From a biological standpoint, there is a limited window for getting pregnant from reproductive age until menopause. While there is a big window of opportunity, there is never a perfect time to have a baby. You may end up expecting much sooner than you imagined, or life may work out that you end up pregnant much later. Due to the higher risk stigma of pregnancy after age 35 or social norms and expectations, many women feel pressure to have children before age 35. The technical term for having a baby over 35 is advanced maternal age. There is a classification for pregnant women over age 35 because many risks increase in this age group. Labeling an expecting mother who is 35 as a higher risk from the start can come along with anxiety and stress. There are also benefits to being a parent in your mid-thirties or older. This episode examines the evidence behind the risks associated with advanced maternal age and what pregnancy over 35 means for you and your baby.
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Defining Advanced Maternal Age
Advanced maternal age is a label applied to mothers who expect to have a baby after their 35th birthday. Even if you are not 35 now, you may have additional children as you get closer or go over this birthday. While you may not love the term ‘advanced maternal age,’ this is an improvement. Not long ago, doctors used the terms elderly primigravida for a first-time mother 35 and older or elderly multigravida for a mother over 35 with multiple children.
In 1970 the average age of a first-time mother in the United States was 21.4. By 2000 the average was 27.2. That number has remained relatively steady and was 27.3 in 2021. While the mean age has not changed much, the birth rate for women 29 and younger has steadily decreased, while the birth rate for mothers aged 30 and older has been increasing. According to ACOG, nearly 19% of all pregnancies in the United States are to mothers aged 35 and older. ACOG notes that observational studies demonstrate that pregnancy in older individuals is associated with increased risks of adverse pregnancy outcomes—for both the pregnant patient and the fetus—that might differ from a younger pregnant population, even in healthy individuals with no other comorbidities.
Don’t panic about being over 35 increasing your risks of adverse outcomes. For an expecting mother who is 35, labeling her as a higher risk from the start can understandably come along with anxiety and stress. Let’s dive into the research and take a closer look. There are also benefits to being a mother in your mid-thirties and beyond; we will examine those too.
The Perfect Age to Get Pregnant
There is never a perfect time to have a baby. You may end up expecting much sooner than you imagined, or life may work out that you end up pregnant much later. A lot of women feel pressure to have children before the age of 35. Part of that may be due to the higher risk stigma of pregnancy after age 35 and partially due to social norms and expectations. Whenever you are pregnant is the perfect time to be pregnant, no matter what your age is. Even if you have a plan of when you want to have children, it is challenging to time that perfectly. If you have more than one child, you may have them closer together than you anticipated or much further apart.
From a biological standpoint, there is a limited window for getting pregnant, from reproductive age until menopause. Menopause, when your menstrual cycles stop, can happen in your 40s or 50s, but the average age is 51 in the United States. Typically, in your late 30s, your ovaries will start making less estrogen and progesterone. In your 40s, you will likely see changes in your periods. On average, by age 51, you officially hit menopause, your ovaries stop producing eggs, and you have no more periods. Even with this limited window, there are several decades that you can biologically get pregnant.
Maternal Age is Increasing
We discussed the increase of older women having babies and that 19% of all pregnancies in the United States are to mothers aged 35 and older. The CDC releases statistics on births, and the most recent stats show the continuing trend of declining birth rates from age 15-24 and an increase from 30-44.
The rise in births to older mothers over the decades is due to more than just the decline in births to younger mothers. It is partially due to the availability of contraception, career opportunities, and advancement, improvements in assisted reproductive technology, and changes in social norms and attitudes. The rise in births to older mothers isn’t unique to the United States. The Organisation for Economic Co-operation and Development (OECD) released a report on the age of mothers at childbirth that includes data from 38 member countries. Most OECD countries have seen the average age of women at childbirth increase between 2 and 5 years between 1970 and 2020. With a few exceptions, the average age at which women give birth is 30 or older. Only Colombia and Mexico have a mean age of women at childbirth below 28; in only seven countries, including the United States, it is between 28 and 30. In all other OECD countries, the average age of women at childbirth is at least 30, and in Ireland, Italy, Japan, Korea, Luxembourg, Spain, and Switzerland, the average age is above 32.
