Being pregnant and over 35 Home > Education
Being pregnant and over 35
More women today tend to put off having a baby until their careers are well established or until they have gained more life experiences. Local and worldwide statistics have shown that since the 1970's, birth rates for women in their late 30's and 40's have increased dramatically. Advances in medical care have enabled the older women to have safer pregnancies than in the past. Although the risks are increased, most women over the age of 35 have healthy pregnancies and healthy babies. However, women should be aware of the risks associated with later childbearing so that they can make informed decisions about their pregnancies.
Age and Fertility
A woman's fertility peaks at ages 20 to 24 and remains constant through the early 30's, after which it begins to decline. At 30-35 years, fertility drops 15-20% below the maximum. From ages 35 to 40, the decrease is 25-50% and 50-95% beyond 40 years.
The decrease in fertility may be (in part) due to the decline in ovulation, a decrease in the frequency of intercourse and the presence of medical and gynaecological conditions such as endometriosis which interferes with conception.
If conception does not occur after six months of trying, a woman over 35 should seek medical help. It has been shown that about one-third of women between 35 and 39, and up to two-thirds of women over 40 have problems conceiving. However, many of these cases can be treated successfully.
What are the potential risks in pregnancy and childbirth for an older mother?
Complications in pregnancy for the older mother are often exaggerated. Although the pregnancy rates over the age of 35 has nearly doubled, the risks associated with pregnancy increases gradually as age advances.
Risks to the mother:
  • Chronic health problems, such as diabetes and high blood pressure, are more common in older women. These conditions should be under control well before conception and careful medical monitoring throughout pregnancy would reduce the associated risks.
  • High blood pressure and diabetes can develop for the first time in pregnancy, especially in women above the age of 35. Regular and frequent antenatal care will allow early diagnosis and treatment of such conditions.
  • There is an increased risk of placental problems. Placenta praevia (low lying placenta) is eight times more common in the older mother, and necessitates delivery by caesarean section.
  • Older mothers are more likely to have problems with labour and delivery. Fetal distress and prolonged labour are more common. The risk of caesarean section can be as high as 43% in those over the age of 35 years.
Risks to mother Risks to baby
High blood pressure & diabetes Increased miscarriage
Placenta praevia (low lying placenta) Increased chromosome disorders
Premature delivery Stillbirths
Caesarean delivery Fetal distress in labour
Low birthweight
Risks to the baby:
  • Most miscarriages occur in the first trimester of pregnancy. The rate of miscarriages is increased significantly in older women. The risk is 9% for women aged 20 to 24, rising to 20% at age 35 to 39 and more than 50% by the age of 42.
  • As a woman ages, the risk of bearing a child with a chromosomal defect increases. The most common is Down syndrome, where there is an extra chromosome 21, giving a total of 47 chromosomes (the normal being 23 pairs or 46 chromosomes). A child with Down syndrome is usually mentally sub-normal and may suffer physical abnormalities. The risk of Down syndrome at 25 is about 1-in-1,250, rising gradually to 1-in-1000 at 30, 1-in-400 at 35. This rise becomes more significant at age 40 (1-in-100) and even higher at 45 (1-in-30). Similarly, there is an increased risk of other less common chromosomal defects such as Edward syndrome (an extra chromosome 18) and Patau syndrome (an extra chromosome 13) with increasing age.
Age Mother (years) Risk of Trisomy 21
20 1 in 1667
30 1 in 952
35 1 in 385
37 1 in 227
40 1 in 106
43 1 in 50
45 1 in 30
Reference: Hook EB. Rates of chromosomal abnormalities at different maternal ages. Obstetrics and Gynecology, 1981;58:282-285 and Hook EB, Cross PK and Schreinemachers DM. Chromosome abnormality rates at amniocentesis and in liveborn infants. Journal of the American Medical Association, 1983;249:2034-2038
Women over the age of 35 are 20-40% more likely to have a low birth-weight baby and 20% more likely to have premature delivery. There is also an increased risk of stillbirths.
How can I reduce my risks and increase the chances of having a healthy baby?
Good health before and during pregnancy will minimize the risk of complications. Here are some recommendations for pregnancies after 35.
  1. Plan for the pregnancy. See your doctor before you conceive. Medical conditions can be stabilized. Medications and immunizations can be reviewed and modified if necessary.
  2. Take a daily multi-vitamin, including folic acid. Start before you conceive until the first 12 weeks of pregnancy. 400 mcg daily will prevent neural tube defects. Daily intake of multi-vitamins has recently been shown to prevent other birth defects such as congenital heart defects.
  3. Maintain a healthy and well-balanced diet. Eat a variety of nutritious foods.
  4. Exercise regularly. Review your exercise program with your doctor. You may continue to exercise during your pregnancy but the regimen may have to be modified.
