Over 35, Pregnant, and NOT Geriatric!
Published on: April 13, 2022
Traditionally, pregnancy over 35 has been judged as high risk for both mother and baby. Midwife Emma McNerlin explores the evidence surrounding this contentious issue in maternity care.
By Emma McNerlin
Pregnant women are many things but they are NOT geriatric!
Since the 1970s, women have been increasingly delaying motherhood until their thirties and beyond as a result of increased availability of birth control, as well as socio economic factors such as access to higher education and better employment opportunities. In the UK, 24% of the babies born in 2020 were to mothers aged over 35, and 4.79% to mothers over 40 (ONS UK, 2020). The same trends can be observed in the USA where, in 2019, over one in six pregnancies were in women over 35 (CDC, 2021).
Despite the advancement of women’s rights over the past 40 years, the language used by physicians to describe pregnancy over 35 remains problematic. Traditionally referred to as ‘geriatric mothers’ or ‘elderly’, these unhelpful terms stigmatized those who delayed pregnancy or continued to add to their families beyond the age of 35. Their pregnancies were labeled as high risk, and thus medically managed with early induction of labor or scheduled C-sections, both options being deemed safer for women and their babies. Now called ‘advanced maternal age’, the term offers a slight improvement, but still suggests fragility, increased risk, and the need for caution. So, let’s explore what the evidence says about the risks of pregnancy over 35 and what the current implications are for managing these pregnancies.
Protocols and policies in healthcare should always be based on the best available evidence. However, in obstetrics this presents challenges because randomized control trials may not always be an ethical choice. For example, it is not ethical to randomize a woman to have a C-section for the sake of research when the procedure may present extra risks to mother and baby. Research on maternal age and pregnancy relies on large retrospective population studies. Data mining across multiple countries and decades produces statistics that are often incomplete or poorly controlled, making them unreliable to determine the actual risk of pregnancy after the age of 35. Although studies are becoming more targeted and have improved in the last ten years, many protocols remain based on outdated research (Dekker, 2021).
Googling ‘advanced maternal age risk’ results in some alarming headlines about being 50% more likely to have a miscarriage or stillbirth than a woman under 35. However, this does not mean that one in two pregnancies in women over 35 results in miscarriage or stillbirth. The headlines are sensational and scary, and they are misleading. The studies they refer to compare the relative increased risk of the outcome for over 35s versus those under 35. To put them into context we need to also know the absolute risk of the outcome for each group (under and over 35). This figure will give a number per 1,000 births in the group.
Table 1 shows an example of absolute risk of stillbirth by age from a large, well-designed and controlled Dutch study of 1.6 million births by Kortekaas et al in 2019. The results give a number per 1,000 births in the group. This study excluded pregnancies identified as high risk for reasons other than age, making the data more reliable.
Table 1: Kortekaas et al, 2019
|No. of stillbirths per 1,000 births||% stillbirth rate|
When looking at the absolute risk, it is clear that even in the over 40s in otherwise healthy women, the absolute risk of stillbirth is low. Imagine a room of 1,000 pregnant women over 40. This data shows that 997 of them will have a live birth. The researchers also found that gestational age is significant, with the risk of stillbirth increasing for all women between 39 and 40 weeks—1 out of 1,000 women under 35 and 1.4 per 1,000 women over 35. And yet all of the women in the upper age category would be encouraged to plan an earlier birth by induction or C-section to avoid the stillbirth ‘risk’ (Stone, 2021).
Whilst the absolute risk remains low, evidence shows that even when controlling for all other causes, maternal age is identified as a stand-alone risk factor for stillbirth, miscarriage, and other adverse neonatal outcomes (Reddy et al, 2006). The reasons for this are not completely understood. It is thought that placental function diminishes with age as hormone levels fluctuate. This is a reasonable hypothesis. Female babies are born with all of their eggs, and with age these decline in both number and quality, so the placenta that develops from the older egg may not function as well or produce sufficient hormones to nourish and sustain the pregnancy.
New research from the University of Manchester (Manchester Advanced Maternal Age Study or MAMAS) has identified biomarkers in the placenta that may help to predict pregnancies at risk of these adverse outcomes, including a small or growth restricted baby, stillbirth, NICU admission and low Apgar score at 5 minutes (Heazell et al, 2021). They also found that having a previous child earlier than 35 protects from a lot of these adverse outcomes. More research is required in this area, but initial findings are promising for more targeted interventions in pregnancies in over 35s.
Rates of miscarriage (defined as pregnancy loss before 20 weeks) increase with maternal age (CDC, 2021). A 2019 study by Magnus of registered pregnancies and their outcomes determined that the risk of miscarriage related more to the age of the egg and the increased likelihood of pre-existing medical conditions in the pregnant woman. The data showed that the risk of miscarriage among those aged 20 to 34 was 10–11%, at 35 to 39 it rose to 17%, for 40 to 44-year-olds it was 33%, and for those over 45 it was 57%. Medical advancements in harvesting and freezing eggs earlier in life, as well as the use of donor eggs, or embryos, referred to as third party reproduction, are all helping women to reduce their risk of miscarriage over 35.
