By Eleanor Mayfield
It’s a trend many Americans are seeing firsthand among their family members and friends, and it’s supported by government data: more women are delaying having children until they reach their thirties or forties.
In 2012 birth rates for women in their thirties and forties rose even as they dropped for women in their twenties and reached a historic low for teenagers,1 continuing a two-decade trend: between 1990 and 2008, pregnancy rates declined for women in all US demographic groups except those in their thirties and forties.2 About 40 percent of all babies in the United States are now born to women over 30, and almost 15 percent-—one in seven—are born to women 35 and older.1
Experts in fertility and reproduction intensely debate the pros and cons of this trend. But what are the facts? What should women 30 and older who are contemplating pregnancy know and expect?
Getting Pregnant: Fertility after Age 30
Every woman has the most oocytes (immature egg cells) she will ever have before she is even born: At 20 weeks’ gestation, a female fetus has 6 to 7 million oocytes; at birth, 1 to 2 million. By the time she has her first period, she has about 250,000 left; by age 37, about 25,000.3
As a woman gets older, her egg cells are more likely to have genetic abnormalities such as too many or too few chromosomes. (The normal number is 23; when an egg is fertilized by a sperm that also has 23 chromosomes, the resulting embryo will have the normal complement of 46.) Most of the time, when an embryo has a chromosomal abnormality, pregnancy either doesn’t occur or the woman has an early miscarriage.
At age 30 a healthy, fertile woman has a 20 percent chance of getting pregnant each month that she tries, according to the American Society for Reproductive Medicine. By age 40 that chance is less than 5 percent per monthly cycle.4
But the rate at which fertility declines differs from one woman to another, for reasons not clearly understood.
“Some women can get pregnant at age 40 and some women can’t—and we really don’t know why,” says Anne Z. Steiner, MD, MPH, associate professor of reproductive endocrinology and infertility at the University of North Carolina School of Medicine in Chapel Hill.
Dr. Steiner directs Time to Conceive, a research study involving 750 women ages 30 to 44 that is seeking to identify hormonal and other factors affecting the ability of women in this age group to get pregnant. Preliminary findings from Time to Conceive suggest that possible differences in the rate of fertility decline between women who have gotten pregnant before age 30 and those trying to get pregnant for the first time after that age.
“Among healthy, nonobese women ages 30 to 44 who have been pregnant before, we’re not seeing large declines in fertility until age 40,” Dr. Steiner explains. “By contrast, in the group that has never been pregnant before, we start to see a significant drop-off in fertility at age 34 or 35.”
Dr. Steiner says she advises patients in their early thirties who are concerned about declining fertility that “they have a few years before they need to worry. For women who come to me at 35 who have never been pregnant, my advice is they need to start thinking about trying to get pregnant in the next six months.”
“The optimal age range for childbearing is probably between 20 and 34,” says Kiran B. Tam Tam, MBBS, MS, assistant professor of obstetrics and gynecology at Baylor College of Medicine in Houston. At 35 or older, the statistical risk of a range of pregnancy complications begins to increase (see sidebar “Possible Pregnancy Complications in Older Mothers”).
Importance of Preconception Care
The best time to begin addressing pregnancy risks in an older mother is before she gets pregnant, says Rebecca L. Shiffman, MD, a maternal/fetal medicine specialist at Woodhull Medical Center in Brooklyn, New York.
“A woman who is in really good health and physical shape before she gets pregnant is more likely to have a healthy pregnancy,” says Dr. Shiffman. “I always say that the first prenatal visit should be before conception.”
Ensuring a Safe and Healthy Pregnancy at Age 30 and Older
As with women who get pregnant before they are 30, women who are over 30 can take proactive steps to ensure a healthy pregnancy.
Before Getting Pregnant
- Choose an obstetrician-gynecologist with whom you feel comfortable and who has experience with pregnancies in women over 30.
- If you or your partner smokes, stop. Smoking makes it harder to get pregnant. If you do get pregnant, smoking increases the risk of a miscarriage and of the baby’s being born too early, having a low birth weight, or having a birth defect such as a cleft palate.
- If you are overweight, try to shed those extra pounds. Like smoking, being overweight makes it harder to get pregnant. If you do get pregnant, those extra pounds will increase your risk of a long list of pregnancy complications.
- See your doctor for a physical exam.
- Get checked for high blood pressure and diabetes. If you have either condition, consider holding off trying to get pregnant until it is well controlled.
