KUB, or the combined ultrasound and biochemical test, is a voluntary examination offered between weeks 11 and 14 of pregnancy. Its purpose is to calculate the probability that the fetus has certain chromosomal conditions, mainly trisomy 21 (Down syndrome), trisomy 18 and trisomy 13. It does not provide a diagnosis; it gives a probability estimate.

KUB consists of two parts. The first is a blood test taken from the pregnant person. The sample is analysed for specific substances, such as PAPP-A and free Beta-hCG. The levels of these substances change naturally during pregnancy, and they form part of the probability assessment.

The second part is the ultrasound measurement. During the scan, the nuchal translucency is measured — a naturally occurring fluid-filled space at the back of the fetal neck. The thickness is measured and compared with the gestational age. This measurement is done with precision and is included in the probability calculation.

In addition, gestational age can be confirmed and the number of fetuses determined. Detailed organ development, placenta location or amniotic fluid volume are not assessed at this stage — these are examined later at the routine ultrasound in week 18–20.

The result is expressed as a probability. If the probability exceeds a certain threshold, additional examinations may be offered, such as NIPT or amniocentesis.

Alma’s tips 🌿

• KUB combines a blood test and an ultrasound measurement of nuchal translucency.

• It provides a probability — not a diagnosis.

• It does not assess anatomy, organ development or amniotic fluid.

• Further testing may be offered if the probability is elevated.