First trimester screening combines fetal ultrasound and blood tests for the mother. It’s done during the first trimester of pregnancy, during weeks 1 to 12 or 13. It can help find out the risk of the fetus having certain birth defects. This includes chromosome defects such as Down syndrome (trisomy 21), or trisomy 18 or 13.
First trimester screening may include:
If first trimester screening is abnormal, you may need more testing for diagnosis. This may include chorionic villus sampling, amniocentesis, or another ultrasound.
First trimester screening involves an ultrasound and blood tests. These are low-risk tests. But if the tests are not done at the right time during the pregnancy, the results may be wrong. For example, this might happen if your due date was miscalculated. This can cause unnecessary worry and concern for you and your partner.
First trimester screening is not 100% accurate. It’s only a screening test to see if there is an increased risk for a birth defect. It also helps to see if you need more testing or monitoring during your pregnancy.
False-positive results can show a problem when the fetus is actually healthy. False-negative results show a normal result when the fetus actually does have a health problem.
First trimester screening generally involves the following tests. They are done between weeks 10 and 14: