 
|
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Journal of the New Zealand Medical Association,
14-December-2007, Vol 120 No 1267
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Neonatal intensive care utilisation by infants born
to mothers older than 40 years of age: a 10-year review
Malcolm Battin, Coila Bevan, David Knight
Over the last 25 years a combination of social and
demographic factors have resulted in a notable drift upwards in the age at which
women in developed countries give birth to their children. In New Zealand, for
the first quarter of 2006, the median maternal age at birth was 30.4 years
compared with 28.7 years in 1996 and 25.1 years in
1975.1 Consequently, a large number of women
are having first babies in their mid-30s and a significant number are having
their first babies at age 40 or older. Indeed, at National Women’s
Hospital (Auckland, New Zealand) approximately 3% of deliveries are to women
over 40 years old.2 Although most women over
the age of 35 or even over 40 have healthy pregnancies and healthy babies, there
are potential problems associated with pregnancy at an increased maternal age.
These include declining fertility, and an increased rate of multiple
pregnancies; spontaneous pregnancy loss; medical complications of pregnancy;
intrauterine growth restriction; and prematurity and congenital anomalies,
including chromosomal abnormality.
Moreover, at the time of the labour and delivery, increased
maternal age is associated with higher risk of fetal distress, prolonged second
stage of labour, and increased rates of Caesarean
section.3–5 These factors (either alone
or in combination) may result in both short- and long-term neonatal morbidity.
While there is a reasonable body of literature regarding the
effect of advanced maternal age on obstetric outcome (including perinatal
mortality), there is a relative paucity of data on neonatal outcome, which is
often restricted to neonatal admission
rate.5–7 In one large study of births in
California in the early 1990s an increase in the proportion of infants coded as
having any birth asphyxia was reported following birth to nulliparous
women over 40 years but a lower rate of birth trauma was also reported perhaps
due to increased delivery by caesarean
section.8 Moreover, there are few published
series of temporal trends in utilisation of neonatal resources by infants born
to women of very advanced maternal age.
Therefore the aims of this study were two-fold. Firstly, to
quantify the requirement for neonatal intensive care in infants born to women
aged 40 years old or over during the period 1995–2004 inclusive. Secondly,
to evaluate trends in: demographic characteristics; neonatal mortality; neonatal
morbidity; and service utilisation, measured by duration of respiratory support
and stay on the neonatal unit.
MethodsData were reviewed for the 10-year period January 1995
to December 2004. All infants admitted to National Women’s Hospital
Neonatal Intensive Care Unit (NICU) and eligible for
registration with the Australian New Zealand Neonatal Network (ANZNN)
were identified from the National Women’s NICU database. The ANZNN
registration criteria included live born infants transferred from labour ward or
admitted to the participating hospital at less than 28 days of age with any of
the following: birth at less than 32 weeks gestation; birth weight less than
1500 grams; more than 4 consecutive hours of respiratory support, or major
neonatal surgery.
Ethical approval has previously been obtained for the
submission of de-identified data to the ANZNN from our hospital. For the time
period reviewed, National Women’s Hospital (NWH) provided all neonatal
intensive care to the central and Northern Auckland region which included
approximately 12,000 births annually.
The number of infants born to mothers in the age group
of interest was determined then appropriate clinical and demographic data were
reviewed. The dataset included a de-identified record of maternal age;
ethnicity, and past pregnancy history (including previous premature births),
previous perinatal death, and assisted conception.
Pregnancy data included plurality, presenting antenatal
problem, prolonged rupture of membranes, preterm labour, intrauterine growth
restriction (suspected antenatal), antenatal diagnosis of fetal malformation,
hypertension in pregnancy, antepartum haemorrhage, antenatal corticosteroids,
and (for multiples) birth order.
Delivery data comprised of presentation and mode of
delivery. Neonatal data—comprising gestational age, birth weight, Apgar
scores, resuscitation details, and respiratory diagnosis—measures
morbidity including highest lowest fractional inspired oxygen
(FiO2) in the first 12 hours, exogenous
surfactant use, air leak, days on positive pressure ventilation, days on
continuous positive airways pressure (CPAP), proven or suspected necrotising
enterocolitis (NEC), number of proven infections, intraventricular haemorrhage
(IVH), or other cranial ultrasound abnormality and retinopathy of prematurity
(ROP).
