NIPT Sex chromosome aneuploidy or fetal sex inconclusive

This information is not intended to diagnose health problems or to take the place of medical advice

or care you receive from your physician or other health care professional.

You recently had a blood test to screen for chromosome disorders in the fetus and were told:

NIPT is unable to provide a clear answer about

fetal sex or sex chromosome changes (or both)

Did you know?

• There are two different sex chromosomes:

the X chromosome and the Y chromosome.

• Most males have one X and one

Y chromosome (XY). Babies with a Y

chromosome develop as a male.

• Most females have two X chromosomes (XX).

• A difference in the number of X and Y

hromosomes is called sex chromosome

aneuploidy or “SCA”.

• Most of the DNA in the NIPT sample comes

from the woman being tested. Only a small

amount of DNA is from the pregnancy.

The main purpose of NIPT is to screen for major chromosome

conditions (Down syndrome, trisomy 18, and trisomy 13). Your

test result shows that your pregnancy is at low risk for these

three conditions.

NIPT also includes a study of the sex chromosomes, but

result is not always possible. Babies can be born with a change

in the total number of sex chromosomes, such as only one X

(X), an extra X (XXX or XXY), or an extra Y (XYY). NIPT

checks for the presence or absence of the Y chromosome in

the fetus and

estimates how many are present. The test also

measures

how many X chromosomes are present. Most often

an extra X or Y does not have a big impact on a baby’s

development.

Why was the fetal sex not reported?

The Y chromosome is much smaller than any of the other

chromosomes being studied. The smaller size means there is less “Y” DNA to examine at the lab. This makes it

harder to confirm the presence or absence of the Y chromosome in some cases. The lab is careful to report fetal

sex only if the result is very clear. The lab reports the result as “inconclusive” when there is not enough information

from

the sample to provide a reliable result.

Why was a “sex chromosome aneuploidy” (SCA) result not reported?

Trying to estimate

the

number of sex chromosomes

from a fetus can be complicated. The Y chromosome is small and can be hard to

measure

, but the X chromosome can sometimes be even harder to measure. Not only does the fetus have one or

two X chromosomes, but there are also X chromosomes from the mother.

To complicate things even more, the

mother or the placenta may have some cells with an atypical number of X‘s (either more or less than the usual

number). This is fairly common and not usually related to a medical condition or health problem. However, it c

make it hard to

measure how many X chromosomes a fetus has. When the sample does not have clear

information to give a reliable result for SCA, the lab reports the result as “inconclusive”. There may still be enough

information to predict the fetal sex f

or some pregnancies. Twin pregnancies do not include testing for SCA

conditions.

Does this mean a problem in the baby

Usually n

ot. While there is still a small possibility for a chromosome condition in the baby, most women who get

this r

esult have healthy pregnancies.

Can I take the test again? When the fetal sex or the sex chromosome number cannot be reported,

re-testing is not offered. Repeat testing is unlikely to give a reliable result about the sex chromosomes in this

situation.

Should other tests be done if fetal sex or sex chromosomes cannot be reported?

You could consider having a procedure like

chorionic villus sampling (CVS) or amniocentesis to examine the fetal

chromosomes. It may also be possible to request a chromosome study after delivery. The decision to have

additional testing w

ill depend on the details of your pregnancy and the questions you want answered. You may

want to discuss this with your genetic counselor. All pregnancies have a routine ultrasound typically scheduled

between 18 to 22 weeks. Ultrasound is often able to pre

dict the fetal sex and checks for physical birth defects.

However, ultrasound cannot identify most babies with SCA conditions.

More about SCA conditions…

About 1 in every 500 newborns has a sex chromosome aneuploidy (SCA) condition. These conditions happen

randomly and do not run in the family. The three most common SCA conditions are:

Turner syndrome (45,X or Monosomy X)

Turner syndrome is a genetic condition that only happens in females. It is caused by a

missing X chromosome in some or all of a person’s cells. The most common features

in Turner syndrome are shorter height, late puberty and infertility. Girls with this

condition have normal intelligence, but learning delays are possible. Turner syndrome

in a fetus may lead to an early miscarriage. Birth defects, such as heart defects and

malformed kidneys, also happen more often in babies with Turner syndrome.

Klinefelter syndrome (XXY)

Klinefelter syndrome is a genetic condition that only happens in males. It is caused by

an extra X chromosome. Boys with this condition are often tall for their age compared

to boys with typical chromosomes. Motor skills, like sitting and walking, may happen

slightly later than usual. Learning disabilities, like speech delays, are also more

common. The extra copy of the X chromosome also causes low testosterone (the

male sex hormone). This can lead to delays in puberty. In addition, most males with

this condition are infertile due to poor sperm production.

Trisomy X or Triple X syndrome (XXX)

Trisomy X (or triple X syndrome) is a genetic condition that only happens in females. It

is caused by having an extra X chromosome. Girls with this condition are more likely

to have learning and behavior issues than girls with typical chromosomes. These girls

also tend to be tall for their age. This condition does not usually affect puberty or

fertility. Most individuals with trisomy X never know they have this condition unless

special testing is done.

This information is not intended to diagnose health problems or to take the place of medical advice

or care you receive from your physician or other health care professional.