Memorandum 37
Submission from Professor John S Wyatt,
University College London
This submission is intended to address the following
questions:
(a) Does induced abortion lead to an increased
risk of preterm delivery in subsequent pregnancies?
(b) Have there been
significant improvements in the chances of survival for extremely
premature infants since the amendment of the Abortion Act in 1990?
EXECUTIVE SUMMARY
— There is strong, robust and widely
accepted scientific evidence that induced abortion leads to an
increased risk of premature birth in subsequent pregnancies.
— The increased risk of a preterm delivery
is between 1.3 and 2.0 and rises with the number of abortions.
— It is estimated that abortion in
the UK leads to approximately 400 additional very premature births
each year, of which around half are extremely preterm (less than
28 weeks). This will result in at least 40 additional neonatal
deaths per year.
— The consequential costs of the additional
premature births in the UK together with the risks of long-term
disability may be between 30 and 60 million pounds per year.
— Health professionals and abortion
providers have a duty to ensure that women and their partners
are informed of the potential risk that abortion carries for subsequent
pregnancies.
— There have been substantial advances
in the care of extremely premature babies born at the limits of
viability, since the Abortion Act was amended in 1990.
— A significant proportion of babies
born at 23 and 24 weeks gestation and cared for at major centres,
are now surviving, and it is likely that survival figures will
continue gradually to improve over the next decade.
INTRODUCTION
1. I am Professor of Neonatal Paediatrics at
University College London and Honorary Consultant Neonatologist
at University College London Hospitals Foundation NHS Trust. My
area of expertise is the intensive medical care of newborn infants
and the causation and consequences of brain injury in the newborn.
I have been a Consultant Neonatologist at a major regional referral
centre since 1988. I am a member of an internationally-recognised
multidisciplinary research group at University College London,
investigating the mechanisms, consequences and prevention of brain
injury in newborn babies. My qualifications are BSc, MBBS, FRCP,
FRCPCH, DCH.
Does induced abortion lead to an increased risk
of preterm delivery in subsequent pregnancies?
2. A highly significant number of reputable
scientific studies investigating the association between induced
abortion and increased risk of preterm delivery have been published
in peer-reviewed journals. In January 2003, Thorp and colleagues
published a detailed review of the available scientific evidence.
They analyzed results for 24 published studies of the effect of
induced abortion on the risk of preterm birth in subsequent pregnancies.1
The authors reported that 12 of the studies found a positive association
with increased risk ratios which were consistently between 1.3
and 2.0. Seven published studies found a dose-response effect,
in that the risk estimate increased with increasing numbers of
induced abortions. Each of three large cohort studies performed
in the 1990s showed an increased risk of preterm delivery and
a dose-response effect. These studies had attempted to avoid recall
bias by obtaining data on induced abortions from prospectively
obtained records rather than self-reporting. .
3. Another detailed review of the scientific
literature by Rooney and Calhoun,2 published in 2003, concluded
that at least 49 studies had demonstrated a statistically significant
increased risk of premature birth or low birth weight following
an induced abortion. Again the majority of studies showed a dose
-response relationship, and the greatest increased risk involved
extremely preterm infants below 28 weeks of gestation. It is striking
that only 8 studies failed to show an increased risk of preterm
delivery and no published studies demonstrated a protective effect
of previous induced abortion. The magnitude of the increased risk
with 2 or more previous abortions was substantially greater than
that associated with maternal age, marital status, parity or socioeconomic
status. Hence the authors argued that it was most implausible
that the statistical association could be explained by confounding
socioeconomic factors.
4. In 2005 Moreau and colleagues published a
detailed report based on data from the EPIPAGE study,3 a very
large and well-validated study of very preterm infants, performed
in France. Information was collected from all maternity wards
in 9 French regions in 1997. Data on previous induced abortions
were taken from hospital records in order to reduce recall bias.
The study was population-defined to exclude selection bias. The
authors tested the prior hypothesis that induced abortion would
increase the risk of subsequent very preterm birth due to infectious
or mechanical processes, but not the risk of very preterm delivery
due to vascular causes, especially hypertension.
5. Using a case control methodology three groups
of infants were enrolled;1843 very preterm live infants born at
less than 33 weeks gestation, 276 infants born at 33 to 34 weeks
of gestation and 618 unmatched full-term control infants born
at 39 to 40 weeks. The authors concluded that a history of induced
abortion correlated with an increased risk of very preterm birth
(adjusted odds ratio, 1.6; 95% confidence interval 1.2-2.1). Where
there was a history of more than 1 previous induced abortion,
the adjusted odds ratio was 2.9 (95% confidence intervals 1.3-6.5)
Controlling for maternal characteristics such as age, education
and history of smoking, had very little effect on the magnitude
of the increased risk. The association was unchanged if women
with previous preterm delivery were excluded. This study found
that there was no relationship between induced abortion and subsequent
preterm delivery resulting from pre-eclampsia. There were however
significantly increased risks for preterm delivery resulting from
antepartum haemorrhage, isolated fetal growth restriction, premature
rupture of membranes and spontaneous onset of labour. The risk
of preterm delivery associated with induced abortions tended to
be higher for extremely preterm deliveries between 22 and 27 weeks
of gestation (odds ratio 1.7) compared with delivery at 28—34
weeks of gestation (OR 1.4). A statistical association between
previous induced abortion and very preterm delivery in the presence
of fetal growth restriction was apparent in infants born at 28
to 32 weeks gestation.
