NIPT (non-invasive prenatal testing) is very accurate for determining fetal gender—about 99% or higher—once enough fetal DNA is present in the mother’s blood, usually from around 10 weeks of pregnancy onward, making it most reliable after the first trimester begins. Its accuracy depends on factors like gestational age (too early testing may have low fetal DNA), maternal weight, twin or vanishing twin pregnancies, and rare lab or sample errors, which can sometimes affect results. Although rare, NIPT results can be wrong due to these factors, so results are often confirmed with an ultrasound scan (around 18–22 weeks) or diagnostic tests like CVS or amniocentesis if needed.