Important trends in both overall numbers of infants and
individual morbidities were examined. Data are presented as mean and standard
deviation if normally distributed, or as median and range if not normally
distributed. The data are presented by year or if more appropriate by 2- or
5-year epoch.
To demonstrate trends in graphs or tables (for total
number of infants, percentage of admissions, number of twins, deaths, days of
NICU care, and percentage of respiratory support) the epochs are 2-year blocks.
The two items of data that were used to indicate utilisation of neonatal
resources were total days hospital care prior to discharge and total days on
respiratory support during neonatal stay.
To explore differences in demographic
and presenting obstetric clinical data, the infants were divided into two time
periods (1995–1999 and 2000–2004) and the data compared. Incidences
were compared by Chi-squared and continuous data by Mann Whitney U test
or Student’s t-test as appropriate. Statistics were calculated
using Statview (Cary, NC USA) software.
ResultsFor the study period, 203 babies (who fulfilled ANZNN
registration criteria following birth to women older than 40 years) were
admitted to NICU at National Women’s Hospital. The presenting obstetric
clinical data and delivery mode are summarised Table 1.
Table 1. Antenatal complications and mode of
delivery for mothers aged 40 years and over (registered with Australian New
Zealand Neonatal Network) delivering babies in 1995–2004
On examining the data for trends in antenatal complications
there was an increase in the proportion of pregnancies coded as complicated by
suspected intrauterine growth restriction for 1995–1999 versus
2000–2004 (8% versus 14%, p=0.02) and in the proportion reported to have
spontaneous preterm labour (16% versus 39%, p=0.03) but no other significant
differences or trends in antenatal characteristics were detected.
There was no statistically significant difference in mode of
delivery between the two time periods 1995–1999 and 2000–2004.
Overall, there was a high rate of antenatal steroid use in pregnancies that
delivered prior to 34 completed weeks of gestation, with 100 of the 116 (62%)
receiving a full course and 72 of 116 (86%) receiving some steroid prior to
birth.
The median (range) gestational age and birth weight for the
infants were 33 (24–42) weeks and 2092 (570–5320) grams
respectively. Although there was wide variation in the range of values for the
individual years there was no clear trend by individual year or 5-year block in
either gestational age or birth weight. Overall, the majority of infants were
born in satisfactory condition with a median (range) Apgar score of 7
(1–9) at 1 minute and 9 (1–10) at 5 minutes respectively.
Indeed, only 80 infants (39%) and 24 infants (12%) had an
Apgar score below 7 at 1 and 5 minutes respectively. Resuscitation at birth
included intubation in 15.3% of infants. After admission to the neonatal unit,
33/203 (16%) received surfactant for respiratory distress syndrome.
In addition, one infant with meconium aspiration syndrome
received high frequency oscillation ventilation, five infants with pulmonary
hypertension received nitric oxide, and one infant with cardiac malformation
underwent extracorporeal membrane oxygenation (ECMO). There were no significant
trends in the proportion of infants requiring these interventions over time.
Mortality and acquired morbidities with long-term serious
consequences were uncommon. Eleven of the 203 (5.4%) infants died. There was no
overall trend in death when examined by individual year and no significant
difference in rate between the first and second time periods.
Neonatal morbidity included four infants with air leak
requiring drainage and eight infants diagnosed as having chronic lung disease (
five of these were discharged home receiving supplemental oxygen). Also four
infants had acquired neurological conditions that adversely affected outcome.
Specifically, there were two term infants with severe neonatal encephalopathy
that died and two preterm infants (25 and 28 weeks gestation) with major (i.e.
grade III/IV) intraventricular haemorrhage (IVH).
The infant with grade IV IVH died and the other who had
grade III survived. Other serious neonatal morbidity were uncommon; the median
number of proven infections was 0 (range 0–2), there was only one proven
and one suspected case of necrotising enterocolitis, and no cases of retinopathy
of prematurity (ROP) requiring treatment. Given the rarity of these morbidities,
trends were not assessed.
