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What's the problem with older mothers?

1) What is the trend towards later motherhood?

The Office for National Statistics (ONS) reports [LINK: http://www.ons.gov.uk/ons/dcp171778_330664.pdf] that in 2012, nearly half (49%) of all live births were to mothers aged 30 and over, and that nearly two-thirds (65%) of fathers were aged 30 and over. A more precise account of the figures reveals that about 29% of births are to women aged 30-34, 16% are to women aged 35-39, 4% are to women aged 40-44, and less than 1% are to women over 45.

One in 25 babies are now born to the over-40s, a four-fold increase in 30 years.

Live births by age group of mother, 1938-2012

Births by age group, chart - 1938-2012

Source: Live Births in England and Wales by Characteristics of Mother 1, 2012. Office for National Statistics licensed under the Open Government Licence v.3.0.

The rise in maternal age is part of an ongoing social trend over the past five decades. It reflects the fact that in the twenty-first century, women have access to effective contraception, and this gives them the scope to construct their lives around choices about partners, careers, and friendships.

The magnitude of changes to people's sexual choices and behaviour was indicated in the third National Survey of Sexual Attitudes and Lifestyles (Natsal) published in December, from which the lead authors Kaye Wellings and Anne Johnson concluded, 'sexual activity is not primarily, or even necessarily, about reproduction'.

In this situation, having children is best seen not as a 'natural' part of life, but as a personal act by a couple, which has a necessary biological component. There is no right to have a child, and it is not always possible to control whether one becomes pregnant or not. But in twenty-first-century Britain, it is not generally biology that pushes women to have babies, but personal decision-making, which takes place within a wider social context.

Some of the social and cultural trends that affect the timing of motherhood are worthy of debate. That women are having babies later in life is neither an obviously good thing, or an obviously bad thing. But many of these social and cultural debates tend to be played out through a discussion of the clinical problems about older women's ability to carry a pregnancy in their thirties and give birth to a healthy child.

This tends to simplify and distort the science around fertility, and panic many women when their chances of having a baby at the time that is right for them are high. Research by bpas shows there is disproportionate concern among women about their fertility, and a tendency to overestimate the difficulties that may be encountered conceiving at the age of 35.

2) What is the problem claimed to be?

The idea that delayed motherhood poses a problem, for women, babies and for the health service, has become widely aired in recent years. In January 2014, England's Chief Medical Officer, Professor Dame Sally Davies, aired concerns about 'the “steady shift” towards women choosing to postpone starting a family until their late 30s and early 40s, reducing their chance of conception, and increasing their medical risks'.

The Royal College of Midwives has suggested that older mothers are placing an increased strain on midwives, who are already conducting close to 130,000 deliveries a year for which they do not have sufficient resources. Jacque Gerrard, RCM director for England, stated:

'Older women are more at risk of preeclampsia, miscarriage and complicated pregnancies which could result in use of forceps or caesarean section.'

The 'public health perspective' on later maternal age is seen to be so conclusive that the Royal College of Obstetricians and Gynaecologists (RCOG) in 2009 issued a statement about it. After noting that '[b]iologically, the optimum period for childbearing is between 20-35 years of age' and reviewing the relatively unfavourable outcomes for conception rates and pregnancy outcomes above that age, the statement cautioned:

'For these reasons, the Royal College of Obstetricians and Gynaecologists and doctors would encourage women to consider having families during the period of optimum fertility.'

However, the existence of a 'period of optimum fertility' does not mean that the door slams shut the minute a woman reaches 35. If a woman wants just 2 children, the chances of her being able to achieve this in her mid- to late thirties remain high. As a 2014 commentary by the US obstetrician WR Cohen in the British Journal of Obstetrics and Gynaecology (BJOG) concludes, after reviewing the extent to which maternal age affects pregnancy outcome:

'it is important to remember that the great majority of pregnancies in older women are relatively uncomplicated and end quite satisfactorily. Our role is to identify those that will benefit from our help.'

3) How is getting pregnant affected by age?

The fertility statistics show that increasing proportions of women are having children in their late 30s. The abortion statistics show, further, that a sizeable proportion of women have unintended pregnancies at this age.

