X-linked recessive diseases are severe hereditary diseases that are manifested solely in males. If the mother is a carrier of an X-linked recessive disease, she can either have a healthy girl, a healthy girl who is a carrier like the mother, a healthy boy, or a boy that becomes ill with the X-linked disease. Current practice in Norway is that all pregnant women at increased risk of having a child with an X-linked recessive disease, are eligible for an invasive test (chorionic villus sampling or amniocentesis), without any determination of the fetal sex beforehand. Annually, 40-60 invasive tests are performed in this group of pregnant women in Norway.

In non-invasive prenatal testing (NIPT), a blood sample of the pregnant woman is used to identify fetal sex. The method is based on the analysis of cell-free fetal DNA found in maternal blood early in pregnancy. The purpose of using NIPT for fetal sex determination is to avoid unnecessary invasive testing of pregnant women who carry a female fetus.

We have summarized research findings on NIPT's diagnostic accuracy for fetal sex determination, as well as discussed clinical, health economic and ethical consequences related to NIPT used for fetal sex determination. Based on the findings:

• Diagnostic accuracy of NIPT for fetal sex determination is very high.
• Maternal blood samples taken in gestational week 7 or later provide more reliable results than blood samples taken before week 7.
• Assuming 50 pregnant women are tested every year, 21 of these will avoid invasive testing.
• Introduction of a program where NIPT is used in determination of fetal sex, will increase the annual total health care cost expendings by 197,000 Norwegian kroner.