6. The authors concluded that their findings
could not be explained as the consequence of methodological biases
or the effect of confounders. Their findings were consistent with
other recent studies that gave adjusted odds ratios between 1.3
and 2. They concluded that a history of induced abortion increases
the risk of very preterm birth, particularly extremely preterm
deliveries.
7. In another recent study, Ancel and colleagues
analysed data from ten European countries (the EUROP survey).4
A total of 2,938 preterm births and 4,781 controls at term were
included. Data were obtained from European countries with widely
varying rates of induced abortion. The authors concluded that
previous induced abortion was significantly associated with preterm
delivery and the risk increased with the numbers of abortions.
The adjusted odds ratios varied between 1.2 and 1.8. The statistical
association did not significantly vary between countries with
high and low rates of induced abortion. As with the French study
reported by Moreau et al, the extent of the statistical association
varied according to the cause of the preterm delivery. Delivery
due to spontaneous onset of preterm labour, premature rupture
of membranes and antepartum haemorrhage were all positively associated
with induced abortion, whereas delivery due to maternal hypertension
was not associated. The strength of the association between induced
abortion and premature delivery increased with decreasing gestational
age.
8. The mechanisms underlying this association
have not been elucidated. However it is striking that there is
a consistent relationship between abortion and preterm delivery
related to infectious and mechanical factors but no relationship
with delivery due to maternal hypertension or vascular abnormalities.
There is considerable evidence that induced abortion increases
the risk of infectious complications in a later pregnancy.5 This
may result from the revival of latent local infectious processes
caused by surgery at the time of the abortion or may be related
to mechanical factors leading to ineffective cervical closure
with an increased risk of ascending genital tract infections.
Cervical instrumentation has also been suggested to increase the
risk of endometrial damage, thus impairing trophoblastic invasion
and migration. This would increase the risk of placenta praevia
which is a major cause of antepartum haemorrhage, leading to preterm
delivery.
9. In conclusion, the scientific evidence of
a causal link between previous induced abortion and increased
risk of preterm delivery appears to be remarkably robust and consistent.
The effect is consistent across many different countries with
widely differing socioeconomic backgrounds and widely differing
attitudes towards induced abortion. The effect is also consistent
between studies published over a 50 year period from the 1960's
until 2005 and with a wide variety of study methodologies. The
effect is biologically plausible in that there is a consistent
dose-response relationship and a consistent positive relationship
between abortion and preterm delivery related to infectious and
mechanical factors but no relationship with delivery due to maternal
hypertension or vascular abnormalities. .
10. Extremely preterm delivery is associated
with a high risk of death in the neonatal period and with a greatly
increased risk of brain damage. Sadly, preterm delivery due to
infectious or haemorrhagic causes are particularly associated
with brain injury, leading to a substantially increased risk of
permanent disability including cerebral palsy, severe learning
difficulties and sensory impairment. 6,7,8 Hence there is substantial
evidence that induced abortion will result in death in a significant
number of infants born extremely preterm, as well as to a significantly
increased risk of subsequent children surviving with permanent
disability.
11. Approximately 5% of all infants are born
before 37 weeks of gestation in England and Wales, (equivalent
to about 33,500 per year) and approximately 1.4% are born at less
than 33 weeks (equivalent to about 9,400 per year). About 0.4%
or about 2,700 per year are born at less than 28 weeks. Approximately
50% of all abortions in England and Wales are undertaken in women
under the age of 25 years, whereas 75% of all livebirths occur
at a maternal age above 25 years (UK birth statistics).9 Thus
the majority of women who are considering abortion will subsequently
deliver one or more live children.
12. On the basis of published data, approximately
14% of all women in UK who deliver have had a previous induced
abortion. 10 Using this figure, and a relative risk of 1.3 gives
an attributable risk of approximately 400 additional preterm infants
born in the UK at less than 33 weeks per year. In extremely preterm
infants a higher relative risk of 1.6 gives an attributable risk
of about 230 additional infants per year born at less than 28
weeks.
13. Each additional extremely preterm infant
will have substantial acute care costs to the NHS of approximately
£30,000-100,000. In addition there is, unfortunately, a 15-20%
chance of substantial long-term disability in these infants, leading
to lifetime costs to society which may approach £1 million
or more for each child (costs estimated from current NHS negligence
claims). In addition, with an overall mortality of at least 20%,
it is likely that at least 40 additional premature infants will
die in the neonatal period each year.
14. Hence it can be concluded, on conservative
estimates, that the consequential costs to society from preterm
delivery associated with induced abortion amount to very approximately
£30-60 million per year.