- If you have already been diagnosed with high blood pressure or diabetes, talk with your doctor about the medications you are taking. Your doctor may recommend switching to medications that are safer to take during pregnancy.
- Consider seeing a genetic counselor to assess your family history and risk of passing on a genetic condition.
- Keep all of your appointments for prenatal care.
- Eat a healthy diet and get regular exercise.
- Take a prenatal vitamin and a folic acid supplement daily.
- Avoid alcohol and illegal drugs.
- Talk with your doctor before taking any prescription or over-the-counter medications.
- Talk with your doctor about noninvasive prenatal testing (see sidebar “Noninvasive Prenatal Testing Becomes a Reality”).
- Consider being tested with either chorionic villus sampling or amniocentesis for genetic conditions, including Down syndrome, in the fetus (see sidebar “Screening for Genetic Disorders”).
- Consider an ultrasound fetal anatomy survey at about 20 weeks to check for physical abnormalities in the fetus.
The Good News
- Although women who postpone childbearing until age 30 or older may face more complications than do younger women both in getting pregnant and during pregnancy, some research suggests that later motherhood may offer benefits for both mothers and children.
- Children up to age five born to 40-year-old mothers had fewer unintentional injuries, better language development, and fewer social and emotional difficulties than children the same age born to younger mothers.5
- Children ages three to 10 born to mothers 30 and older were taller and slimmer than those of younger mothers.6
- Women who had children at age 35 or older were happier long-term than women who had children earlier in life.7
1. Hamilton BE, Martin JA, Ventura SJ. Births: Preliminary data for 2012. US Centers for Disease Control website. Available at http://www.cdc.gov/nchs/data/nvsr/nvsr62/nvsr62_03.pdf. Accessed October 3, 2013.
2. Ventura SJ, Curtin SC, Abma JC, Henshaw SK. Estimated pregnancy rates and rates of pregnancy outcomes for the United States, 1990–2008. US Centers for Disease Control website. Available at http://www.cdc.gov/nchs/data/nvsr/nvsr60/nvsr60_07.pdf. Accessed October 3, 2013.
3. Balasch J, Gratacós E. Delayed childbearing: effects on fertility and the outcome of pregnancy. Fetal Diagnosis and Therapy. 2011;29(4):263-73. doi: 10.1159/000323142.
4. American Society for Reproductive Medicine. Age and Fertility: A Guide for Patients. Available at http://www.asrm.org/uploadedFiles/ASRM_Content/Resources/Patient_Resources/Fact_Sheets_and_Info_Booklets/agefertility.pdf. Accessed October 3, 2013.
5. Sutcliffe AG, Barnes J, Belsky J, Gardiner J, Melhuish E. The health and development of children born to older mothers in the United Kingdom: observational study using longitudinal cohort data. BMJ 2012;345:e5116. doi: 10.1136/bmj.e5116.
6. Savage T, Derraik JGB, Miles HL, Mouat F, Hofman PL, Cutfield WS. Increasing maternal age is associated with taller stature and reduced abdominal fat in their children. PLoS ONE 8(3):e58869. doi:10.1371/journal.pone.0058869.
7. Myrskylä M, Margolis R. Happiness: before and after the kids. 2012. Rostock, Germany: Max Planck Institute for Demographic Research. MPIDR working paper WP 2012-013. Available at http://www.demogr.mpg.de/papers/working/wp-2012-013.pdf#search=%22wp%202012-013%22. Accessed October 3, 2013.
8. American College of Obstetricians and Gynecologists Committee on Genetics and The Society for Maternal-Fetal Medicine Publications Committee. Noninvasive Prenatal Testing for Fetal Aneuploidy. Committee Opinion Number 545. December 2012. Available at http://www.acog.org/Resources_And_Publications/Committee_Opinions/Committee_on_Genetics/Noninvasive_Prenatal_Testing_for_Fetal_Aneuploidy. Accessed October 4, 2013.
9. Devers PL, Cronister A, Ormond KE, Facio F, Brasington CK, Flodman P. Noninvasive prenatal testing/noninvasive prenatal diagnosis: the position of the National Society of Genetic Counselors. Journal of Genetic Counseling. 2013;22(3):291-95.
One Woman’s Story: A First-Time Mother at 46
When Cherrill Spencer of Palo Alto, California, married at age 40, it was a first marriage for both her and her husband, Rick. Neither had children and both, she says, were “on the fence” about doing so. Both scientists, they knew about the increased risk of birth defects in children born to older mothers. Cherrill also knew that women her age had an elevated risk of miscarriage and that the odds of getting pregnant at all might be against her.
