The rate of live births among women in the US who are aged 35 and older has risen from five percent of all live births in 1970 to thirteen percent in the year 2000. And this rate continues to rise.
Q: We know that it’s harder to conceive and the risk of miscarriage increases as women get older. Once an “older” woman is successfully pregnant with a single fetus and has been reassured, through multiple tests, that her pregnancy is “okay,” does she or her baby still have significant risks?
A: For decades, doctors have had to rely on small studies in order to answer this question. And many of these studies included women with medical problems, infertility or even multiple pregnancies. A new study just published in the Journal of the American College of Obstetricians and Gynecologists gives us a better understanding as to whether the risks are greater and what these risks are in “normal” women whose only “deviance” is to be pregnant in her late thirties or early forties. Data was collected from 15 maternity centers in the U.S., in which more than 36,000 women who had single pregnancies were followed between 1999 and 2000. The acronym for this study was the First and Second Trimester Evaluation of Risk (FASTER) trial. It was sponsored by the National Institute of Child Health and Human Development.
Seventy-nine percent of the mothers were younger than 35, 17 percent were between 35 and 39 and 4 percent were 40 or older. What made this study unique — and allowed them to help answer the question: “Am I, the pregnancy or my baby at risk just because I’m older?” — is the fact that the researchers gathered information about factors that are known to influence pregnancy outcome. These included weight, ethnicity, education, marital status, smoking, pre-existing medical conditions (such as high blood pressure, diabetes, heart disease), a history of previous pregnancy complications and use of assisted reproductive (fertility) care. They could then adjust or correct for these factors and present pure risk estimates (called adjusted odds ratios) for age alone.
Q: Were the “older” women much different than those under 35?
A: Yes, they were more likely to be white and married and have previous deliveries and were also more likely to be diagnosed before their pregnancy with chronic diabetes and hypertension. Moreover, they were more likely to be taking medication and to have used fertility treatments to achieve their pregnancies. But again, knowing this allowed the statisticians to correct for these differences.
Q: What were the results?
A: First the good news. When compared to younger moms, women over 35 were not at increased risk for:
- High blood pressure during pregnancy, or preeclampsia
- Pre-term labor
- Premature ruptured membranes
- Operative vaginal delivery (forceps or vacuum)
There was a slight increased risk between 35 and 39 for:
- Gestational diabetes
- Low-lying placenta (previa)
- Large baby (macrosomia)
- Cesarian section
There was, however, a greater than one and a half to two times increased risk for women over 40 for:
- Gestational diabetes
- Placenta previa
- Placenta abruption (separation and bleeding)
- Cesarian delivery
- Perinatal mortality (stillbirths and newborn deaths)
Q: What does this mean to women who want to wait to have their children?
A: We are still concerned about waning fertility. As our eggs get older, though they may still provide normal hormonal production and menstrual cycles, they lose their ability to become fertilized or to go on to form the dividing embryonic cells with the chromosomal content necessary for development of a viable embryo and subsequent normal fetus. This loss of reproductive capacity occurs gradually through our early 30s, accelerates in our late 30s and by our 40s quickly becomes a fact that cannot be reversed (without using donor eggs), until we run out of eggs and enter menopause. (Just a few stats: between the ages of 19 and 26, there’s a 50 percent chance of achieving pregnancy in one menstrual cycle when trying. This falls to 40 percent for ages 27 to 34 and 30 percent for women in their late 30s.)
Even if fertilization does take place, the right chromosomal mix and match deteriorates when older eggs are put into the mix. This is the chief reason that miscarriage is much more likely to occur as we get older. The imbalanced chromosomes in the embryo cause it to cease development, after which it aborts (this is a miscarriage) or if it develops, there are subsequent congenital abnormalities and anomalies.
The FASTER study shows this to be the case. Miscarriage rates for ages 35 to 39 increased twofold; and 2.4 times for women over 40. Chromosomal abnormalities increase fourfold in the 35-to-39 group, and 9.9 times in women over 40. Congenital anomalies were 1.2 to 2.4 times more frequent in each group when compared to younger women. (Note that the latter number was lower than that for chromosomal abnormalities because abnormal pregnancies tended to be miscarried, or terminated once a diagnosis was made.)
But this study does show that once women who are 35 to 40 are diagnosed with a “normal,” viable pregnancy, the outcome will generally be favorable. Her baby should deliver at term with a birth weight comparable to infants born to younger women. She is not significantly more likely to bleed, develop hypertension or preeclampsia, have early labor or need an operative vaginal delivery. Maternal age over 40, however, is considered an independent risk factor for developing diabetes during pregnancy and having placental problems and perinatal mortality. This may be due to the damage age may cause to blood vessels supplying the uterus, placenta and pregnancy; they may simply not be able to adequately adapt to the huge blood flow demands of the pregnancy.
The fact that women over 40 are more likely to have a C-section may reflect the fact that an older uterus is less likely to contract efficiently during labor. But it is also quite possible that the patient and her doctor don’t want to take any chances once she has reached the end of her pregnancy and simply opt for a C-section to prevent any possible obstetrical complications.
Q: What does all this mean for obstetrical care in older women?
A: Women between 35 and 40 should definitely get early prenatal care and undergo testing to ascertain that there are no chromosomal abnormalities through specific blood tests, ultrasounds, chorionic villous sampling (CVS) and/or amniocentesis. Once a woman is 40 or older, she also needs to be closely monitored for pregnancy complications. She should have more frequent ultrasounds and fetal monitoring, especially in the last trimester of pregnancy. It is highly advisable that she seek care with an obstetrician who is competent in handling high (or higher) risk pregnancies.
Dr. Reichman’s Bottom Line: With the right care, most women can have healthy babies, even at a later age.
Dr. Judith Reichman, the “Today” show's medical contributor on women's health, has practiced obstetrics and gynecology for more than 20 years. You will find many answers to your questions in her latest book, "Slow Your Clock Down: The Complete Guide to a Healthy, Younger You," published by William Morrow, a division of .
PLEASE NOTE: The information in this column should not be construed as providing specific medical advice, but rather to offer readers information to better understand their lives and health. It is not intended to provide an alternative to professional treatment or to replace the services of a physician.