I am 13 weeks pregnant and went for an nuchal translucency, which came out at 2.2mm in thickness which the doctor said is thicker than normal?

Not that simple: Nt scan is one of many screening tests used to assess for risk of a major chromosomal abnormality. There is a range of "normal" that has been established by scanning thousands of pregnancies. As with any screening test, a cutoff is chosen somewhat arbitrarily based on statistics. Most studies use a cutoff of 2.5 or 3.0 for "abnormal." NT is combined with blood tests to determine overall risk.