A paper has been published online in the British medical journal today
suggesting that survival of extremely premature infants (less than 24
weeks gestation) has not improved in the last decade. This comes less
than a week before a debate in the House of Commons on the Human
Fertilisation and Embryo Authority bill. It has been claimed that this
paper “completely blows out of the water” the arguments of
anti-abortion MPs who hope next week to push for a reduction in the
cut-off for legal abortion (currently 24 weeks).
The debate in the UK on changes to abortion law has drawn heavily on conflicting studies about the viability of extremely premature infants. One specialist neonatologist provided evidence last year to the Commons committee on science and technology that survival rates for extremely premature infants had improved. He was heavily criticised at the time for using unpublished, non-peer reviewed data, though this data has subsequently been published in a peer-reviewed journal. He argued that as many as 50% of infants at 22 or 23 weeks gestation who are admitted to his large London newborn intensive care survive to be discharged from hospital.
In contrast today’s paper in the BMJ points out that of all 22 week infants born alive in Trent, none survived, while less than 10% of 23 week infants survived. This figure is close to that provided in a national study of premature infant survival from the mid 90s (the EPICure study)
There are a number of reasons why these two studies have such widely different figures on the survival of extremely premature infants. Firstly, and most importantly, the survival of very premature infants is dependent upon a decision by doctors and parents to attempt to save their lives. In many parts of the world it is not felt to be a good idea to attempt to resuscitate extremely premature infants. Not surprisingly, the survival rates for such infants in those places are very low. The higher survival rate from the London hospital is likely to reflect at least in part a more pro-active approach to the management of extremely premature infants. Attitudes about the likelihood and value of survival affect both the resuscitation of extremely premature infants in the delivery room as well as their subsequent course in intensive care.
Secondly, the population of extremely premature infants varies in how sick they are. Some infants are so fragile that they do not survive labour. Others, by virtue of their genetics, the course of their development, or medical decisions, are relatively stronger and more likely to survive. The Trent study looks at all extremely premature infants born alive in a region of 4.6 million people. The London study includes infants born in a specialised academic maternity hospital as well as a small number of extremely premature infants transferred in from elsewhere. There are good reasons to think that the survival rates in these two groups would be different.
Thirdly, the facilities for looking after extremely premature infants differ widely between the two studies. There are 16 hospitals in the Trent region that provide maternity and newborn services. Some of those hospitals would have little experience or expertise in looking after the smallest, most premature infants. Infants born in such units would have a much higher chance of complications and of dying than infants born in a hospital with a large specialised newborn intensive care unit. They may also need to be transferred to another hospital, a process that is highly risky for such infants.
What the BMJ paper shows is that in a large (and presumably reasonably representative) region of the UK, only a small proportion of newborn infants less than 24 weeks survive. Yet it is questionable how relevant this figure is to the argument about viability. If viability is relevant to the abortion debate it cannot be in terms simply of how many infants do survive. If that were the case, countries that do not resuscitate or provide intensive care to premature infants at higher gestational ages (for example 25 or 26 weeks) would be justified in allowing abortion up to a that later stage. Or countries that do not have newborn intensive care facilities, and hence cannot keep alive infants before 30 weeks or 32 weeks, could justify abortion up to that time. Yet that is not something that either the anti-abortion campaigners or those who defend the current cut-off would accept.
The claim about viability is not about whether or not premature infants at 21 or 22 or 23 weeks do survive, it is about whether they can survive, (if all medical care were available, and the doctors tried hard to keep them alive). The London study tells us more about that. It suggests that a proportion of premature infants even at 22 weeks can survive. However because of selection bias it cannot tell us what proportion of all fetuses at this gestation could survive (if all care were provided etc).
However the more important question is what we do with the information available. The facts (such as they are) about viability of extremely premature infants do not settle the normative question of whether abortion should be permitted at a gestation when some, most or many infants are viable. For that we need to determine why viability matters. The debate about the facts and the research studies obscures the important ethical question.
Links
New research on baby survival rates stokes abortion limit row Guardian 9/5/8
Premature baby study stokes row on abortion Times Online 9/5/8
Survival of extremely premature babies in a geographically defined population: prospective cohort study of 1994-9 compared with 2000-5 BMJ 2008
Survival and neurodevelopmental morbidity at 1 year of age following extremely preterm delivery over a 20-year period: a single centre cohort study Acta Paediatrica 2008
Some numbers in the abortion debate just can’t be relied on Bad Science Guardian 27 October 2007