In 2012, almost 27,000 women aged 35 and over had an abortion; and this number and rate has remained stable since 2002. This is despite the fact that the percentage of conceptions leading to abortion has generally decreased for women aged 35 and over in the past 20 years, reflecting the trend towards later motherhood.

Conceptions: percentage leading to legal abortion by age of woman at conception, 2011

Conceptions in England and Wales leading to abortions, chart

Source: Conceptions in England and Wales, 2011. Office for National Statistics licensed under the Open Government Licence v.3.0.

The RCOG states that 'within a year, 75% of women aged 30 and 66% of women aged 35 will conceive naturally and have a baby. After this, it is increasingly difficult to fall pregnant, and the chance of miscarriage rises.' Age-related infertility is a continuum, and it does indeed become 'increasingly difficult to get pregnant' over the age of 35. But the question is precisely how much more difficult it becomes.

The widely citied statistic that only 66% of women aged 35 to 39 will be pregnant after a year of trying if based on a 2004 article in the journal Human Reproduction, which in turn is based on an analysis of French birth records from 1670 to 1830. The attraction of using data from a pre-modern population is the fact that the data is not distorted by the use of birth control. But as the psychologist Jean Twenge points out in her review of the literature, this was "a time before electricity, antibiotics, or fertility treatment".

For modern women, the reality is far better expressed in a 2004 study by David Dunson and colleagues, published in Obstetrics and Gynecology. This found that, if they were having sex twice a week, 82% of women aged between 35 and 39 fell pregnant within a year. However, what made the biggest difference was the frequency of intercourse: if women had sex once per week instead of twice, 'the rates of infertility increase substantially to 15%, 22–24%, and 29% for women aged 19–26, 27–34, and 35–39 years, respectively'.

Dunson et al. also found that 'age of the man also has a large effect on time to pregnancy and the proportion of couples classified as clinically infertile'. 'For men younger than 35 years, there is no effect, but starting in the late 30s, the impact of male age becomes pronounced,' they write. 'The effect on fertility of a man aging from 35 to 40 is about the same as the effect seen when intercourse frequency drops from twice per week to once per week'.

Dunson et al. concluded that:

'Increased infertility in older couples is attributable primarily to declines in fertility rates rather than to absolute sterility. Many infertile couples will conceive if they try for an additional year'.

In other words: women in their thirties might have to try harder to get pregnant, particularly if their partner is also in his late thirties. However, their age alone is unlikely to make them infertile.

The science of the issue is backed up by our experience of modern life. The social trend towards later motherhood, which is evidenced by the growing number of mothers in their 30s, indicate that getting pregnant is not a problem for the majority of women aged 35-39.

However, this does not mean that all women who want to get pregnant in their late 30s will be able to – and this is really where the problem lies. Population-level data cannot predict individual experience; so statistics cannot tell us when, exactly, an individual woman's fertility begins to decline. We know that in general, women aged 35-39 have a reasonable chance of getting pregnant; but when an individual woman aged 36, or 38, tries to become pregnant she might not always succeed.

This could be related to her age: for example, the RCOG notes that early ovarian ageing happens in around 10% of women in the general population. In other words, a woman in her late 30s may experience infertility not because she is 'typical' of women her age, but because she is untypical. At a purely biological level, if this woman had tried to conceive earlier, she would have had a better chance of becoming pregnant. However, even these situations require caveats.

Like early menopause and a host of other problems that can lead to infertility, or difficulties in conceiving, such as endometriosis, polycystic ovary syndrome, or blocked fallopian tubes, early ovarian ageing can happen at any point during a woman's reproductive lifetime; and unless a woman is actively trying to become pregnant, she may not realise that she has these problems.

It is misleading to call these problems of 'age-related infertility' – they are just problems of fertility. Where it relates to a woman's age is in the implications of resolving the problem. And it is this, in fact, where much of the recent angst about the 'biological clock' comes from.

4) What are the additional complications in pregnancy and birth for women over 35?

The literature on delayed fertility pays great attention to the 'adverse outcomes' of pregnancy and birth in older women. There are three main concerns raised here:

a) The association between later pregnancy and specific pregnancy complications (eg hypertension).

b) That women becoming pregnant later in life are more likely to experience general age-related health conditions, such as diabetes, obesity, and decreased cardiovascular reserve.

c) The likelihood that the birth itself will have more complications.