In addition to the acquired morbidity, several infants had
chromosomal abnormality, dysmorphic syndromes, or congenital anomalies that
would potentially affect outcome. Seven infants had major chromosomal
abnormality, this included Trisomy 21 in six infants and Trisomy 18 in one
infant. Three infants were diagnosed with an abnormal syndrome in the neonatal
period; one each of Prader Willi syndrome, Noonan syndrome, and Klinefelter
syndrome. In addition, nine infants had major congenital anomalies including
five with cardiac lesions and two each with skeletal or central nervous system
anomalies.
The five cardiac malformations included transposition of the
great arteries (TGA) in three cases, hypoplastic right heart ventricle in one,
and ventriculo-septal defect (VSD) in one. The two skeletal malformations were
missing digits from the hand in one case and syndactyly in the other. The two
malformations of the central nervous system were idiopathic microcephaly and an
occipital encephalocoele.
Important trends—including: total number of infants,
percentage of admissions, number of twins, deaths, days of NICU care, and
percentage of respiratory support—are summarised in Table 2.
The overall mean duration of neonatal admission was 32 days.
An increase was observed in the number of admissions, total days NICU care, and
percentage of total respiratory support from 1995–6 to a peak in
2001–2. Thereafter there was a small decrease in numbers but there were
changes in referral practice at that time, with the opening of other level two
neonatal units in the city.
Assisted conception, as recorded in the database (i.e.
reported by the women or lead maternity caregiver), was significantly more
common in the mothers over 40 years compared with those below 40 years of age
(15% versus 6.7%, p<0.001). Moreover, for infants born to mothers over 40 and
admitted to NICU, there was an increase in the proportion reported to be
conceived following assisted conception from approximately 9% and 13% for the
two time periods 1995–1999 and 2000–2004.
Changes in the contribution from the major ethnic groups
over time are presented in Figure 1. A rise was seen in number of New Zealand
European infants compared to stable numbers in the other ethnic groups.
Table 2. Summary of neonatal admissions and
care in infants born to women over 40 years old for the 10-year period
1995–2004
BW=birth weight; GA=gestational age; *2004 had referral
process changes with opening of other level 2 neonatal units.
Figure 1. Trends in the number of infants born
to mothers over 40 years of age, by ethnic group
 NZ Euro=New Zealand European; PI=Pacific Islander (e.g.
Samoan, Tongan, Niuean, Cook Islander).
 DiscussionNew Zealand, like many other developed countries, has
experienced a substantial increase in births to women over the age of 40 years.
For instance, over the last 10 years, National Women’s Hospital has
experienced an increase in deliveries to women in this age group from 1.5% to
approximately 3% of total deliveries.2
It is well recognised that with increasing maternal age
several factors (including increased rates of multiple births, medical
complications of pregnancy, and perinatal complications) result in more infants
with neonatal problems. This study examined trends over a 10-year period in a
single centre and demonstrated an increase in both the absolute number of
admissions and proportion of total admissions born to women aged over 40 years.
Although there have been concomitant changes in the rates of
delivery to older women and some changes the total number of admissions for
neonatal intensive care, it is notable that infants born to women over the age
of 40 account for 3% of deliveries but 5% of neonatal admissions. Further, these
demographic changes are associated with a significant increase in the workload
measured by total days neonatal care and total time on respiratory support for
this group of infants.
Despite the increase in birth numbers to women in the
over-40s age group, the presenting obstetric factors and infant characteristics
were fairly consistent. Specifically, the rates of prolonged rupture of
membranes, antepartum haemorrhage, hypertension in pregnancy, or fetal distress
were unchanged but there was a significant increase in multiple pregnancy,
spontaneous preterm labour, and suspected intrauterine growth restriction
(IUGR)—although the majority of the infants were neither extremely low
gestational age nor extremely low birth weight, with a median gestational age
and birth weight of 33 weeks and 2092 grams respectively.
