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Birth After 40: Risks & Implications

Posted by Sarah Stogryn on


If you are over forty years of age and pregnant or planning a pregnancy, chances are good you've heard a lot about the risks involved: greater difficulty achieving and completing a pregnancy; greater risk of your baby being born with some form of disability or 'defect'; greater risk of maternal pregnancy health complications like pre-eclampsia, gestational hypertension, and gestational diabetes; greater risk of baby being born too early, too small, too big, or even being born still.  Just doing the research on this made my 35 year old ovaries start to get anxious. Today though, I'm going to skip past all the early stuff, and focus on the end of your pregnancy journey.  Let's say that you are 40+ years of age (yoa), a healthy weight both pre-pregnancy & currently, pregnant naturally, have had no fetal or maternal complications or red flags, and your due date is around the corner.  What does that mean for you?

There is a decent amount of research which shows that for a woman who is 40 or older, as you reach full-term in your pregnancy the risks of  your baby being born still are higher than for a woman who is younger (under 35 or under 30, depending on the study).  In very condensed form, it appears the risk of a woman 40+ years of age having a stillbirth at 40 weeks of pregnancy is *about* the same as the risk of a younger woman having a stillbirth at 42 weeks of pregnancy.  Because of this, many caregivers recommend that women who are 40+ yoa begin extra monitoring (like ultrasounds & non-stress tests to check amniotic fluid levels, placental function, fetal movements, fetal size, etc) beginning at 38 weeks, to help ensure fetal well-being and thus help reduce the risk of stillbirth.  Further to that, many caregivers recommend women who are 40+ yoa be medically induced at 40 weeks since they view it as being the equivalent to 42 weeks pregnant in terms of stillbirth risk.   Each of these monitoring tests carry their own risks, benefits, and margins of error which ought to be considered before they are undertaken.  Induction of labour for the prevention of stillbirth also carries benefits & risks.  A Cochrane review found that inducing women who are 40+yoa at 41 weeks gestation could reduce the risk of stillbirth, without an increased risk of cesarean section.  That doesn't mean however that induction of labour is necessarily the right choice for you.  Every woman has to decide for herself which risks she is most comfortable with; which paths feels right for her & her family.  Further links and resources on induction of labour are available at the bottom of the post.

Below, I have used data which Kim James CD(DONA) credits to the BMJ February 2001 issue, (columns indicated with a *).  However, I haven't been able to find this data on the BMJ website, and am unable to say if these figures are the stillbirth risk overall (including women of all ages, backgrounds, and risk-levels) or if these are only figures for a low-risk birth.  For the sake of argument let's say these are figures for ALL women (which is the most conservative way to view it and could artificially inflate the real risk level for women over 40 years of age, because essentially those of advanced maternal age would be 'weighted' twice within the statistics.)  
Because the majority of studies show that the risk of stillbirth doubles in women who are 40+yoa, I have done the math, and included those numbers below too (columns indicated with a ~). 

Week       Stillbirth Rate*   Likelihood of Living Baby*  Stillbirth Rate Women 40+yoa~     Likelihood of Living Baby~
36            .39:1000                    99.961%                                      .78:1000                                                   99.922

37            .30:1000                    99.970%                                      .60:1000                                                   99.94    

38            .52:1000                     99.948%                                     1.04:1000                                                 99.896   

39            .49:1000                     99.951%                                     .98:1000                                                   99.902

40            .87:1000                      99.913%                                     1.74:1000                                                99.826

41            1.27:1000                    99.873%                                     2.54:1000                                                99.746

42            1.55:1000                    99.845%                                    3.10:1000                                                99.69%

43            2.13:1000                    99.787%                                    4.26:1000                                                99.574%

According to the NEJM, women over 40 in recent decades (90's vs 60's & 70's) had twice the fetal death rate of women under 30 and "Even when we controlled for recognized coexisting conditions that contribute to fetal death, women 35 years of age or older continued to have a risk of fetal death that was twice as high as that among their younger counterparts." 

This BJOG study says that maternal obesity more than doubles your risk of stillbirth & neonatal death. 

And this BMJ study  says the single  greatest risk factor for stillbirth is undetected fetal growth restriction.

ACOG says in this study that "Perinatal mortality, intrauterine fetal death, and neonatal death increased with age. There was also an increase in intercurrent illnesses and pregnancy complications with increasing age, but this did not entirely explain the observed increase in perinatal mortality with age."

Some Canadian data on the correlation between advanced maternal age and birth defects.

SOGC's stance on pregnancy in women over 40yoa.

