directive counselling is easy. “The steps required to guard against parental choice not being respected are not onerous” [86].

Really? Yes, the sonographer could have pressed more. Yes the midwife could have asked why she’d changed her mind. But this is what we teach sonographers and midwives not to do.  Don’t question women’s decisions.  That is the way people get bullied into screening that they don’t really want.

To be fair the judge anticipated and rejected this criticism [90]. In his opinion that risk only arises in the event of maladroit or insensitive interrogation, and NHS professionals are well habituated to avoid that. He was careful not to argue that only women who decline screening should have their refusal double checked. Having established [51] that Ms Bracher would have spoken in the same way, to a woman who had changed her mind to undergo screening, he argued [95] that this would also have been inadequate because of the risk that patients who did not want screening for Down’s syndrome would end up having the nuchal test.

Midwives and sonographers have difficult jobs. Let’s hope they all do better. That they double check both those women who change their mind to decline, and those who shift to acceptance, and do it in such a sensitive way that no-one feels bullied into testing.

Let’s hope they don’t only double check vulnerable non-English speaking decliners, and that more widespread questioning doesn’t pressure more women into testing they don’t really want.

Jim Thornton

 

 

Standard, Population & Customised fetal size charts 17 – addendum for twins

September 29, 2019

Twins, especially identical ones,  tend to be smaller than singletons (click here). This has led to the suggestion that they should have special charts (click here, and here). The support group, the Twin and Multiple Birth Association, (TAMBA) apparently supports the idea (click here), but it’s a bad one.

The Perinatal Institute, normally an advocate of customisation,  explains why rather well (click here). To quote:

The [twin] charts […] are based on reference values derived from the whole population, not only from uncomplicated pregnancies. Therefore, they do not represent a normal growth standard but one that may have been affected by an unspecified number of pathological factors. This concept is particularly important in twin pregnancies as they have a substantially increased number of complications.”

“The pattern of slowed growth from 30-32 weeks in many (but not all) twin pregnancies may be pathological due to late onset fetal growth restriction associated with placental insufficiency,
which usually also becomes manifest from around 32 weeks. Adjusting the curves downwards may normalise pathology, reduce recognition of pregnancies at risk, and lead to false reassurance.”

Correct. Twin smallness is not healthy smallness. Twins also have higher rates of stillbirth, cerebral palsy and other problems. The reasons not to customise by ethnic group (click here), height (click here), weight (click here) and parity (click here), also apply to twin customisation. Special “small” charts for twins condemn them to being classified as “normal for twins”.

The Italian group (Ghi et al click here) recognise the problem; “adjusting for multiple pregnancy, thereby shifting the normal range of fetal growth downward, has the potential to mask truly growth restricted twins and increase perinatal morbidity from failure to recognize growth restriction”, but hope that because they excluded twins born before 36 weeks, or below the 5th centile on a singleton chart, that it will go away. They compare their twin chart with a local customised Italian one (click here) but provide no data of the detection rate of pathology.

The STORK study authors (here) compared detection rates for stillbirth, with a singleton chart. But their chosen comparison chart (Poon click here) which correctly excluded babies of smoking mothers, and those with major medical disease, has it’s own problems. Leona Poon not only based her chart on routinely collected data with all the error and bias that entails, but also used the weights of babies who were actually born, which seriously distorts the preterm part of the chart (click here).

Many twin fetuses fall below the Intergrowth-21 or WHO singleton growth standards. Some even below the 1st centile. These are reasons both to use charts with reasonably precise extreme centiles, and to consider delivery before term (click here).  Some experts also recommend basing decisions on estimated fetal weight discordance (EFW) a sign of selective growth restriction, is included as a factor in delivery timing. If so, it is preferable to use the most accurate and unbiased  Intergrowth-21 EFW formula (click here).

TAMBA should think again.

Jim Thornton

Standard, Population & Customised fetal size charts 16 – summary

September 21, 2019

That’s it folks. Let’s summarise.

