Over the past decade, the number of women having kids after age 35 is on the rise due to prioritizing education and career. Women who get pregnant in their late 30s or 40s have a higher risk of having a baby with genetic disorders, and the risk does go up proportionally with age. However, it does not mean they definitely shouldn’t get pregnant after age 35. Despite the risks, women older than 35 years can have healthy babies. Thanks to new technologies, providing accurate and safe DNA testing before birth in the first trimester of pregnancy.
What do you need to know?
I hear quite often from women in 30s that they are worried about their aging and having a baby with genetic disorders, but they do not know mostly what are the risks and how aging affects the risk of having a baby with a genetic defect? Moreover, what are the update DNA tests to check if the fetus has genetic disorders? Here I provide you all the answers.
What are the genetic risks of later childbirth?
First let me tell you about different types of genetic disorders, which are classified into three categories (Nussbaum et al. 2007): Chromosomal Abnormalities ( Down Syndrome is the most common chromosomal defect), Single-Gene Disorders, Complex Genetic Disorders (like cancer, Alzheimer’s disease, heart disease,…)
Increased maternal age increases the risk of having a baby with only chromosomal abnormalities (such as Down syndrome). Studies have not shown any increased risk for having a baby with single-gene disorders and complex genetic disorders with increasing age of the mother.
Genetic Disorder Categories
Chromosomal abnormalities: they are abnormalities in number (extra or missing chromosomes) or structure of chromosomes. For example, Down syndrome (or trisomy 21) is because of an additional copy of chromosome 21 and is the most common form of chromosomal disorder in humans. Trisomy 21 is diagnosed with an intellectual disability and other defects such as congenital heart disease. Other trisomies observed in humans are trisomy chromosome 13 and trisomy trisomy 18 (Edwards syndrome).
Single-gene disorders: they are because of mutations in only one gene. They are usually diagnosed early in life. The best examples are sickle cell anemia, Thalassemia, Hemophilia. They exhibit apparent clinical symptoms, and they have known inheritance pattern. Most such disorders are rare.
Complex genetic diseases: the complex disorders (also known as multifactorial or polygenic) are caused by the simultaneous effect of multiple genes, environmental and lifestyle factors such as diet, and they develop typically later in life. The examples of complex genetic diseases are type 2 diabetes, obesity, Alzheimer’s disease, heart disease, autism, Parkinson’s disease, multiple sclerosis, cancers, schizophrenia, and depression.
How does aging affect the risk of having a baby with a chromosomal abnormality?
The general risk of having a baby with a Chromosome Abnormality is not high. However, as a woman ages, the risk of having a baby with chromosomal defect increases (American College of Obstetricians and Gynecologists, accessed in January 2019). The risk of having a baby with Down syndrome is as following:
|At age 20||1 in 1,441|
|At age 25||1 in 1,383|
|At age 30||1 in 959|
|At age 35||1 in 338|
|At age 40||1 in 84|
|At age 45||1 in 35|
|At age 46 and over||1 in 25|
The definition of advanced maternal age varies to a certain degree among genetic centers but is usually at least 35 years, and women after age 35 are considered as high risk for having a baby with a chromosome abnormality.
Is there DNA testing to find out the risk of having a baby with a chromosome defect?
Yes, there are screening tests that they can detect if a fetus has a chromosome disorder. Here, I am going to introduce you a unique non-invasive prenatal screening test (NIPT), using fetal DNA circulating in mother’s blood, which first became available in the USA in 2011 and is now offered throughout the world (Rafi et al. 2016).
Today the recent non-invasive test (NIPT) is revolutionizing genetic testing of the fetus. I call it a golden method. A mother’s blood contains DNA of her child, even in the early phases of pregnancy. This so-called “cell-free fetal DNA” (cffDNA) can now be tested for the presence of chromosomal disorders in the unborn child by taking a simple blood sample from the mother. This test does not have any risk, and blood sampling can be done in a private’s office. This method is widely validated and is a highly accurate test with high sensitivity (99%) and specificity (99.5%), which can be used from 10 weeks in pregnancy to determine the risk of trisomies.
Until quite recently, prenatal testing was done by amniocentesis and chorionic villus sampling (CVS). Both of these tests are invasive and have a risk of miscarriage. During amniocentesis, a needle is used to collect amniotic fluid surrounding fetus (containing fetal cells), and CVS samples placenta (Snyder et al. 2016).
- Nussbaum RL, McInnes RR, Willard HF, Hamosh A. Thompson & Thompson Genetics In Medicine. Philadelphia: Elsevier; 2007.
- American College of Obstetricians and Gynecologists. Having a Baby After Age 35: How Aging Affects Fertility and Pregnancy. https://www.acog.org/Patients/FAQs/Having-a-Baby-After-Age-35-How-Aging-Affects-Fertility-and-Pregnancy.
- Rafi I, Hill M, Hayward J, Chitty LS. Non-invasive prenatal testing: use of cell-free fetal DNA in Down syndrome screening. Br J Gen Pract 2017; 67 (660): 298-299.
- Snyder M. Genomics & personalized medicine. New York: Oxford University Press; 2016.