Abortion time limits
A briefing paper from the BMA
May 2005
Part two - Factors influencing views on abortion time limits
Fetal viability
During Parliamentary debate on the Human Fertilisation and Embryology Bill in the late 1980s considerable emphasis was placed on the gestational age at which a fetus was considered viable in deciding where the time limits should be set. This is the basis on which the 24 week limit was included in the current legislation. One of the arguments for reviewing the time limits for abortion is the belief that due to advances in medical technology fetuses are now viable before 24 weeks’ gestation. There have certainly been major developments in the care of preterm infants and the use of antenatal corticosteroids, mechanical ventilation and exogenous surfactant replacement have been cited as a few of the major medical advances that have improved clinical outcomes for preterm infants. [Go to reference 33]. The extent to which these advances have significantly changed our understanding of the gestational age of fetal viability, however, depends to a considerable extent on how “viability” is defined; whether, for example, it is understood to mean simply that the fetus is capable of being born alive or, at the other extreme, that it is capable of surviving through childhood with no or minimal disabilities, or whether some other definition of 'viability' is used.
Although it is helpful to pinpoint a particular gestational age as being the point of viability, it is important also to bear in mind that gestational age is not the only factor that affects the possibility of a fetus being considered viable (however that is defined). Factors such as birth weight, whether it is a multiple pregnancy and the gender of the fetus also affect the likely outcome. [Go to reference 34]. Even if a fetus reaches a gestational age which is considered the minimum possible for viability, many others factors come into play as to whether that particular fetus is or may be viable. Another relevant factor to consider in discussing viability therefore is whether 'fetal viability' relates to the minimum stage possible for any fetus to survive or, for example, the stage at which the majority of infants will survive. Defining the gestational age of “fetal viability”, therefore, is by no means straightforward.
What is meant by 'viability'?
The term “viability” is subject to different interpretations. For some people it is considered to be synonymous with being 'born alive', irrespective of the length of time the baby survives or the extent and nature of any medical problems or disabilities. Using this definition of viability, an anencephalic newborn who lacks all or most of the cerebral hemispheres, but is capable of using its lungs, would be considered viable. This was the view taken by Mr Justice Brooke in the 1991 legal case of Rance v Mid-Downs HA [Go to reference 35] in which he stated “The primary dictionary meaning of the word 'viable', which is derived from the French word 'vie', is 'capable of living'… In my judgment the word 'viable' was simply being used [by Parliament] as a convenient shorthand for the words 'capable of being born alive'.'
Other legal cases, however, have suggested that viability does not equate solely with being born alive. For example, in a case before the English courts in 1988 [Go to reference 36] and the earlier American case of Roe v Wade [Go to reference 37] the notion of being capable of 'meaningful life' is introduced. In the Roe v Wade judgment it was said:
'With respect to the State’s important and legitimate interest in potential life, the 'compelling' point is at viability. This is so because the foetus then presumably has the capability of meaningful life outside the mother’s womb' (emphasis added).
There was no expansion on the concept of “meaningful life” in these or subsequent legal cases but it might be argued that it requires, as a minimum, a reasonable period of survival.
How is gestational age calculated?
A further difficulty with pinpointing the gestational age at which fetuses are considered viable relates to variations in the way in which gestational age is calculated. Gestational age has traditionally been calculated, for medical purposes, from the date of the start of the woman’s last menstrual period which is notoriously unreliable. The National Institute for Clinical Excellence now recommends that gestational age should be calculated by measuring the crown-rump length during the 10-13 week ultrasound scan. [Go to reference 38]. This should lead to greater consistency and accuracy in the timings used for medical purposes.
In law, however, there remains a modicum of uncertainty as to how the 24 week limit in the Abortion Act should be calculated. Kennedy and Grubb, [Go to reference 39] for example, outline four possible dates from which the 24 weeks’ gestation could be calculated:
(A) the first day of the woman’s last period;
(B) the date of conception;
(C) the date of implantation;
(D) the first day of the woman’s first missed period.
It is also important to ensure that women understand how gestational age is calculated so that those who wish to access abortion services can do so within the time limit.
Professional guidance
Given that the survival of preterm infants is dependent, to a considerable extent, on the technological skills that are available, it is not surprising that notions of viability can be determined by geographical location. This is acknowledged by the World Health Organization which, in its 1998 guidance on resuscitation of newborn infants, says 'Viability of the newborn in terms of gestational age may differ according to local circumstances.' It goes on to say, however, that 'even with the best resources available, the rate of survival of newborns below 26 weeks of gestational age or 1000 g is low.' [Go to reference 40]
In the UK, past professional guidance referred to a viability cut-off point of 24 weeks. This was the limit recommended by the Royal College of Obstetricians and Gynaecologists (RCOG) in the late 1980s which was quoted during debate on the 1990 Act. [Go to reference 41]. In 1997, the Scottish Executive Committee of the Royal College of Obstetricians and Gynaecologists restated this view when discussing the benefits of antenatal corticosteroid administration, stating:
'The proposed lower limit of 24 weeks is based on the accepted lower limit of viability, and the upper limit of 34 weeks is an arbitrary limit beyond which cost-effectiveness is questionable.' [Go to reference 42].
| Gestation (weeks) | Survival to discharge (%) |
| 21 | 0 |
| 22 | 1 |
| 23 | 11 |
| 24 | 26 |
| 25 | 44 |
It is important to recognise that even though some babies have survived at a very early stage, the threshold of viability cannot be continually pushed back since there is a limit beyond which the lungs will simply be insufficiently developed to sustain life. While embryonic lungs start to form as early as four weeks into a pregnancy, their final maturation is continuing right up to the end of a normal pregnancy.