  5. Be of the correct weight (*BMI 18.5 -22.9); do not be overweight (BMI > 23) or underweight (BMI < 18.5)
  6. Do not drink alcohol and do not smoke. Do not use any medication unless recommended by your doctor. Do not take herbal supplements, natural products without first checking with your doctor.
  7. Ensure that you obtain early antenatal care. See your doctor as soon as you become pregnant.
*BMI = Body Mass Index = weight (kg) / height (m2). Values quoted are Asian BMI values.
Tips for a healthy pregnancy after 35
a) eat healthy food
b) maintain an ideal weight
c) exercise regularly
d) pre-pregnancy and early antenatal check-ups
e) take daily multi-vitamins and folic acid
f) avoid smoking, alcohol and drugs
The first 8 weeks of pregnancy are critical in the baby's development. Early and regular antenatal care will optimize the pregnancy outcome. In addition, good antenatal care includes education on pregnancy and childbirth, counseling and support.
Antenatal tests for Pregnancy after 35
Antenatal tests aim to monitor the health of the mother and her baby. Some tests are done routinely while other tests are offered to some women because of their age. There are two kinds of antenatal tests; the screening and diagnostic tests. Screening tests are designed to screen a large population of women to identify those who have a higher-than-average risk of a particular disorder or defect. Diagnostic tests usually confirm if there was an abnormality. They are used to determine whether there is in fact a problem with the pregnancy.
Women over 35 are offered various tests, some of which require genetic counseling, including a detailed discussion on the risks and benefits of each test. This is important, as you will be required to make informed decision on various kinds of tests.
Screening tests Diagnostic tests
Ultrasound scan Amniocentesis
Maternal serum biochemistry Chorionic villous sampling
Ultrasound scan:
This utilizes high frequency sound waves to produce an image of the baby on a monitor/screen. Ultrasound is used in early pregnancy to determine viability (to ensure the baby is in the womb and if there is fetal heart movement). It will detect multiple pregnancies and determine the gestational age to confirm the estimated date of delivery (EDD). In later pregnancy, ultrasound is used to assess the health of the baby by estimating the fetal weight (growth) and amount of amniotic fluid around the baby. Doppler ultrasound is used to assess the blood flow through the umbilical cord and fetal vessels to check if the baby is healthy.
Older women have an increased risk of chromosomal disorder in the baby. The "nuchal scan" (11 to 13+6 weeks), is used to screen for Down syndrome. Nuchal translucency (NT) measures the area beneath the skin of the fetal neck. An increased in NT measurement increases the risk of Down syndrome and cardiac abnormalities in the fetus. Using this parameter, 83% of Down syndrome can be detected. The sensitivity or detection rate can be further improved to almost 90% by looking for the presence of the nasal bone in the fetus. The ultrasound scan is therefore the most sensitive screening test for Down syndrome but it must be done within this "window period", 11-13+6 weeks (CRL or crown-rump-length 45 to 84 mm).
Nuchal translucency measurement
The detection rate of chromosomal disorders such as Down syndrome after the 14th week is only about 30%. This is because only about 30% of such fetuses have structural abnormalities (major or minor markers) which can be seen on ultrasound scan such as cleft lip, ventriculomegaly (excess fluid in the brain) or cardiac defects (hole in the heart). The detailed scan performed at 20 weeks will detect most structural defects in the baby, some of which are associated with a chromosomal disorder. Some examples include spina bifida, omphalocele (protrusion of abdominal contents such as liver and gut through an anterior abdominal wall defect) and diaphragmatic hernia.
Maternal serum biochemistry
Blood is taken from mothers in the first trimester (11-13+6 weeks) or in the second trimester (about 16 weeks), to measure different substances or chemicals. The first trimester measures PAPP-A (Pregnancy Associated Plasma Protein-A) and free b-hCG (Beta Human Chorionic Gonadotrophin). This blood test detects 68% of Down syndrome and 90% of Edward syndrome. When combined with the NT measurement, almost 95% of Down syndrome can be detected.
In the second trimester, blood is taken for the double test, triple test or quadruple test, depending on the number of substances or chemicals measured. Measurement of a-FP (Alpha Feto-Protein) and unconjugated oestriol (uE3) constitute the "double test". Additional measurement of free b-hCG (Beta Human Chorionic Gonadotrophin) is the "triple test" and further measurement of Inhibin-A, forms the "quadruple test". The increasing number of substances measured, increases the sensitivity or detection rate. However, using this second trimester test, the detection rate of Down syndrome, at best, is about 68%.