The significant increase in multiple pregnancy may
contribute to the increase in premature birth. Also the increased IUGR rate may
be explained by better ultrasound detection and the use of individualized growth
charts.9,10
Even though the neonatal mortality and rate of serious
neonatal morbidities were both low, the admission for neonatal care is not
without consequence. Certainly the infants did receive a substantial amount of
respiratory support and the mean duration of neonatal admission was 32 days.
Interestingly, overall 16% got surfactant (to aid lung function) with no
significant change in rates between two time periods. Finally with respect to
the individual infant there is recent evidence that even if only moderately
premature there can be significant short term
morbidity11 and in the longer term this may be
associated with some cognitive impairment compared with matched
controls.12
The increase in numbers of infants receiving neonatal
intensive care following birth to women above the age of 40 years occurs
predominately in NZ Europeans. Full discussion of the complex social factors
responsible for the increasing maternal age is beyond the scope of this paper.
However, it is noted that Māori mothers tend to be younger with a median
age at birth of 26.0 years compared with 30.4 years in the overall population
2006.1 It is also clear that increased maternal
age is associated with difficulty conceiving and increased rates of assisted
conception.
Overall, 15% of the infants born to the older mothers were
reported to be the product of assisted conception. Furthermore, it is possible
that this was an underestimate of fertility treatment data as information may
not be forthcoming or not recorded at the time of pregnancy booking. However, a
steady increase in numbers was observed through the 10-year period. Twin births
following fertility treatment are at an increased risk of preterm birth, but are
mostly mildly preterm.13
In the study group, an increase in twins as both absolute
numbers and proportion of total admissions was seen with a peak in 2002. The
pattern for the reported use of fertility treatment and the rate of twin birth
were similar with an initial increases then, after 2002, a decline in rate seen
for both.
Although spontaneous twins are more common with advanced
maternal age, the recent decline in the twin rate almost certainly reflects
changes in fertility practice. Since 2004, or perhaps slightly earlier, there
has been a push for single embryo transfer.14
A potential limitation of the study is that it is from a
single centre. Certainly the apparent decrease in overall numbers after 2003 may
be a consequence of changes in neonatal admissions, as two other level two
neonatal units opened in the city.
Our hospital also possibly selects a greater proportion of
older women and the increased neonatal admission rate may not reflect the
general experience in New Zealand. However, this is unlikely that our unit is
the only one affected by these demographic changes given the national population
data illustrating an increase in the number of women who are now giving birth to
children after the age of 40. Nevertheless, further work is planned using ANZNN
data on all New Zealand admissions which will allow the study of trends for the
whole country rather than a single centre.
A second potential limitation of the study is that there
have been significant changes in neonatal respiratory care during the 10-year
period 1995–2004. Firstly, the increasing availability and use of
surfactant from the mid 1990s then increased CPAP use and a decline in both
ventilation and surfactant use in the late 1990s. In order to account for these
changes, the data on trends in respiratory support (Table 2) are calculated from
total time on respiratory support, i.e. calculated from combined ventilation and
CPAP duration.
In conclusion, infants born to mothers over the age of 40
years currently represent about 5% of admissions to the service fulfilling ANZNN
criteria. Their mortality and morbidity is fairly low, but admission numbers and
service utilisation (measured by total days care and respiratory support) has
markedly increased compared to 1995. Although the number of infants remains
quite low this increase in neonatal workload and change in maternal demographics
needs to be recognised and may have implications for service planning.
Competing interests: None.
Author information: Malcolm Battin, Senior
Lecturer (Neonatology)1,2; Coila Bevan Research
Nurse2; David Knight, Clinical Director of
Newborn Services2;
Correspondence: MR
Battin, Newborn Services, National Women’s Health,
9th Floor Support Building, Auckland City
Hospital, Private Bag 92 189, Auckland, New Zealand. Fax: +64 (0)9 6309753;
email: malcolmb@adhb.govt.nz
References:
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| | Current
issue | Search journal |
Archived issues | Classifieds
| Hotline (free ads) Subscribe | Contribute | Advertise | Contact Us | Copyright | Other Journals |
|