15. Health professionals and abortion providers
have a duty to ensure that women and their partners are informed
of the potential risk that abortion carries for subsequent pregnancies.
(b) Have there been significant improvements
in the chances of survival for extremely premature infants since
the amendment of the Abortion Act in 1990?
16. Although mortality and morbidity remains
relatively high, there is consistent evidence of a steady improvement
in survival year-on-year for extremely preterm infants born at
24 weeks gestation or less. In 1995 the EPICURE study undertaken
in the entire of UK and Ireland showed that average survival to
discharge across the UK was 26% of live births at 24 weeks and
11% at 23 weeks. 11 In 2004 Hoekstra and colleagues12 published
detailed outcome data for a cohort of infants born between 23
and 26 weeks of gestation at a single tertiary neonatal centre
in Minneapolis, USA, over a 15 year period (Hoekstra et al. 2004).
These data show a consistent year-on-year improvement in survival
and for the period 1996-2000 there was an overall survival rate
following admission to NICU of 66% at 23 weeks of gestation and
81% at 24 weeks of gestation. Similarly Doyle and colleagues,
13 in a study of extremely premature babies delivered in the State
of Victoria in Australia found increased survival from 1991 to
1197 with recent data providing an overall survival rate of 41%
at both 23 and 24 weeks of gestation. Data from a prospectively-defined
long-term follow-up study at the Neonatal Intensive Care Unit
at University College London Hospital has shown survival rates
in the period 1996 to 2000 of 42% at 23 weeks and 72% at 24 weeks.
14 Survival at 22 weeks of gestation is unusual but has been observed
in a number of major neonatal centres. In long-term follow-up
studies, a significant minority of extremely preterm survivors
have had some form of neurodevelopmental impairment with significant
disability identified in 15-25% of survivors.
17. Obstetric and neonatal care are continuing
to change and improve at an extraordinary pace. By their very
nature, long-term outcome studies represent the outcome following
a standard of care which has become outdated. Since the nationwide
EPICURE study in 1995 there have been very significant and wide-reaching
improvements in the quality of care provided, in the frequency
of in-utero transfer to major perinatal centres, the level of
training of neonatal and obstetric staff, the provision of specialist
resources, and the educational and behavioural care and therapeutic
resources which are available to disabled children following discharge
from hospital. Hence historical data must be used with appropriate
caution when applied to children born in the present.
18. The data from recent studies indicate that
there has been continuing improvement in the survival of extremely
preterm infants over the last 15-20 years with very substantial
numbers of infants now surviving at 23 and 24 weeks of gestation.
Although major improvements in survival at these gestational ages
seem unlikely in the next few years, it is likely that continuing
advances in neonatal and obstetric care will lead to incremental
improvements in survival and to reductions in long-term morbidity.
REFERENCES
1. Thorp JM, Hartmann KE, Shadigian E. Long-term
physical and psychological health consequences of induced abortion:
review of the evidence. Obstetrics Gynecology Survey 2003; 58:
67-69.
2. Rooney B, Calhound BC. Induced abortion
and risk of later premature births. Journal of American Physicians
& Surgeons 2003; 8: 46-49.
3. Moreau C, Kaminski M, Ancel PY et al.
Previous induced abortion and the risk of very preterm delivery:
results of the EPIPAGE study. BJOG 2005; 112: 430-437.
4. Ancel PY, Lelong N, Papiernik E et al.
History of induced abortion as a risk factor for preterm birth
in European countries: results of the EUROPOP survey. Human Reproduction
2004; 19: 734-740.
5. Muhlemann K, Germain M, Krohn M. Does
abortion increase the risk of intrapartum infection in the following
pregnancy? Epidemiology 1996; 7: 369-376.
6. Murphy D J, Sellers S, MacKensie I Z,
Yudkin P L, Johnson A M. Case-control study of antenatal and intrapartum
risk factors for cerebral palsy in very preterm singleton babies.
Lancet 1995; 346: 1449-54.
7. Wu YW, Colford JM. Chorioamnionitis as
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284: 1417-24.
8. Resch B, Vollaard E, Maurer U et al.
Risk factors and determinants of neuro- developmental outcome
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2000; 159: 663-70.
9. Birth Statistics 2005, Office for National
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10 Ancel PY, Lelong N, Papiernik E et al. History
of induced abortion as a risk factor for preterm birth in European
countries: results of the EUROPOP survey. Human Reproduction 2004;
19: 734-740.
11. Wood NS, Marlow N, et al. Neurological
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and long-term neurodevelopmental outcome of extremely premature
infants born at 23-26 weeks gestational age at a tertiary centre,
Pediatrics; 2004; 113: e1-e6.
13. Doyle LW and the Victorian Infant Collaborative
Study Group, Intensive care at the borderline of viability—is
it worth it? Early Human Development 2004; 80: 103-113.
14. Riley K, Roth S, et al. Changes in survival
and neurodevelopmental outcome in 22 to 25 weeks gestation infants
over a 20 year period (abstract). European Society for Pediatric
Research, Annual Scientific Meeting 2004.
September 2007
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