Nowadays, more and more women are opting to have children later in life. In 1970, the average American woman could expect to give birth to her first child by age 21. By the year 2000, that age became almost 25. In other countries, average maternal age at first birth is even higher: Japanese women give birth to their first child at age 28, and Swedish women, around age 28.5.
The reason why women are choosing to have children later in life is because they wish to do other things first, such as obtain a degree, find the right partner, or travel. Take the case of Ann Shuman, a registered nurse who had her first child at age 40 and her second child at age 43. “I’ve led a very active life,” says Shuman. “I’ve pursued a graduate degree while working full time and have traveled to more than 20 countries.
I wasn’t ready to start a family until later in life.” Also, with women living well into their 80s and beyond, the need to marry and start a family is not as pressing as it once was. A broader range of opportunities, both career and otherwise, is leading many women to do other things with their lives first prior to starting families.
While Shuman, and others like her, may choose to have children later in life, there are some risks that need to be considered. The incidence of Down’s Syndrome (also called trisomy 21), a congenital disease marked by physical deformation and mental retardation, does increase with increasing maternal age. A baby born to a 40-year-old woman has a 1/100 chance of being diagnosed with Down’s Syndrome, compared with a 1/1100 chance for a woman aged 25-29. And by age 43, as in Shuman’s case, the chance of having a child affected by Down’s Syndrome is 1/50.
Incidences of other chromosomal abnormalities have also been found to increase with increasing maternal age. A baby born to a 30-year-old woman has a 1 in 384 chance of carrying an extra chromosome, a chromosomal fragment, or missing a chromosome altogether. That possibility jumps to 1 in 178 for a woman just 5 years older, and 1 in 63 after another 5 years go by.
While Down’s Syndrome accounts for the most common type of chromosomal abnormality, other well-known abnormalities are Edward’s Syndrome (trisomy 18), and Patau’s Syndrome (trisomy 13). In a recent study, about 64% of fetuses carried by women younger than 35 years of age had a normal chromosome makeup, compared with only 22% of fetuses carried by women older than 35 years.
What causes the rise in these genetic diseases as a function of maternal age? While all the reasons are unknown, the main fault lies with abnormal division of the older ova, or eggs, in a phenomenon called nondisjunction. During nondisjunction, an egg undergoing division will receive either more or less than its fair share of chromosomes. Upon conception, the resulting embryo will contain a greater (or lesser) number of chromosomes than expected, leading to physical deformities, mental retardation, or even death. Older women are much more at risk for nondisjunction, due mostly to the fact that their eggs are also older.
Unlike sperm, which are renewed every 90 days, a woman is born with all the eggs (about 400) she will ever need over her lifetime. Therefore, a 40-year-old woman has 40-year-old eggs. And 40-year-old eggs, unlike 20 or 30-year-old eggs, will have a greater chance of dividing abnormally, or containing inherent genetic mutations.
While these statistics may seem daunting to the older woman who wishes to become a first (or second) -time mother, they should not be used to dissuade her from her goal. The good news is that several genetic tests do exist to screen for embryos containing genetic abnormalities. Amniocentesis, a test performed on the amniotic fluid surrounding the developing fetus, is commonly used to diagnose Down’s Syndrome. Maternal serum screening may also be performed, to determine the presence of proteins associated with diseases such as trisomy 18, Down’s Syndrome, or open neural tube defect. Even ultrasounds may be used to determine if the fetus is at risk for developing intrauterine distress, or some other physical malformation.
Older women who seek to become mothers may also choose to go for preconception counseling. In fact, according to Jill Maura Rabin, M.D. (a clinical associate professor of obstetrics and gynecology), “Preconception counseling is the single most important thing a doctor can provide to maximize a woman’s chances of having a healthy pregnancy and delivery.”6 During preconception counseling, a woman will be asked questions about her and her partner’s genetic background, her health, and her lifestyle.
She will be advised on pre-pregnancy and prenatal nutrition and care. Furthermore, one or more genetic tests may be performed on her, as well as her partner, to determine the chances of conceiving a child that will test positive for various genetic defects. This is especially important if the woman or her partner already carry known genetic predispositions to diseases such as autism, or even diseases which have nothing to do with advanced maternal age, such as Huntington’s Disease.