The report will first indicate the age related risk such as 1-in-300 at 36 or 1-in-100 at 40. Each laboratory will have a cut-off point, usually at 1-in-250 or 300. The substances are measured, computed and calculated. Using the cut-off point for the laboratory, the results are either "positive" or "negative". If the risk calculation is 1-in-400, it becomes a negative screen. However, if the risk is calculated as 1-in-200, it is a positive screen. A positive result does not mean that the baby has Down syndrome but an amniocentesis is recommended to confirm any chromosomal defect. Hence, a 40 year old (assuming an age related risk of Down syndrome 1-in-100) will be reassured with this result as she is four times less likely to have a baby with Down syndrome.
The concept of risks and risks calculation can be very complex and confusing. It is important to consult a doctor who can explain this to you.
This involves insertion of a long, slender needle and extracting some amniotic fluid after 15 weeks of pregnancy. It is a diagnostic test and carries a small risk of miscarriage (about 0.5% or 1-in-200). Amniotic fluid contains shed fetal skin. Fetal cells are harvested and cultured in the laboratory. The chromosomes are analyzed for abnormalities. The process takes between 10 to 14 days. Newer laboratory techniques, such as FISH (fluorescent in-situ hybridization), takes 24 to 48 hours. It utilizes 5 probes and tests for Down syndrome (Trisomy 21), Edward syndrome (Trisomy 18), Patau syndrome (Trisomy 13), X and Y chromosome abnormalities.
Chorionic villous sampling (cvs)
Cvs is essentially a placental biopsy. Pieces of placental tissue (chorionic villous) which contains fetal DNA is obtained for analysis. Depending on the location of the placenta, cvs can be done either through the trans-abdominal or trans-cervical (neck of the womb) route. Cvs is performed after 10 weeks (usually 11-12 weeks) under ultrasound guidance. It carries a higher risk of miscarriage (1% or 1-in-100) but can be done earlier compared with an amniocentesis. Cells from the extracted chorionic villi are cultured and analyzed in the same manner for chromosomal abnormalities.
To test or not to test? - That is the question.
Women today have many choices. The sheer number of antenatal tests that are available for any expectant mother is enough to make her feel uneasy. Although the chances of having a healthy baby is very high even for a woman over the age of 40, an increasing number of women are choosing to undergo antenatal testing.
A couple should be aware of the tests that are currently available, what the tests involve, the benefits and risks, the accuracy and when the results can be available. It is important to know if it is screening test or a diagnostic test and how to interpret the results. Make sure you have all the information before you decide. You need to understand that antenatal tests cannot detect all problems and a negative test cannot guarantee a perfectly healthy baby. Furthermore, no test will be able to determine how severe an abnormality or disability may be.
Questions to ask about the test:
What is the test for? What are the benefits?
What does it involve?
Is it safe? For me? For my baby?
What are the complications?
What happens if the test is positive?
Who would be doing the test? What is his/her experience?
How much would it cost?
How sensitive is the test? How accurate is the test?
What are my options if I do not have the test?
Although most doctors would advise an amniocentesis for women over the age of 35, the risk of chromosomal abnormality should be taken in context. A risk of 1-in-200 may be high but 199 of 200 (or 99.5%) the baby will be normal. Even at the age of 40, the odds of having a healthy baby are in her favour. Furthermore, she may have been trying to conceive for many years. However, antenatal tests should certainly be considered if there is a family history of genetic disease, previous baby with a birth defect or a recent exposure to a serious infection such as rubella or toxoplasmosis.
Antenatal screening tests (such as ultrasound scan) for fetal abnormalities are usually non-invasive and hence do not cause any harm to the baby. In contrast, however, diagnostic tests are usually "invasive" (involves sampling with a needle or small cannula / tubing) there is a procedure-related risk of miscarriage between 0.5 to 1%. However, the sensitivity (detection rate) of screening tests is not high for example the triple test in the second trimester for Down's syndrome.
Although, an invasive test such as amniocentesis can detect Down's syndrome accurately, many women are anxious about the risk of miscarriage. A combination of tests will improve the detection rate of Down syndrome, for example. First trimester maternal serum markers (blood test), coupled with ultrasound scan between 11 to 13+6 weeks (NT & nasal bone) will detect more than 90% of Down syndrome. Many women are therefore opting for this, rather than jeopardize the pregnancy by doing an amniocentesis.
Albeit the choice of antenatal tests is a personal one, couples ought to have all the information available to make an informed decision. It is essential to weigh all the pros and cons, including the religious and cultural implications. Seek out local experts who will be able to help in the decision-making process.
It is no longer uncommon for women today to have their babies after 35. Although the risk of pregnancy and childbirth is increased, the majority of women after 35 have healthy babies. Nonetheless, to ensure an optimum outcome for both mother and her baby, it is essential to be in the best of health before pregnancy, to seek early and frequent antenatal care and have the appropriate antenatal tests to detect any problems which may arise. Steps can then be taken early to reduce the risk to the mother and her baby.
Dr Patrick Chia, September 2006, © FMGC