On the plus side, apart from periodic back pain caused by a degenerated vertebral disc, her general health was good—she had never smoked, did not drink alcohol, was not overweight, and did not have high blood pressure or diabetes.
When the couple decided to try for a pregnancy, they set about it methodically. Cherrill took her temperature every morning to check when she was close to ovulating. (Basal body temperature rises by about half a degree when the ovaries release an egg.) “My periods had always been regular, so that helped,” she says.
After about seven months, she had a positive pregnancy test but miscarried a few weeks later. Then, inexplicably, she came down with chickenpox. The couple was advised to wait a while before trying again. Cherrill’s second pregnancy ended in another early miscarriage, and they had to wait a few more months. That summer she took Clomid® (clomiphene), an oral fertility drug that stimulates ovulation. In late October she got pregnant again.
“Third time lucky,” she says. She was now 45. At the childbirth classes she and Rick attended, “all the women were 15 to 20 years younger than me, but many of them were having a worse time in pregnancy than I was. I had some morning sickness but not that much. I had less back pain than I did before I was pregnant.”
She attended all of her prenatal care appointments and took the vitamin and folic acid supplements her obstetrician-gynecologist recommended. At about 10 weeks, she underwent chorionic villus sampling, a test to diagnose genetic abnormalities in the fetus. The results revealed no abnormalities.
Although preterm labor and delivery is another risk that older mothers face, Cherrill’s baby wasn’t in a hurry. A healthy girl weighing 6 pounds, 15 ounces, she was born about a week after her due date and four and a half months after her mother’s forty-sixth birthday.
That was in August 1994. Cherrill and Rick’s daughter, Sierra, is now 19 and a sophomore in college.
In the years since her own late pregnancy, Cherrill says she has talked to many women, other scientists, who have reached their midthirties without having children and are worried that it might be too late. “I point to my own experience to show it can be done.”
Screening for Genetic Disorders: Guidelines Now Focus on Risk, Not Age
Amniocentesis (amnio) and chorionic villus sampling (CVS) are prenatal diagnostic tests to identify genetic disorders. Best known as tests for Down syndrome, they can also detect many other disorders caused by chromosomal abnormalities. Both tests involve using a needle to draw fluid from the amniotic sac (amnio) or villi from the placenta (CVS). Amnio is usually performed during or after the fifteenth week of pregnancy; CVS, between the tenth and twelfth weeks. Women who opt for the testing undergo one test or the other, not both. Both tests carry a small risk of inducing a miscarriage.
Since the 1970s doctors have routinely offered these tests to pregnant women ages 35 and older, who are at higher risk than younger women of having a baby with a genetic disorder. Thirty-five became the cutoff because at that age the risk of the procedure’s inducing a miscarriage was deemed about equal to the risk of having a baby with Down syndrome.
Recommendations for who should be offered screening with amnio or CVS changed in 2007. The new guidelines abolished the age 35 cutoff and recommended that doctors first offer less-invasive blood or ultrasound tests to screen all pregnant women, regardless of age, for genetic disorders. Women whose test results signal an increased risk of having a baby with Down syndrome or other genetic disorder should then be offered genetic counseling and the option to undergo either amnio or CVS.
Amnio and CVS remain the “gold standard” tests for detecting genetic disorders, although noninvasive prenatal tests are becoming popular options (see sidebar “Noninvasive Prenatal Testing Becomes a Reality”).