Celebrity Pregnancies Over 35
A lot of celebrities are having babies in their late 30s and 40s.
J Lo, twins at 38
Drew Barrymore 37, 39
Gwen Stefani 36, 38, 44
Tina Fey 35, 41
Naomi Watts 39, 40
Salma Hayek 41
Uma Thurman 42
Alanis Morissette 44
Halle Barry 41, 47
Rachel Weisz 48
Janet Jackson had her first baby at 50.
Risks of Advanced Maternal Age
The American College of Obstetricians and Gynecologists is a professional membership organization providing educational resources and guidance to OBGYNs, setting standards, publishing guidelines and recommendations, and influencing public policy and legislation. ACOG greatly influences doctors and the medical system in general when it comes to pregnancy and birth. This is also the information likely informing your care provider. ACOG has frequently asked questions about having a baby after 35. Overall, ACOG notes quite a few pregnancy risks that increase over the age of 35. We will dive into each of these throughout this episode.
Age Stratification in Research
One thing that stood out to me as I researched for this episode is how study participants are broken into groups by age. Nearly every study groups expecting moms into age groups 30-34, 35-39, and 40+. In examining the 30-34 and 35-39 age groups, having the cut-off at 35 could skew results a bit rather than if you looked at each age separately. This trend in research can partially explain where the magic age of 35 comes from as the age at which the risk for many complications increases. The truth is that nothing magical happens regarding risks on your 35th birthday.
Overall Increase in Risk After 35
There is a lot of evidence that risks for many complications increase with age. One study of over 385,000 pregnancies found that pregnant women over 35 are at an increased risk of pregnancy complications compared to younger women. This study divided women into ages 18-34, 35-39, and 40+. Statistics from this study are used throughout this episode as we examine individual risks.
Fertility After 35
Research shows there is an age-related decline in fertility. The decrease usually starts at the age of 32, with a dramatic fall after the age of 37. The natural monthly fertility rate is about 25% between 20 and 30 years of age. This decreases to below 10% above the age of 35.
A study of nearly 2,200 patients examined women’s fertility using donor sperm. Researchers found that after age 30, fertility declined. After 12 cycles of insemination, 73% were successful for participants under the age of 31, 61% for 31-35 years old, and 54% for those over 35. We see similar trends in women using assisted reproductive technology to get pregnant. Data shows the percentage of IVF cycle starts that result in live births declines after 35. Up until 35, 41.5% are successful, which decreases to 31.9% from 35–37 to 22.1% from 38–40 years, 12.4% from 41–42 years, 5% from 43–44 years, and 1% over 44.
Likelihood of Twins Or Multiples
While fertility may decline with age, your chance of having multiples increases. Twins or multiples are more common with fertility treatments, but there is evidence that multiples are still more common among older women who are not undergoing fertility treatments or IVF. A study found that follicle-stimulating hormone increases with age, which can lead to your ovaries releasing more than one egg. The paradox of declining fertility but increasing twin rates with advancing maternal age is interesting to look at this through the lens of evolution. It would make sense that as you get older and your fertility declines, you release more eggs to have as many children as possible while you still can.
Insulin sensitivity declines with age, and diabetes is more common in older women. Pre-existing diabetes occurs in .4% of 18-34-year-olds, .7% of 35-40-year-olds, and 1% of women over 40.
Gestational diabetes occurs in 1% of 18-34-year-olds, 2.85% of 35-40-year-olds, and 4.86% of women over 40. Although gestational diabetes is more common in older expecting mothers, the rates are still low overall.
High Blood Pressure and Preeclampsia
Similar to diabetes, older women generally have higher rates of high blood pressure, which occurs in 4.7% of 18-34 year-olds, 7% of 35-40 year-olds, and 8% of women over 40. Preeclampsia, characterized by high blood pressure during pregnancy, occurs in relatively the same ratio across all age groups at about 0.75%.
Premature And Low Birth Weight Babies
Babies born with a low birth weight have more respiratory, cognitive, and neurological problems than those born with normal birth weight. Preterm babies have higher risks of heart defects, lung disorders, cerebral palsy, and delayed development. These are both outcomes we would like to avoid.
