Figures on this vary somewhat, for several reasons: there is no
absolute consensus on precisely what is to be considered a birth
defect; some kinds of birth defects are not discovered until long
after the birth (sometimes months or years later); there is no central
record-keeping agency for all children's health data (a fact which has
both positive and negative implications). Below I've gathered some
material that I believe will meet your needs. I've addressed your
three questions in the order asked.
What are the chances--or odds--a 44 year old pregnant woman will give
birth to a child with a birth defect?
A 40-year-old mother has approximately a 6% to 8% risk of giving birth
to a child with a birth defect. Since the likelihood of most types of
birth defects increases with maternal age, a 44-year-old woman could
be assumed to have a risk over 8%. A 44-year-old mother's risk of
bearing a child with some form of chromosomal abnormality is 1 in 24
(or about 4%). At age 45, the risk of having a child with Down
Syndrome is around 1 in 40 (and some statistics are as low as 1 in
Here are some figures from online sources:
"What is the risk of birth defects in babies of women over 35?
The risk of bearing a child with certain chromosomal disorders
increases as a woman ages. The most common of these disorders is Down
syndrome, a combination of mental retardation and physical
abnormalities caused by the presence of an extra chromosome 21 (humans
have 23 pairs of chromosomes). At age 25, a woman has about a
1-in-1,250 chance of having a baby with Down syndrome; at age 30, a
1-in-1,000 chance; at age 35, a 1-in-400 chance; at age 40, a 1-in-100
chance; and at 45, a 1-in-30 chance."
March of Dimes
"While the general population of childbearing women has a 3% chance of
delivering a child with a birth defect, after age 40 this risk rises
to between 6% and 8%. The likelihood of having a baby with Down's
syndrome is approximately 1 in 365 at the age of 35. This number
increases to 1 in 100 by the age of 40 and up to 1 in 40 at the age of
Somerset Medical Center
Here is a table which shows, year by year, the chance of having a
child with Down's Syndrome, and the chance of having a child with any
Mother's Chance of Chance of Chromosomal
Age at Delivery Down Syndrome Abnormality
20 1 in 1923 1 in 526
21 1 in 1695 1 in 526
22 1 in 1538 1 in 500
23 1 in 1408 1 in 500
24 1 in 1299 1 in 476
25 1 in 1205 1 in 476
26 1 in 1124 1 in 476
27 1 in 1053 1 in 455
28 1 in 990 1 in 435
29 1 in 935 1 in 417
30 1 in 885 1 in 384
31 1 in 826 1 in 384
32 1 in 725 1 in 322
33 1 in 592 1 in 285
34 1 in 465 1 in 243
35 1 in 365 1 in 178
36 1 in 287 1 in 149
37 1 in 225 1 in 123
38 1 in 177 1 in 105
39 1 in 139 1 in 80
40 1 in 109 1 in 63
41 1 in 85 1 in 48
42 1 in 67 1 in 39
43 1 in 53 1 in 31
44 1 in 41 1 in 24
45 1 in 32 1 in 18
46 1 in 25 1 in 15
47 1 in 20 1 in 11
48 1 in 16 1 in 8
49 1 in 12 1 in 7
Dr. Wendy Cox
At what age does this curve of defects in children born to middle-aged
mothers begin to sharply increase?
Rather alarmingly, there is a noticeable increase in non-chromosomal
fetal malformations starting around age 25. At 35, there are markedly
increased risks, since chromosomal abnormalities (including Down
Syndrome) spike dramatically around this time in middle age. Another
big jump in instances of birth defects comes with mothers who are 40
"Researchers conducted this study to examine the effect of maternal
age on incidence of non-chromosomal fetal malformations. Malformations
detected at birth or in the newborn nursery were catalogued
prospectively for 102,728 pregnancies, including abortions,
stillbirths, and live births. Clearly chromosomal defects increase
with age and this was confirmed in the present study by karyotyping.
After excluding infants with chromosomal abnormalities, the incidence
of structurally malformed infants also increased significantly in
women > 25 years of age. The additional age-related risk of
non-chromosomal malformations was approximately 1% in women 35 years
of age or older. The odds ration for cardiac defects was 3.95 (about
times greater) in infants of women >40 years as compared to women
20-24 years of age. The risks of clubfoot and diaphragmatic hernia
also increased as maternal age increased. It was concluded that
advanced maternal age >25 years was associated with a significantly
increased risk of fetuses having congenital malformations not caused
Center for Applied Reproductive Science Archives
"The risk of giving birth to a child with a birth defect does increase
as the mother's age increases. This is probably due to abnormal
division of the egg, called nondisjunction. The traditional age at
which a woman is considered to be at high risk for chromosomal
abnormalities is 35."
Cached copy from WebMD Health
"There are several fetal risks associated with advanced maternal age.
In a study of 379 mature prospective mothers, aged 35 years and older,
in comparison to a control group of 379 prospective mothers, ages 20
to 30, there were five stillbirths in the mature age group and none in
the younger age group (Barton, Bergauer, Jacques, Coleman, Stanziano,
& Sibai, 1997). Furthermore, there is a significant difference in
unexplained fetal death in pregnant women over the age of 35.
According to Fretts & Usher (1997), one in 440 fetal deaths were
unexplained in women 35 and older, whereas, one in 1000 fetal deaths
were unexplained in women younger than 35.
Chromosomal abnormalities in the fetus also increase with maternal
age. In a recent study, in the age group 35 and younger, 63.6 percent
(7 of 11) had normal fetal chromosome makeup; in the elder maternal
age group, 35 and older, only 22 percent (9 of 41) had a normal fetal
genetic makeup (Schmidt-Sarosi, 1998). The most prevalent chromosomal
anomalies are trisomy 21 (Down?s Syndrome), trisomy 18 (Edward?s
Syndrome), and trisomy 13 (Patau?s syndrome). Each of these symptoms
occurs due to an extra chromosome in the cell during embryonic
development. Down?s syndrome is the most frequent in occurrence. The
rate of having a child with Down?s syndrome in a mother at age 25 is
1:2000, a figure that rises to1:200 at age 35, and climbs to 1:40 for
mothers over the age of 40."
Department of Labor Studies and Industrial Relations, Penn State University
"We know that the rate of genetic abnormalities increases with a
woman's age, rising significantly after she has reached the age of 40.
There is not a similar rise in men."
In the last 10-20 years what are, in order the 3-5 most common birth
defects in children born to women over 40?
I have not been able to find that precise figure. I did locate some
detailed statistics from the records of the state of Texas, 1996-1997.
I believe these are likely to be representative of the United States
as a whole.
"The highest rates were found among older mothers for the following
birth defects: hydrocephaly; tetralogy of Fallot; ventricular septal
defect; atrial septal defect; endocardial cushion defect; pulmonary
valve atresia or stenosis; patent ductus arteriosus; Down syndrome;
and Edwards syndrome."
Texas Department of Health
(By "older mothers," the study refers to mothers over 35.)
Google search strategy:
Google Web Search: "birth defects" + "by age of mother"
Google Web Search: "birth defects" + "increase" + "age"
Google Web Search: "maternal age risks"
Thank you for a question that was quite interesting to research. I
hope this information will be useful. If anything is unclear, or if a
link does not function, please request clarification; I'll be glad to
offer further assistance before you rate my answer.