Soooo.... put all this together and what do you get?  Well the research up until Spring 2013 points to women giving birth over 40 years of age having a doubled risk of stillbirth compared to their younger counterparts, with some discussion about the need for further studies which clarify whether advanced maternal age is an independent factor, or if it is a factor because of other variables like weight-gain and diseases that are more prevalent in an older female population.  And while stillbirth is a terrible tragedy, which no family would ever intentionally choose, we need to remember in our decision-making that the overall risk is still small.  Using the above data table, we can see that the lowest risk of stillbirth exists at 37 weeks gestation, and the greatest risk exists for a woman 40+yoa at 43 weeks of pregnancy.  For the purposes of discussion though we're going to look at the risk level at 42 weeks as you'd be hard-pressed to find any caregiver okay with going past 42 weeks pregnancy anymore.  It's possible, but its rare.

Alright - here we go with the math:
At 37 weeks, for every 100,000 babies born, 30 will be born still.  Compare this to a 40+yoa woman at 42 weeks, and for every 100,000 babies born, 310 could be born still.  This is more than a ten-fold increase in the chance of stillbirth, or about a 1000% increase.  Sounds terrifying right?!  Let's soften it just a little and look at the difference between 40 weeks overall, and 42 wks for a 40+yoa woman.  Because even though the risk of stillbirth does seem to be lowest at 37 weeks, we don't routinely induce labour at 37 weeks because that carries so many other risks with it for both mother and baby.  Instead we'll work for a minute with the more typical 40 weeks.  At 40 weeks, for every 100,000 babies born, 87 will be born still.  Compare this to a 40+yoa woman at 42 weeks, and for every 100,000 babies born, 310 could be born still.  This is a 3.5 fold increase, or about a 350% increase.  Still pretty scary - I know! These numbers express the relative risk of a baby being born still, and if your doctor told you that there was a 350% greater chance of your baby being born still by waiting a full 42 weeks, most women would stop in their tracks.

What we also need to consider though, is the absolute risk, or the "hard" numbers.
At 37 weeks, there is a 99.970% chance that a living baby will be born.  And at a more standard 40 weeks, there is a 99.913% chance that a living baby will be born.  Compare this to the point when the risk is highest (43 weeks for a 40+yoa woman) and there is still a 99.574% chance that a living baby will be born. Or at 42 weeks, which is more commonly as 'far pregnant' as the medical system allows a women to be anymore, there is still a 99.690% chance of a healthy baby being born.  Say what??  Yup.  Even in the worst case scenario of the numbers available to me for an otherwise healthy mama-baby dyad, there is a greater than 99.5% chance that a living baby will be born.  Now that seems like a different story altogether doesn't it?

Of course, if you have other risk-factors like pre-existing health conditions, maternal or fetal complications or red flags, or social/environmental circumstances at play, then the risk of stillbirth for YOU could be increased, but not necessarily in a readily quantifiable way, as there just isn't enough research around all the possible areas of risk.  Science & Sensibility lays this out well here.

Which brings me to the newest study I've found on the topic.  I'm still trying to get my hands on the full report (well, without paying $40 for 24 hours of access!) and if any of my thoughts change after reading the whole thing I'll come back and let you know.   

This study from April 2013 (published in the journal of the International Society of Ultrasound in Obstetrics and Gynecology) examined "the association between maternal age and a wide range of adverse pregnancy outcomes after adjustment for confounding factors in obstetric history and maternal characteristics."  The study population included more than 75,000 women expecting a single baby and concluded that advanced maternal age (being 40+yoa) WAS associated with an increased risk of miscarriage, pre-eclampsia, gestational diabetes, babies being born small for their gestational age, and cesarean birth. This study also showed that being 40+yoa did NOT increase the risk of gestational hypertension, spontaneous preterm deliveries, or babies being born large for gestational age. Most importantly to me today, this study showed that being a woman 40+ years of age in and of itself, in the absence of other risk factors, does NOT increase the risk of stillbirth.  The authors concluded that

"Maternal age should be combined with other maternal characteristics and obstetric history when calculating an individualised adjusted risk for adverse pregnancy complications." 

And that right there pretty much sums things up as far as I'm concerned, when it comes to giving birth over 40yoa.  You need to look at the whole person - the big picture - and make an individual judgement about how to proceed in the final weeks of pregnancy.  If you have a very low tolerance for the risk of stillbirth (perhaps in the case of a mother who has already experienced a pregnancy loss), then inducing labour at 39 weeks or earlier might be exactly the right choice for you. Conversely, if you have a very low tolerance for the risks of increased fetal monitoring, induced labour, or cesarean birth, then waiting until 41 weeks or later may be your best path.  Either way, the mother and her family are the ones who have to live day by day with the results of her choices, which means that space must be made for her voice to be heard, and she must have both open ears and an open heart, to hear the voices of caregivers she trusts.  

If you are pregnant or planning a pregnancy, and 35+yoa, you can surround yourself with support by visiting The Advanced Maternal Age Project.

Want to know more about Induction of Labour?  Check out the links below:

A Timely Birth - Midwifery Today  

Induction of Labour Fact Sheet - CIMS

The Tree & The Fruit by Michel Odent in Midwifery Today

Induction of Labour: Balancing Risks - Midwife Thinking

Further resources related to natural induction of labour are available here on my resources page.


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