Standard growth charts tell you how big a healthy fetus from a healthy pregnancy and healthy mother should be. Population charts plot the average for your local population, including unhealthy pregnancies (click here). Customised charts adjust the size on the basis of individual parental features (click here).

Customisation improves detection of pathology if we can be sure that the feature customised on, is not only objective and reproducible, but also not associated with pathology (click here).  Customisation on factors associated with pathology, such as smoking, condemn the small sick fetus damaged by smoking, to being classified as “normal for smoking”. Fortunately no-one customises on maternal smoking.

But some people do customise on maternal ethnicity, weight, height and parity. Ethnicity is not objective (click here) and is associated with pathology (click here). Maternal weight is objective, but at both extremes is associated with pathology (click here). Maternal height is objective but also associated with pathology, albeit only at the lower end (click here). Parity is objective but also associated with pathology (click here).

Fetal sex is objective and negatively associated with pathology, with larger male fetuses having higher mortality (click here). This should make it an ideal factor on which to customise, and is the reason why, after birth, paediatricians routinely use separate charts for boys and girls. But it’s not suitable for routine prenatal use at present.

The main customised charts available in the UK are produced by The Perinatal Institute (click here). They provide customised charts for fundal height and for estimated fetal weight. Their training programmes for measuring fundal height are excellent, but the fetal weight estimates on which those charts are based use Hadlock’s outdated formulae. Their customisation formulae for both fundal height and fetal weight are secret. Their charts customise on maternal ethnicity, weight, height and parity, and are therefore likely to condemn the fetuses of first pregnancies and of mothers whose ethnicity, weight and height are markers of past and present deprivation, to having pathology missed.

Fetal growth charts should be created on large populations, using careful techniques to avoid bias (click here). Only the two standard charts created by Intergrowth-21 (click here) and by WHO (click here) have done this.  A well-publicised academic dispute (click here) between the Intergrowth-21 and WHO authors, involved accusations of plagiarism, but had nothing to with the science. Both charts are scientifically rigorous. However, the Intergrowth-21 sample was twice the size of WHO’s, and that group used slightly more advanced techniques for avoiding bias, so their chart is to be preferred.

Claims that the introduction of customised charts caused the recent fall in UK stillbirth rates do not bear close scrutiny (click here).

Suggestions that standard charts are flawed because they detect different rates of growth restriction or macrosomia in different populations make no sense; that is a feature of growth standards.

Empirical comparisons (click here) between customised and population charts are unhelpful because they compare two type of customised chart. All empirical studies suggesting that customised charts detect more pathology than standard charts have also reported higher false positive rates with customisation. No empirical study has ever shown greater detection rates of pathology for a fixed false positive rate. The best quality empirical study (the POP study from Cambridge), where results were also concealed from clinicians, showed no difference with customisation.

Population and customised charts, as currently available, cannot be recommended.

The Intergrowth-21 or WHO fetal growth standard charts should be used.

Jim Thornton

Standard, Population & Customised fetal size charts 15 – empirical studies

September 20, 2019

How do customised charts perform in practice?

Previous posts have described why, in theory, fetal growth standard charts such as Intergrowth-21 or WHO are preferable to local population or customised charts. Here we look at empirical comparisons. Unfortunately there are few good ones, many are misleading*, and reliable ones difficult to do.

Comparisons between customised and population charts (e.g. here, or here) don’t help; a population chart is simply a type of customised one. Claims that percentages of fetuses falling above and below various centiles vary more with standard charts than with customised ones (Francis et al 2018 click here) miss the point. This is a feature not a bug of standard charts!

Studies comparing the rate of detection of fetuses who are small for gestational age (SGA) by charts A and B, but which either don’t define SGA (Gardosi and Francis 2005 click here) or define it by a third chart C (e.g. Odibo et al. 2018 click here) confuse the issue as well.