For women or their partners who do have a strong chance of conceiving a child with a birth defect, one solution is in vitro fertilization (IVF) coupled with embryo selection. This solution may not be ethically suitable for some individuals. However, it is one way to help ensure that the resulting child will not suffer from such inherited diseases as Down’s Syndrome, or other chromosomal abnormalities. IVF also helps ensure that conception takes place, especially in cases where the woman’s partner is also older. Because older men undergo reduced fertility, along with the risk of producing abnormal sperm, it may make sense to collect ova and sperm separately, uniting both in a more reproductively conducive, as well as selective, environment. The in vitro conceived embryos can then be implanted into the woman’s uterus.
Despite the probable success of conception, the road from fertilization to full-term delivery is a long one. The American College of Obstetricians and Gynecologists estimates that 10-25% of clinically recognized and 50-75% of clinically unrecognized (before a missed period) pregnancies end in miscarriage7. Women younger than 35 will miscarry about 15% of the time, while women 35-45 will miscarry 20-35% of the time. Women who are older than 45 years of age are estimated to miscarry up to 50% of the time.
Because miscarriage is often the result of chromosomal abnormalities in the embryo, a pre-selected embryo that is implanted into the older woman may stand a better chance of being carried to full-term delivery. Likewise, miscarriage is often the result of the expectant mother’s lifestyle: obviously, smoking, drinking, and partaking in recreational drugs are not ideal conditions for a successful pregnancy. The older woman, with adequate preparation and care, can actually fare better during her pregnancy than a younger, and less responsible, woman.
Several other factors may plague the older woman during her pregnancy, however. In a study of 24,032 pregnancy outcomes for women aged 40 and over, William Gilbert and his group found that older first time mothers had a fourfold higher incidence of gestational diabetes, a 70% increase in breech birth, an 80% increase in high blood pressure, a 48% increase in inadequate contractile force, and a 30% increase in prolonged labor, compared with their younger counterparts. Even for women who had previously given birth, pregnancy complications were still high.
Most striking was the increase in delivery by Caesarian section for older mothers: regardless of whether the older women had or had not previously given birth, their rate of Caesarian delivery was twofold higher compared with that of women aged 35 years and younger. Older first-time mothers had especially high rates of around 47%, due mostly to complications during either the pregnancy itself, or labor and delivery. Another reason for this higher percentage is the increased incidence of twin babies in older mothers: generally, Caesarian section is the advised method for safe delivery of multiple children.
However, the good news is that, more and more women past the age of 40 are having full-term, healthy babies. In 2003, the Centers for Disease Control and Prevention gathered birth data on women of various ages, and found that an increasing number of women aged 40-44 had given birth, compared with the number from the year before. Furthermore, for the first time ever, births to women aged 40 years and over topped 100,000 for that year.
Overall, the birth rate for women aged 40-44 years has actually doubled since 1981. These data, along with the data gathered by Gilbert and his group, show “that the vast majority of women who delay childbirth until age 40 have babies who are just as healthy as those born to women aged 20 to 29.” Also, “although a variety of complications are increased in the older first-time mother, this information should not deter women from considering pregnancy at an advanced maternal age and should help high-risk obstetricians better counsel and monitor women to produce the best possible results.”
Jacobsson, B., Ladfors, L., and I. Milsom. Advanced Maternal Age and Adverse Perinatal Outcome. Obstetrics & Gynecology. 2004.104:727-733.
First childbirth at age 40 is largely safe, but Caesarean rate is doubled and complications are up as much as tenfold. http://www.ucdmc.ucdavis.edu/news/childbirth40.html
Hook, E.B. Chromosomal abnormality rates at amniocentesis and in live-born infants. Journal of the American Medical Association. 1983. 249:2034-2038.
Schmidt-Sarosi, C. Infertility in the older woman. Clinical Obstetrics and Gynecology. 1998. 41(4): 940-950.
The Cancer Resource Center. http://cancerresourcecenter.com/articles/article33.html
American Pregnancy Association. http://www.americanpregnancy.org/pregnancycomplications/miscarriage.html
Gilbert W.M., Nesbitt T.S, and B. Danielsen. Childbearing Beyond Age 40: Pregnancy Outcome in 24,032 Cases. Obstetrics & Gynecology. 1999. 93:9-14.
Birth Rate for Women Aged 40-44 Years Rose in 2003, New Report Finds. http://www.cdc.gov/nchs/pressroom/04facts/birthrates.htm