We know that over half of all miscarriages are caused by genetic or chromosomal conditions in the fetus (March of Dimes, 2017). The risk of developing chromosomal abnormalities increases with the age of the egg. The most common chromosomal condition is trisomy 21 or Down syndrome. This condition varies in severity, and it is strongly correlated with pregnancies of advancing age. For example, the incidence in pregnancies at age 25 is 1 in 1,064, and by age 40 the odds have increased to 1 in 85. Other trisomies include trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome). These are relatively less common than Down syndrome, but also closely correlated with increased maternal age. Advances in fetal screening have meant that tests such as NIPT and PANORAMA—with over 99% sensitivity from as early as 9 weeks of pregnancy—have identified those affected by chromosomal conditions, thus helping families to access genetic counseling, and providing peace of mind to those whose screening returns a low risk result.
As we age, our risk of developing lifestyle-related conditions such as hypertension, diabetes, and obesity increases. ACOG (2020) recognized that women over 35 are more likely to suffer from hypertension (high blood pressure), gestational diabetes, preeclampsia, and experience premature birth and low birth weight babies. It is also more likely over the age of 35 that women may use assisted fertility to get pregnant. IVF, IUI, and medications to promote ovulation all come with increased risk. We cannot stop time; nothing will stop us getting older. However, focusing on good preconception care, eating well, exercising regularly, and giving up smoking and alcohol before trying for a baby—at any age—will increase your chances of a fit and healthy pregnancy.
In reality, there is no internal obstetric risk switch that turns on at 35. Many risks do not increase significantly until over the age of 40, and more markedly at over 45 (Jolly et al, 2000). And yet that label of ‘advanced maternal age’ can make you feel really old when you are just 35! (Cohen et al, 2021). The reporting of risk in pregnancies over 35 needs to be clear and non-judgmental. If in doubt, always ask for absolute risks, not relative risks, and ask what evidence they are based on.
Despite all of the studies on risks, there are still gaps in our knowledge of what we need to do to support a woman who becomes pregnant after 35. There is little research on women’s experience of maternity care beyond this age (Lampinen, 2009). Also, in spite of evidence linking advanced paternal age to increased stillbirth rates and low birthweight babies (Eisenberg, 2018), we do not discourage men from becoming parents at 35, most likely because we talk about this factor less. It is essential that women are presented with the evidence and supported to make an informed decision that is right for them, be that a planned C-section at 39 weeks, or expectant management for spontaneous labor. Ultimately, women need to be trusted to make the decisions that they feel are right for them and their babies.
Office for National Statistics UK (2020) Births in England and Wales: summary tables. ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/livebirths/datasets/birthsummarytables
CDC (2021) Births: Final Data for 2019. cdc.gov/nchs/data/nvsr/nvsr70/nvsr70-02-508.pdf
Dekker (2021) Evidence on: Pregnancy at Age 35 and Older. evidencebasedbirth.com/advanced-maternal-age/
Kortekaas et al (2019) Risk of adverse pregnancy outcomes of late- and postterm pregnancies in advanced maternal age: A national cohort study. obgyn.onlinelibrary.wiley.com/doi/pdf/10.1111/aogs.13828
Stone (2012) Advanced maternal age and the risk of antepartum stillbirth. wftinc.org/wp-content/uploads/2019/02/SMF-Stillbirth.pdf
Reddy et al (2006) Maternal age and the risk of stillbirth throughout pregnancy in the United States. singer.ch/pdf/Reddy%202006%20IUFTRisk.pdf
Heazell et al (2021) A prospective cohort study providing insights for markers of adverse pregnancy outcome in older mothers. pubmed.ncbi.nlm.nih.gov/34670515/
Magnus et al (2012) Role of maternal age and pregnancy history in risk of miscarriage: prospective register based study. bmj.com/content/364/bmj.l869.long
March of Dimes (2017) Miscarriage. marchofdimes.org/complications/miscarriage.aspx
Jolly et al (2000) The risks associated with pregnancy in women aged 35 years or older. pubmed.ncbi.nlm.nih.gov/11056148/
Cohen et al (2021) Association of Prenatal Care Services, Maternal Morbidity, and Perinatal Mortality With the Advanced Maternal Age Cutoff of 35 Years. jamanetwork.com/journals/jama-health-forum/fullarticle/2786896
Lampinen et al (2009) A Review of Pregnancy in Women Over 35 Years of Age. ncbi.nlm.nih.gov/pmc/articles/PMC2729989/
Eisenberg et al (2018) Association of paternal age with perinatal outcomes between 2007 and 2016 in the United States: population based cohort study. bmj.com/content/363/bmj.k4372
ACOG (2020) Having a Baby After Age 35: How Aging Affects Fertility and Pregnancy. acog.org/store/products/patient-education/pamphlets/pregnancy/having-a-baby-after-age-35
Photos from Canva.
About the Author
Emma McNerlin is a UK trained and registered Midwife, First Aid Instructor, and owner of Bumpsy Daisy Café and Community; a cafe and parenting community center for new and expecting parents offering birthing classes, hypnobirthing, First Aid workshops, and baby classes.
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