We need to compare different chart’s detection rates for the sort of pathology that matters, stillbirth or brain damage, or for surrogates for those things, such as low cord pH, Apgar scores or admission to neonatal intensive care.  Such studies need to fix the false positive rate. Detecting more babies with adverse outcomes is not necessarily better if the false positive rate is also higher. Francis et al 2018 (click here) reported that customised charts would have detected 411 stillbirths compared with Intergrowth’s 229 in a cohort of 1.2 million term singleton pregnancies. However to do so, the customised charts would have classified 10.5% of pregnancies as growth restricted, while Intergrowth-21 would have only classified 4.4%. At least two other studies, (Anderson et al. 2016 click here) and (Pritchard et al. 2018 click here) suggesting that customised charts detect more pathology than Intergrowth-21, also had double the false positive rates with customisation.

A recent large retrospective US study (Kabiri 2019 click here) of five different charts, including Intergrowth-21, WHO and GROW, compared detection rates of a range of different adverse outcomes for a fixed 10% false posive rate (figure 2 in the paper). Intergrowth had the highest sensitivity overall, and GROW the lowest, albeit the differences were small and the confidence intervals overlapping. Another retrospective study from Scotland (click here), which also reported detection rates for fixed false positive rates, showed that partial customisation on two objective factors (maternal height and parity) did not improve detection of pathology.

With one exception, these studies are the best we have. However, such retrospective comparisons where one chart type was used in practice are tricky because clinicians will have acted on the result from the chart in use. If, for example, they induced labour early they may have prevented, or caused, an adverse outcome, so called treatment paradox. Caesarean for a suspected small baby may prevent the death which the chart was correctly predicting. Conversely induction for a false prediction of growth restriction may cause hypoxia in a previously healthy baby as a result of long labour.

This final problem is difficult to avoid. It requires scan findings to be concealed from clinicians. This has only been done once, in the POP study from Cambridge (click here), which showed that customising using the GROW software did not improve detection rates of any adverse outcomes.

And that’s pretty much it. Many other papers purport to show that customisation is good or bad, but they all either reported percentages above or below different centiles, or compared customised with population charts, or detection rates for pathology without fixing false positive rates, or all three, or came to no clear conclusion.

Next and finally, a summary of what we have learned (click here).

Jim Thornton

* Readers beware. Authors often use the terms population, standard and customised charts rather loosely.

Standard, Population & Customised fetal size charts 13 – The Intergrowth/WHO plagiarism controversy

September 18, 2019

Soon after the Intergrowth-21 charts were published, allegations of skullduggery appeared from WHO (click here). Rumours flew around, big money was involved, and the organisations employing each group of researchers, WHO and Oxford University, conducted enquiries. Eventually WHO referred Jose Villar and Stephen Kennedy, two of the leaders of the Intergrowth-21 group, to the UK General Medical Council (click here), who declined to investigate.

Supporters of WHO claimed that the two Intergrowth-21 authors had plagiarised a previous WHO protocol. Villar had been employed by WHO before he moved to Oxford, and Kennedy had been a member of a WHO expert group.

Defenders of Intergrowth-21 say that the idea of creating fetal growth standards was not only “obvious”, but had already been widely discussed in public long before either team set to work.

The full story has never been published, but the editor of the Lancet, who had seen both the WHO and Oxford reports, sided with the Intergrowth-21 group and concluded that at worst it was a matter of academic rivalry (click here).  His comment that the WHO enquiry was “disappointingly insubstantial” clearly stung WHO, who responded by publishing it here, the “report from reviewers”.  Judge for yourself. The WHO also took the opportunity to confirm that.

“WHO has never questioned the scientific validity of the research conducted and the papers produced by Oxford University (as published in the Lancet and other peer-reviewed journals)”.

Three supporters of the WHO allegations wrote a letter which added little (click here). The Oxford report, exonerating the Intergrowth-21 authors, remains unpublished. And there the matter rests.

The issue is long past. But it’s worth recalling, because advocates of alternatives occasionally allow the idea to get out that “There’s something fishy about the Intergrowth or WHO charts”. There is not. The allegations never included any scientific criticism of either. Rather the opposite. The idea of international fetal growth standards was so good, that academic rivals sought credit for it. This mattered once to the people involved, but not to the rest of us.

Next customised charts (click here).

Jim Thornton

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