Research evidence on survival following preterm delivery
Data on viability, and particularly information that can be transferable to other units, can be difficult to obtain. This is because babies delivered at low gestations may not survive labour or past the delivery room, the data set can be small and many figures are obtained from single units where there may be different policies and medical resources available that will impact on the results obtained.
The EPICure study
One of the most comprehensive and significant population studies currently underway that looks at viability is the EPICure study which featured on the Panorama programme – Miracle baby grows up. [Go to reference 44]. The study looked at the survival [Go to reference 45] and later health status at 2½ [Go to reference 46] and 6 [Go to reference 47] years old of children born at 25 weeks or less gestation over a 10 month period in 1995 in the United Kingdom and Ireland.
Further details on the study, for example the paediatric and psychological assessment methods and measurements used, can be found on the EPICure study website at www.nottingham.ac.uk/human-development/EPICure - go to the website here.
The outcomes of the study relevant to this paper can be summarised as follows:
| Summary of outcomes among extremely preterm children [Go to reference 48] | ||||
| Outcome | 22 wk | 23 wk | 24 wk | 25wk |
| Number (per cent) | ||||
| Died in delivery room | 116 (84) | 110 (46) | 84 (22) | 67(16) |
| Admitted for intensive care | 22 (16) | 131 (54) | 298 (78) | 357(84) |
| Died in Neonatal Intensive Care Unit | 20 (14) | 105 (44) | 198 (52) | 171(40) |
| Survived to discharge | 2 (1) | 26 (11) | 100 (26) | 186(44) |
| Deaths post-discharge | 0 | 1 (0.4) | 2 (0.5) | 3(0.7) |
| Lost to follow-up | 0 | 3 (1) | 25 (7) | 39(9) |
| At 6 years of age: | ||||
| Survived with severe disability | 1 (0.7) | 5 (2) | 21 (5) | 26(6) |
| Survived with moderate disability | 0 | 9 (4) | 16 (4) | 32(8) |
| Survived with mild disability | 1 (0.7) | 5 (2) | 26 (7) | 51(12) |
| Survived with no impairment | 0 | 3 (1) | 10 (3) | 35 (8) |
The EPICure study defined degrees of disability as follows:
- Severe disability - 'if it was considered likely to make the child highly dependent on caregivers and if it included nonambulant cerebral palsy, and IQ score more than 3 SD below the mean, profound sensorineural hearing loss, or blindness'
- Moderate disability – 'if reasonable independence was likely to be reached and if it included ambulant cerebral palsy, and IQ score 2 to 3 SD below the mean, sensorineural hearing loss that was corrected with a hearing aid, and impaired vision without blindness'
- Mild disability – 'included neurological signs with minimal functional consequences or other impairment such as squints or refractive errors' [Go to reference 49]
Key points arising from the EPICure study
In relation to births up to 24 weeks’ gestation:
- Of the 761 live births up to 24 weeks’ gestation: 41% died in the delivery room, 42% died in the neonatal intensive care unit; and of the 128 (17%) that survived to discharge, 2% subsequently died.
- Of the 97 children born up to 24 weeks’ gestation who survived to discharge and were assessed at 6 years old: 28% had severe disability, 26% had moderate disability, 33% had mild disability and 13% survived without impairment.
In relation to births up to 23 weeks’ gestation:
- Of the 379 live births up to 23 weeks’ gestation: 60% died in the delivery room, 33% died in the neonatal intensive care unit; and of the 28 (7%) that survived to discharge, 1 subsequently died.
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Of the 24 children born up to 23 weeks’ gestation who survived to discharge and were assessed at 6 years old: 25% had severe disability, 38% had moderate disability, 25% had mild disability and 12% survived without impairment.
In relation to births at 22 weeks:
- Of the 138 live births at 22 weeks’ gestation, 84% died in the delivery room, 14% died in the neonatal intensive care unit and 2 survived to discharge (1%).
- Of the 2 children born at 22 weeks’ gestation who survived to discharge, 1 had severe disability and 1 had mild disability at 6 years of age.
Trent health region study
The original survival data in the EPICure study were obtained in 1995. It is therefore helpful to look at more recent data on survival rates which are available from studies such as the regional Trent health study. This study looked at all European and Asian live births, stillbirths, and late fetal losses from 22 to 32 weeks’ gestation, excluding those with major congenital malformations. The original study considered live births, stillbirths and late fetal losses in women resident in the Trent health region between 1 January 1994 and 31 December 1997. [Go to reference 50]
The data were updated for the 4,112 births at 22-32 weeks’ gestation that took place between 1 January 1998 and 31 December 2001. [Go to reference 51] Among this latter group, although survival rates varied depending upon birth weight, the overall probability of survival to discharge home was as follows:
| 22 weeks | 23 weeks | 24 weeks | 25 weeks | |
| European births | 7% | 15% | 29% | 47% |
| Asian births | 3% | 11% | 27% | 51% |
Although the number of births at 22-25 weeks is likely to be small, the methodology used for the study included making adjustments to take account of this fact in order to derive more accurate estimates of survival.
It is important to recognise that this study looked only at survival rates to discharge and did not provide data on any degree of disability (mild, moderate or severe) in the children who survived, which was an important part of the EPICure study. It also excluded from the data any cases with major congenital malformations.