Again, the data on pregnancy complications is extensive. The studies cited below indicate the kind of problems that are associated with pregnancy and neonatal outcomes in older mothers.

1990 study in the New England Journal of Medicine differentiated between pregnancy complications and outcomes for the babies. This study found that while there was a slight elevation in the risk of having a low-birth-weight baby among women aged 35 or over:

'there was no evidence that women between 30 and 34 or those 35 and older had an increased risk of having a preterm delivery or of having an infant who was small for gestational age, had a low Apgar score, or died in the perinatal period'.

But while the outcomes for babies were good, the study also found that 'women who were 35 or older were significantly more likely to have specific antepartum and intrapartum complications and those who were 30 or older were significantly more likely to have both caesarean sections and infants who were admitted to the newborn intensive care unit'.

2007 study in Human Reproduction of women aged 30-54 found 'an increased risk of infant death with advancing age for both primiparas and multiparas, even after controlling for the presence of congenital anomalies.' For mothers:

'The risks for most outcomes paralleled increasing maternal age including prolonged and dysfunctional labour, excessive labour bleeding, breech and malpresentation and primary Caesarean delivery.' The authors concluded that 'Increasing maternal age is associated with significantly elevated risks for pregnancy complications and adverse outcomes, which vary by parity.'

The general point here is that there are relatively higher risks to older mothers and their babies than to younger mothers. But again, we should take care not over-simplify the findings, in either direction. In both studies, delivery by C-section is reported as an 'adverse outcome'; yet this surely relies on a number of other factors that influence clinical judgements.

For example, the NEJM study authors concede:

'It may be that the higher rate of caesarean section as well as the higher rate of admission to the newborn intensive care unit among the infants of the older mothers in our study reflects greater vigilance and more conservative treatment of older primiparous women and their newborns.'

The 2014 BJOG commentary by WR Cohen by WR Cohen makes a similar point. When it comes to explaining 'why caesarean is so prevalent among older women', he writes:

'Undoubtedly, several factors, both social and biological, are at work. The high rate can be explained only in part by obstetric and medical comorbidities and the propensity of older women to have dysfunctional labour. How much of this intervention is related to physicians' or parents' subjective sense of urgency or anxiety about outcome is uncertain, but is probably a factor, even if it defies prudence and rationality.'

2014 study of Irish women by DA Vaughan et al. found 'an escalation in rates for all categories of caesarean section with maternal age, suggesting that management decisions both electively and in labour have an important impact on caesarean section rates, over and above physiological factors. This may reflect maternal preferences, obstetrician prejudices or a lowering in the threshold for risk-avoidance.'

In other words: while the risks of pregnancy complications increase with age, this does not mean that women having babies at the age of 35 or over are de facto putting themselves or their babies at increased risk.

The RCOG's statement puts the following balance on it:

'Most pregnancies will result in a healthy baby. However, adverse pregnancy outcomes also rise with age, and women over 40 are considered to be at a higher risk of pregnancy complications.'

A host of factors affect a woman's likelihood of developing pregnancy complications or adverse neonatal outcomes, from her socioeconomic status to her general health; and maternal age is best understood as one of these factors, rather than the sole determinant.

As WR Cohen spells out, women are all different, and 'chronological age does not necessarily equate with an individual's biological age or health'. If there were 'some biomarker of general ageing, and of reproductive ageing in particular', this would enable us to 'identify the large subset of women over 35 or 40 whose pregnancy-related risks are not substantially increased by their age, and others whose probable outcomes engender less optimism.'

Whatever the age of the mother, the process of pregnancy and birth themselves pose a level of risk to the woman and her baby, through hypertension, bleeding, difficult labours and so on. The issue at stake here is only how much additional risk is posed by advanced maternal age.

It is not that childbirth is safe for younger women, and dangerous for older women – indeed, the 2014 Irish study focuses on delivery outcomes for women at both 'extremes' of maternal age: those aged 17 and under, and those aged 40 and over. But even for women in the 'period of optimum fertility', childbirth can be hazardous: it might become slightly more so in some respects as the woman gets older.