|Birth defects||Women 35 and older are more likely to have children with a birth defect caused by a chromosomal abnormality, such as Down syndrome.|
|Cesarean delivery||The likelihood of having a cesarean delivery is roughly doubled for women over 35; this has been attributed to an increase in medical complications, fetal abnormalities, and length of labor.|
|Diabetes||Women 35 and older are more likely than younger women to have diabetes before pregnancy. They also have a higher risk of developing diabetes during pregnancy (gestational diabetes), especially if they are overweight. Women with diabetes may have very large babies (weighing more than 9 pounds at birth), which can make for a difficult labor, an elevated need for cesarean delivery, and a risk of injury during delivery.|
|High blood pressure||Women 35 and older are more likely to have elevated blood pressure (chronic hypertension) before pregnancy. They are also at higher risk of preeclampsia, a condition associated with elevated blood pressure that occurs only during pregnancy. High blood pressure may reduce blood flow to the placenta, so the fetus receives less oxygen and fewer nutrients. This can result in restricted growth or slower development of the fetus.|
|Miscarriage||Older mothers are at higher risk of having a fetus with a chromosomal abnormality, which increases the risk of a spontaneous miscarriage.|
|Multiple pregnancy||As women get older, hormonal surges can result in more than one egg being released during ovulation, increasing the chance of a multiple pregnancy. Women who have multiple pregnancies have a higher risk of gestational diabetes, preeclampsia, and preterm birth.|
|Preterm birth||Older mothers have a higher risk of preterm birth (delivery before 37 weeks of pregnancy). Preterm babies may require weeks or months of intensive care and may have a variety of lifelong health problems.|
|Stillbirth||Older mothers are at increased risk of stillbirth, a risk that peaks in the final weeks of pregnancy. Doctors may recommend monitoring the baby and early delivery if they are concerned about the possibility of stillbirth.|
American Congress of Obstetricians and Gynecologists, acog.org/For_Patients
ReproductiveFacts.org, reproductivefacts.org; resources for patients about fertility, infertility, and other issues related to reproduction from the American Society for Reproductive Medicine
Elizabeth Gregory, Ready: Why Women Are Embracing the New Later Motherhood (Basic Books, 2012)
Noninvasive Prenatal Testing
Becomes a Reality By Kari Bohlke, ScD
Since the 1970s pregnant women have had the option of being tested for chromosomal abnormalities in the fetus (such as trisomy 21, also known as Down syndrome). Screening typically involves blood tests and ultrasound; if these tests—which have somewhat limited accuracy—produce an abnormal finding, women often proceed to invasive testing with amniocentesis or chorionic villus sampling for a definitive diagnosis. Risks of invasive testing include a small chance of miscarriage, but the need for invasive testing may be substantially reduced by a new generation of prenatal tests.
Noninvasive prenatal testing (NIPT) is a new approach to screening for trisomies of chromosomes (three copies) that involves evaluation of fetal DNA collected from the mother’s blood. The first tests to hit the market rely on “cell-free DNA,” which are fragments of fetal genetic material that circulate in maternal blood during pregnancy. These fragments do not last for long in the mother’s blood and provide information about the current pregnancy only. An advantage of this type of testing is that it provides more-accurate information than standard blood tests about aneuploidies, an abnormal number of chromosomes, such as three copies of chromosome 21 instead of the normal two copies.
Optimal use of these tests is still being explored, but they may be used as a follow-up to abnormal results on standard blood and ultrasound tests or as an initial screening tool. Due to the lower number of false-positive test results, they have reduced the need for invasive, diagnostic testing for aneuploidies of whole chromosomes. Women who receive an abnormal result based on cell-free DNA, however, are still referred for invasive testing to confirm the result (NIPT is currently a screening test only, not a diagnostic test). The cell-free DNA assays test for only about one-third of the possible chromosome abnormalities.
Another type of NIPT that is expected to become available in the next year or two analyzes the DNA from intact fetal cells (specifically, fetal nucleated red blood cells). Like cell-free DNA fragments, these cells circulate in maternal blood and have a limited life span. In contrast to cell-free DNA fragments, however, intact cells contain the fetus’s entire genome; this would make it possible to test for a much broader range of genetic abnormalities. Furthermore, because these cells come from the fetus itself, rather than from the placenta, as most cell-free DNA fragments do, it avoids the potential problem of confined placental mosaicism, a situation in which the chromosomal makeup of the placenta differs from that of the fetus.
Currently, the American Congress of Obstetricians and Gynecologists recommends offering NIPT as part of screening for women who are at increased risk of having a fetus with certain chromosomal abnormalities.8 Women should be counseled carefully, however, so that they understand that most of the risk of genetic abnormalities remains even after such screening. There is still limited information about how these tests perform in low-risk pregnancies. The National Society of Genetic Counselors also supports NIPT as an option when there is an increased risk of a chromosomal abnormality, and it stresses the importance of informed consent, education, and counseling by a qualified provider, such as a certified genetic counselor.9
As prenatal testing continues to evolve, it is likely to raise some difficult questions for families and physicians. Women will have the option of receiving ever-expanding information about their pregnancy but will need to think carefully about the types of information that they actually want. These decisions are extremely personal, and they highlight the importance of education and counseling both before and after testing. When women want to receive a particular piece of information, however, the ability to receive it early, accurately, and noninvasively is an important advance.
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