A study examining these outcomes and maternal age showed a U-shaped association with maternal age. That means low birth weight and preterm birth were more common with younger mothers and older mothers, and rates were lower for mothers in the middle. Expecting women 40 years or older had the highest prevalence of low birth weight babies and preterm deliveries. This study also compared siblings born to the same mother. The researchers found that being over age 35 was not associated with an increased risk of low birth weight or preterm delivery. Another study noted that the risk of preterm birth increased slightly with age and occurred in 6% of 18-34-year-olds, 6.63% of 35-39-year-olds, and 8.17% of women over 40.
According to CDC data, cesarean birth increases with advancing maternal age. Women aged 40 and over were more than twice as likely to deliver by cesarean as women under age 20.
In one study, the rate of emergency cesarean was 8.65% of women ages 18-34, 11.05% of women 34-39, and 14.24% of women over 40. Elective cesarean accounted for 4.37% of women ages 18-34, 8.6% of women 34-39, and 12.67% of women over 40.
Keep in mind that there are a lot of factors that can increase rates of cesarean birth. One is having a breech baby. A breech presentation occurred in 2.61% of women ages 18-34, 3.66% of women 34-39, and 4.57% of women over 40. Another is a previous cesarean delivery. While a vaginal birth after a cesarean may be possible, a cesarean is more likely if you had a previous cesarean. Many mothers giving birth after 35 are not first-time mothers. Remember, nearly one in three babies is born via cesarean.
Lastly, practitioners and their view of the risks associated with an older mother will also play a role in cesarean rates. Keep in mind that there are a lot of contributing factors here.
The technical term for a chromosomal abnormality is aneuploidy. A chromosome abnormality happens when a baby is born with a change in the number or structure of their chromosomes. Down syndrome (also known as Trisomy 21) is the most common chromosome abnormality, and this occurs when there is an extra copy of chromosome 21. According to ACOG, the risk of having a baby with down syndrome is 1 in 1,480 at age 20; 1 in 940 at 30; 1 in 353 at age 35; and 1 in 85 at age 40.
A study of over 15,000 expecting mothers ranging from 19 years old to 52 found that chromosomal abnormalities increased exponentially with maternal age. They looked at the results from a CVS or amniocentesis; these are invasive tests to check for chromosomal abnormalities. Trisomy 21, which is Down’s Syndrome, showed an incidence rate of 11.34 out of 1,000 cases at the age of 35, 15.41 cases at the age of 40, and 37.04 cases at the age of 45. Trisomy 18, also known as Edward’s Syndrome, showed an incidence rate of 1.89 out of 1,000 cases at the age of 35 years, 5.14 cases at the age of 40, and 37.04 cases at the age of 45.
If you are over 35, that statistically increases your risk for a chromosomal abnormality, and your care provider will likely offer additional testing options. Genetic testing starts with a non-invasive screening test to detect risk, and that can indicate the need for an invasive test to diagnose a condition. Be sure to discuss the risks and benefits of any tests with your doctor or midwife, as well as your options and the timing of when specific tests are available. Many of these tests have a particular window of opportunity for the most accurate results. See this episode for Your Guide to Prenatal Testing.
Miscarriage and Stillbirth
A study based on Danish health registries had a huge sample size of over 1.2 million pregnancies. When examining maternal age and fetal loss, they found more than one-fifth of all pregnancies in 35-year-old women resulted in fetal loss, and at 42 years of age, more than half of the intended pregnancies (54.5%) resulted in fetal loss. Fetal loss included miscarriage, ectopic pregnancy, or stillbirth. Miscarriage accounted for 80% of fetal losses. I know those numbers are huge. To put those numbers into perspective, the percentage of miscarriages in the 25-29 age group was 8.14%. This increased to 9.53% from 30-34 to 12.1% in 35-39 year-olds, 15.76% in 40-44-year-olds, and 27.29% in women over 45.
