Conditions Screened
What are Chromosome Differences?
Inside each of the cells in our body, there are string-like structures called chromosomes which package all of our DNA. DNA contains genes that instruct our body how to grow, develop and function on a day to day basis. Some people have extra or missing chromosomes, which means that they have a chromosome difference. When the unborn baby has a chromosome difference there may be long term effects on health and learning. Sometimes having a chromosome difference can have severe effects and results in the loss of the pregnancy.
How Often do Chromosome Differences Happen?
- Two chromosome differences that can happen are trisomy 21 (Down syndrome) or trisomy 18 (Edwards syndrome).
- Any pregnant person has a chance to have a baby with trisomy 21 or trisomy 18. This chance increases with the age of the mother (or the age of egg donor).
- Trisomy 21 and trisomy 18 usually happen by chance in the sperm or the egg that made the pregnancy, and do not generally run in families.
Maternal Age/ Age of Egg Donor * | Chance of Trisomy 21 (at birth) | Chance of Trisomy 18 (at birth) |
---|---|---|
21 | 1/1470 | 1/15291 |
22 | 1/1452 | 1/15038 |
23 | 1/1430 | 1/14684 |
24 | 1/1400 | 1/14245 |
25 | 1/1362 | 1/13699 |
26 | 1/1315 | 1/13055 |
27 | 1/1255 | 1/12270 |
28 | 1/1182 | 1/11351 |
29 | 1/1095 | 1/10341 |
30 | 1/994 |
1/9234 |
31 | 1/881 | 1/8084 |
32 | 1/759 | 1/6935 |
33 | 1/634 | 1/5831 |
34 | 1/513 | 1/4812 |
35 | 1/403 | 1/3905 |
36 | 1/308 | 1/3121 |
37 | 1/231 | 1/2463 |
38 | 1/172 | 1/1923 |
39 | 1/129 | 1/1489 |
40 | 1/98 | 1/1145 |
41 | 1/76 | 1/875 |
42 | 1/61 | 1/667 |
43 | 1/50 | 1/506 |
44 | 1/43 | 1/383 |
45 | 1/38 | 1/289 |
*Ages at expected time of birth.
Adapted from:
JK Morris and NJ Wald. J Med Screen 2007;14:5-7
Which Chromosome Differences does Prenatal Screening Test for?
Currently, multiple marker screening in Ontario (eFTS and MSS) will offer information about:
- trisomy 21 (Down syndrome)
- trisomy 18
NIPT that is funded by the Ministry of Health (MOH) or paid for out of pocket will offer information about:
- trisomy 21 (Down syndrome)
- trisomy 18
- trisomy 13
- sex chromosome differences
Nominate a Condition
Have your voice heard! Did you know you can nominate a condition for addition to the prenatal screening program in Ontario?