2005 study in Obstetrics and Gynecology finds that: 'The majority of studies are optimistic with regard to maternal and neonatal outcomes' in older mothers. This study delineated between women aged 35 or younger, women aged 35-39, and women aged 40 or older. This study found that ages 35-39 'were associated with a statistically significant increased risk for fetal/neonatal congenital anomalies, gestational diabetes, placenta praevia, macrosomia, and caesarian delivery.' Crucially, however, '[t]he clinical significance of these associations in practice was less clear':

'That is, while women aged 35-39 years were significantly more likely to experience one of these outcomes statistically, the level of increased risk was not overly large and should be interpreted cautiously.'

5) How are fetuses affected by later maternal age?

One of the most well-known risks of later maternal age is the incidence of certain types of fetal anomaly, in particular Down's, Edwards' and Patau syndrome – or trisomies 21, 18 and 13. Over half of babies with Down's syndrome are born to mothers who are under 35. However, the overall risk for women having a baby at the age of 40 remains relatively low – 99 out of 100 women will not have a pregnancy affected by Down's syndrome. With Down's syndrome, the age breakdown is:

  • 25 years of age has a risk of 1 in 1,250
  • 30 years of age has a risk of 1 in 1,000
  • 35 years of age has a risk of 1 in 400
  • 40 years of age has a risk of 1 in 100
  • 45 years of age has a risk of 1 in 30

Even if they have not undergone fertility treatment, older women are also naturally more likely to have twins or triplets, which as well as having a higher risk of congenital anomalies (around 5% more common in multiple pregnancies than in singleton pregnancies), are also at risk of growth restriction and preterm birth, which in turn is associated with other complications such as cerebral palsy and learning difficulties. Multiple pregnancy is also associated with higher risks for the mother. Women carrying more than one baby have an increased risk of anaemia, hypertensive disorders, haemorrhage and postnatal illness. In general, maternal mortality associated with multiple births is 2.5 times that for singleton births.

6) What should health professionals and policymakers do about the trend towards older motherhood?

The clinical objections to delayed motherhood can be summed up in two statements. In terms of one's reproductive capacity, it is better to have babies younger; and in terms of one's health generally, it is better to be younger. It is impossible to argue convincingly against either of these statements in their own terms. They are just true.

With all this going on, doctors and policymakers need to tread very carefully when issuing messages to women about how they time their childbearing. On one hand, it is important to be honest, and recognise that a woman who is biologically infertile cannot get pregnant just because she wants to. At a general level, the evidence strongly suggests that women are likely to find the process of conceiving, being pregnant, and giving birth more straightforward if they are under 40, and there is little to be gained from denying that this is the case.

We should also be honest in saying that the context in which women make their fertility choices is not necessarily ideal, and it would be better if young mothers stood a decent chance of being career women too. Questioning the demands placed on women by today's culture of 'intensive parenting', and putting the case for affordable, flexible childcare, are as important for women as is protecting their ability to plan the timing of their families through contraception and abortion.

But part of being honest means that we should not over-inflate the problem. The continual conflation of the problems facing women at aged 35 with those aged over 40 seems deliberately designed to present women with a worst-case scenario, as though there is a need to scare women in their early thirties into rushing into pregnancy. The likely reality is that more women will have children in their mid to late thirties, and the likely outcome of that is that most pregnancies, births, and babies will be healthy.

Fertility treatment is expensive and uncertain, but most women know that already: and they also know that it can work in some cases. Being aware that fertility treatment exists as a last resort does not encourage women to 'put off' having babies, just as knowing that abortion is there when contraception fails does not stop women from using contraception. Women respond, not to journal articles and pronouncements from Royal Colleges, but to their personal circumstances and the experiences of those around them. These circumstances and experiences suggest to them that having babies in one's thirties is quite normal.

If policymakers are worried by the consequences of later maternal age, they should be focusing on supporting prenatal screening services, preparing maternity services to be better able to cope with obstetric complications, and funding decent miscarriage care and fertility treatment. What they should not be doing is nagging women to get pregnant before they are ready, just so they fit neatly into the 'period of optimum fertility'.