Blood test on mother detects fetus's sex at five weeks

A NON-INVASIVE method of detecting a fetus's sex as early as five weeks into pregnancy has been developed.

Knowing the sex of a fetus is important when the mother is a carrier of an X-chromosome gene that can cause a disease such as muscular dystrophy. In this case, a female fetus will be free of the gene or be a carrier, but a male has a 50 per cent risk of inheriting the disease. In these cases, parents may choose to abort the pregnancy or undergo further, invasive testing, which carries a small risk of miscarriage.

Currently in the UK, for example, women can choose invasive testing at 11 weeks, or wait longer for ultrasound identification of sex. Attempts to analyse fetal DNA in the mother's blood for markers of the male-only Y chromosome can give inaccurate results if not enough DNA is available.

To tackle this problem, Hyun Mee Ryu and colleagues at Cheil General Hospital and Women's Healthcare Center in Seoul, South Korea, measured changes on the PDE9A gene that occur in the blood of a pregnant woman. They then worked out the amount of PDE9A changes that were needed to ensure enough fetal DNA was present to accurately identify whether a Y chromosome was present.

In 203 women, the combination of tests faultlessly detected gender as early as five weeks into pregnancy (The FASEB Journal, DOI: 10.1096/fj.11-191429).

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