Sex misidentification Mistakes are rare, but they do happen. If your doctor is looking at the ultrasound scan during that point of time, they may notice a penis that is very clearly defined. For example, when a specific genetic disease runs in the family and is gender specific. There is no regulation of ultrasound facilities outside of a medical setting, so their quality can vary wildly, Carr said. Genetic testing Genetic testing methods such as amniocentesis or chorionic villus sampling CVS are also among the early baby gender prediction methods. See a slide show explaining fetal ultrasound at the Mayo Clinic. And the technicians may have limited medical training to interpret the scans, he noted. CVS involves taking a sample of tissue from the placenta specifically, taking a sample from the villi, hairy-like projections of placental tissue and testing that tissue for chromosomal abnormalities. In addition, ultrasound can identify certain birth defects, such as Down syndrome and spinal abnormalities, and investigate pregnancy complications, including miscarriage, according to the March of Dimes. However, these cases are rare. Is it harder to find out the genders if you have twins? If the color turns green, the baby is said to be a girl; if it's blue, a boy may be on the way. If it swings in a circle, the child is thought to be a girl. Lately, as more couples turn to in-vitro fertilization procedures to conceive a child, the issue of selecting the sex of a baby for purposes of "family balancing" rather than for medical reasons is controversial and raises ethical concerns.