Prenatal testing in the first trimester of pregnancy

Routine testing

This is based on blood tests to detect suspected infections with microorganisms that can harm the fetus (rubella, hepatitis B and C, syphilis, HIV, cytomegalovirus, toxoplasma), on blood group and Rhesus factor, and on screening for heterozygosity (carrier status) for beta thalassaemia.
Urine tests are also done for possible infection, diabetes and protein in the urine (proteinuria), as well as tests to rule out cervical cancer.

Scan at weeks 6–8

The first transvaginal scan confirms that the pregnancy is inside the uterus and whether it is a single or multiple pregnancy, and the heartbeat of the embryo is seen for the first time.

Nuchal translu­cency and first-trimester biochem­ical markers (weeks 11–13)

Nuchal translucency is seen on ultrasound and is caused by lymph fluid under the skin at the back of the fetus’s neck. Normally it measures less than 3 millimetres.

Measuring the nuchal translucency in weeks 11–13 of pregnancy, combined with the mother’s age and the levels of beta human chorionic gonadotrophin (β-hCG) and the protein PAPP-A in the mother’s blood plasma, can detect up to 92% of pregnancies with Down syndrome.

With the addition of other ultrasound markers (absent / underdeveloped nasal bone, Doppler of the ductus venosus and the tricuspid valve, assessment of the angle between the upper jaw and the face), it is claimed that up to 97% of pregnancies with Down syndrome can be identified.

Down syndrome or trisomy 21

Down syndrome, the most common genetic syndrome, is characterised by the presence of 3 copies of chromosome 21. Affected newborns have intellectual disability, abnormalities of the heart and of hearing, and other problems.