Age before baby
What is the optimal age to get pregnant? With the
average age of New Zealand women having a child now at an all-time
high of 30, it seems obvious that with the age of first parenthood
increasing, women's fertility is decreasing. Fertility specialist
Dr Richard Fisher looks at the research surrounding how age impacts
on fertility, for both men and women.
Social change is always fascinating. Changes in the way we
behave often lead to unintended consequences. One of the most
significant adverse consequences arising from the change to older
parenthood (long held to be consequentially "good for society") is
that the incidence of subfertility is increasing for many couples.
For many, conception is easy; but for an increasing number, it is
becoming more difficult. This is not because there is a fundamental
change in human ability to reproduce, it is simply a side effect of
beginning one's reproductive life later than in the past.
The average age of first birth in New Zealand has climbed steadily
since the 1970s. The situation now in 2008 is that it has reached
28. The average age of all New Zealand women giving birth is around
30 years. Clearly this is only an average, but what it does mean is
that a significant number of people are trying to have their first
baby later than they used to.
Human fecundity (the chance of conception per month) changes quite
dramatically over time, with good evidence that it begins to
decline in the late 20s and it falls more rapidly from the mid-30s.
At age 30, the average chance of conception per month is around
20%, and by age 35, it has fallen to around 17% or 18%. By 40 it is
down to 10% per month. At 43, most women have only around a 4% to
5% chance of conceiving each month.
Fecundity is a biological variable, and involves two people rather
than one, but the primary determinant is usually the woman's age.
That some women do conceive at 43 is certainly true, but also means
that a significant number will not conceive, through no fault of
their own, and with no underlying cause other than chance.
As women age, the likelihood of the egg that is released each
month being normal decreases, and by age 40, around 85% to 90% of
eggs are chromosomally abnormal.
At a time when couples would most like to conceive quickly, nature
determines that conception will, more likely than not, occur
slowly. To compound this, the incidence of miscarriage and later
fetal loss increases as age increases. The risk of miscarriage
increases from around 10-15% at age 30 to 35-40% at 40.
We have known for many years that there is an increase
inchromosomal abnormalities in the children of reproductively older
women, but recently, more interest has been shown in men's age as
an independent variable in reproductive outcomes. Lately there has
been some publicity about the chance of fetal death increasing as
male age increases, but this just confirms data known for some time
that a paternal age of greater than 50 doubles the chance of fetal
death at any time in pregnancy, and paternal age of more than 40
leads to an increased rate of miscarriage independent of maternal
More recent data has shown that as men age, the chance of
their partner conceiving reduces as well, and a man older than 40
may halve the chances per month of his partner conceiving. Young
sperm seems to have a significant biological advantage, just as
young eggs do.
Just as in women, paternal age can affect children's outcome,
although more recognised in non-chromosome abnormalities such as
schizophrenia, autism, and achondroplasia (dwarfism). The data
about schizophrenia seems particularly robust, with the chance of a
45-year-old male having a child with schizophrenia being three
times greater than one under 30. Similarly, as men age there is an
increased risk of the child having autism.
These are all relative risks, however, and the absolute levels
remain small. Men, however, clearly shoulder some of the burden of
risk factors with the changing reproductive age.
I am often surprised how many couples are unaware of the
significant effect of female age on reproduction. Despite 20 years
of my constantly talking about maternal age and its effect on
fertility, the information is still not widely disseminated, or, if
it is, not widely absorbed. Most people are brought up to think
about "when" they have children, rather than "if", and hold firmly
to the belief that such an "if" could not happen to them.
As always, there are competing messages in the media, which make
an assessment of likelihood difficult. News that yet another
celebrity has conceived in their 40s (and often with twins) often
lacks added information that their conception was assisted, and
often with the use of donor eggs. Hollywood must have the highest
incidence of spontaneous twin pregnancies in the world!
A consequence of this delay in attempting to conceive is that more
people present to infertility clinics for assistance than ever
before. Often there is no definable cause other than age, and with
luck, time alone will allow conception to occur. The average normal
37-year-old will take around seven to eight months to conceive, and
the average 40-year-old will take up to 15 months.
Clearly the underlying emotional pressures of such delays are
significant. The insecurity about conception leads to interventions
such as the use of drugs and even IVF, which,if more time was
available, might prove unnecessary.
Since 1990, there has been a four-fold increase in the use of IVF
in women over 40. Approximately 20% of all couples having IVF at
Fertility Associates Auckland are now over the age of 40. There is
little question IVF is the most effective treatment in any
individual month for these couples, although it is a complex
treatment, which most couples would rather have avoided.
Just as in natural conception, the success rates in IVF are also
limited by the underlying biology. IVF is a highly successful
treatment in younger women and a relatively effective one in older
women, but the incidence of failure increases with age.
It has been widely stated (without any factual basis) that
the reasons for delaying conception were primarily around women
deciding to become educationally, professionally and financially
more secure, quite apart from the independence that the
emancipation of women has brought. Two recent surveys, however, in
Australia and New Zealand, both of infertile couples, strongly
suggest that the lack of a suitable partner may well be the prime
determinant. Whether women are getting more fussy, men are becoming
less ready to commit, or whether there are just are not enough
suitable men to go around, it is a fertile topic for further
Reproductive medicine can do clever things, but if what we have is
a social problem, then we would be better off seeking a social
solution. No amount of good medicine, combined with good research,
is likely to make a significant difference to the number of people
presenting for fertility treatment who are successful, whereas
trying to conceive earlier certainly would.
A further, and just as interesting, social consequence of delay in
childbearing may take another generation to become obvious.
In most societies, grandparents have played an active role in the
upbringing of their grandchildren. In the last two decades, with
more women at work, that involvement has often become more
consistent as a source of childcare during the working week, and
respite care at other times. Even families separated by distance
have some more consistent involvement than in the past.
If the current patterns continue, then it will be very common for
grandparents to become first grandparents in their sixties and
seventies, at a time when active grandparenthood might be more
difficult both emotionally and physically. For an increasing number
of grandparents, the likelihood of great-grandparenthood will be
For most couples, conception should occur without too much
difficulty. Intercourse should not need to be planned like a
military exercise, but having an awareness of the time of ovulation
is important and having an awareness of the importance of age is
critical. If there is anything in your, or your partner's, history
which is suggestive of a reduction in your chances of
conception,such as pelvic infection, endometriosis, or surgery to
the testis, then you should present early for assessment. The more
irregular your cycles, the less predictable the time of ovulation
With social changes come unintended consequences. How we deal with
these particular consequences will shape the future for both
individuals and society as a whole.
Richard Fisher FRCOG,
FRANZCOG, CREI together with Freddy Graham established Fertility
Associates in 1987 after starting up New Zealand's integrated
infertility medicine group at National Women's previously. He is
New Zealand's foremost medical spokesperson on matters of
reproductive health and has been an advocate for better access to
care for couples with infertility throughout his career. He has
four children and is married to Leigh, without whom he could never
have practised medicine with the enthusiasm and commitment that he
will tell you more about Richard and the team at
As seen in OHbaby!
magazine Issue 3: 2008
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