The Genoo test and NIPT come up often as tests that give news about the baby in early pregnancy from a blood draw alone. The names are similar, but the two tests check different things and can be taken at different times. The Genoo test identifies the baby's sex, while NIPT screens for the risk of chromosomal abnormalities, so one cannot replace the other.
Once you are clear about what you want to know, it becomes much clearer which test to have and when. This article sets out when you can start each test, what each one checks, and what is useful to know before having them.
When can you start the Genoo test and NIPT?
Fragments of the baby's DNA released from the placenta circulate in the mother's blood, and their proportion rises as the pregnancy progresses. The point at which this proportion is high enough sets the earliest week for each test, so even though the blood is drawn in the same way, the starting times differ.
If you want to know the sex early, the schedule is built around the Genoo test; if you also want to look at the risk of chromosomal abnormalities, it is built around NIPT, which is carried out once the proportion of fetal DNA has stabilised. Keeping the timings below in mind helps when planning clinic visits.
- Genoo test — a blood draw is possible from around week 6 of pregnancy, and the sex is identified by whether a Y chromosome is present
- NIPT — carried out from week 10 of pregnancy onwards, once the proportion of fetal DNA has stabilised
- Sex on ultrasound — checked visually at around week 16 of pregnancy, when the shape of the genitals becomes clear
Do the Genoo test and NIPT check different things?
Because the names are similar and the blood draw is the same, it is easy to assume the two tests serve the same purpose, but the questions they answer are entirely different. The Genoo test looks at a single sex chromosome and reads the result as boy or girl, whereas NIPT is a screening test that looks broadly at whether there are numerical abnormalities in several chromosomes and at the level of risk.
Both tests work on the same principle of analysing fragments of fetal DNA in the mother's blood, but what they read from it differs. Having one does not make the other unnecessary, and it is more accurate to understand sex identification and chromosomal screening as tests carried out for separate purposes.
- Genoo test result — read as a boy if a Y chromosome is detected, and as a girl if it is not
- What NIPT checks — the risk of major chromosomal abnormalities, including Down syndrome
- Detection rate — the detection rate of NIPT for Down syndrome is reported at around 99%
What is useful to know before having the Genoo test or NIPT?
NIPT is a screening test designed to identify the possibility of chromosomal abnormalities in advance, so a high-risk result does not confirm a diagnosis on the spot. A final conclusion is reached only after a separate confirmation step, such as amniocentesis.
As a blood test, it can also be affected by variables. If the proportion of fetal DNA is not sufficient, the result cannot be read and the blood has to be drawn again. With twins, the genetic material is mixed, which makes interpretation more difficult, so it is safer to discuss this with the medical team before the test.
- Complementary tests — choose the Genoo test if you want to know the sex, and NIPT if you want to know the risk of chromosomal abnormalities
- Possible retest — if the proportion of fetal DNA is low, no result may be produced and the blood may need to be drawn again
- With twins — interpreting the genetic material is more difficult, so this should be discussed with the medical team before the test