A systematic review of women over 35 found higher stillbirth rates in women aged 35 or older and that risk increases with older ages. Another systematic review that included 37 studies examined maternal age and stillbirth found more than 80% of the studies demonstrated a statistically significant increase in the risk of stillbirth among women over the age of 35. However, the absolute increase in risk was relatively small in studies from developed countries, with crude odds ratios varying from 1.20 to 2.23 on top of baseline stillbirth rates ranging from 1.55 to 17.89 per 1000 total births. To look at the extreme side of this, if the baseline stillbirth rate is 17.89 per 1,000 births, with an odds ratio of 2.23, meaning older women (which was not consistent across all studies) were 2.23 times more likely to have a stillbirth, that would still be a pretty low number. Another study found stillbirth in .47% of 18-34-year-olds, .61% of 35-39-year-olds, and 0.81% of women over 40.
All of these stats on stillbirth can be a little mind-numbing. Stillbirth is one of the stats constantly thrown around when you hear about getting pregnant or having a baby after your 35th birthday, and I want to put it into perspective. Are you at an increased risk if you are over 35? Yes. Please keep in mind that the actual risk, even if you are in your late thirties or your forties, is still low overall. I don’t want you to think that the majority of older women are having stillbirths. The majority of older women have healthy babies.
Limiting Your Risks
You can take many steps at any age to make yourself and your baby as healthy as possible during your pregnancy and reduce your risk of potential complications.
The more you can do to improve your overall health, the better. This includes being at a healthy weight before getting pregnant, eating healthy whole foods, drinking plenty of water, and ensuring you stay hydrated. Prioritizing activities like getting adequate sleep, regular exercise, and physical activity can benefit your health. One of the easiest things you can do is to take a high-quality prenatal vitamin. Anything you do to keep yourself healthy will help you and your baby during pregnancy and birth. This is true whether you are 28 or 38.
Benefits of Being an Older Mother
There is never a time when everything in your life will align to have a baby at the perfect moment. I support you being pregnant at any age, especially if you are over 35. Although some risks increase, being an older mother has many benefits.
A review of pregnancy in women over 35 years of age found that being well-prepared for pregnancy seemed to be a characteristic more typical of older pregnant women. This is because being considered “at risk” causes women anxiety, which they try to ease by preparing themselves for pregnancy and seeking information. By listening to this podcast, you will be well-prepared regardless of your age. Not everyone pregnant is willing to do the work to get educated.
The more life experience you have should translate into you being wiser. As we age, we tend to be more patient, which can be a tremendous benefit as a new parent. A study found older maternal age was associated with less frequent use of verbal and physical sanctions toward children and fewer behavioral, social, and emotional difficulties in children.
Being an older parent may mean a longer life span. Research shows that women who had their last child after 33 were twice as likely to live to the age of 95 as women who had their last child before they reached 30.
If you have kids later, you may have more time to build your career before becoming a parent. This can lead to higher income and more financial stability. This can reduce financial stress with having a baby, possibly allow you to take more time off if you can afford it, and give you more financial resources.
Breastfeeding rates tend to be higher in older mothers. Younger mothers aged 20 to 29 are less likely to breastfeed (79.9%) than mothers aged 30 years or older (84.9%). There is so much you can do to prepare for breastfeeding during pregnancy. See this page for all of the Pregnancy Podcast breastfeeding resources.
A study in Sweden found that having a baby at an older age is associated with positive long-term outcomes for children. Researchers found that individuals born to older mothers, including those at the oldest ages, are taller, remain longer in the educational system, are more likely to attend university, and perform better on standardized tests than their siblings born when their mothers were younger. Part of this has to do with trends in improving health and education overall. For example, a woman born in 1960 with a child at age 20 would have given birth in 1980. If the same woman had chosen to have a child at age 40, that child would have been born in 2000. A lot changed over those 20 years.
Keeping Everything in Perspective
The big takeaway from this article is that while there are some increased risks for getting pregnant over the age of 35, most women having babies in their 30s, 40s, and even early fifties, are having healthy babies. Rather than panicking or stressing out about getting pregnant at 35 or older, hopefully, you have a better perspective of the risks. Plus, a better appreciation for the benefits of being an older mother.
Talk to Your Doctor or Midwife
This is a great topic to discuss with your doctor or midwife. If your due date is after your 35th birthday, ask how your age could potentially change the routine prenatal care you receive or the tests that would be available or recommended.
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