The following information may help to address your question:
amniocentesis (usually performed at about 15-18 weeks gestation) or chorionic villus sampling (CVS) (at about 10-12 weeks gestation). Genetic testing is performed on the fetal DNA to look for a mutation in the FGFR3 gene known to cause achondropasia. It is generally preferred that the parent with achondroplasia have genetic testing first before prenatal testing is performed.one or both parents have achondroplasia, then testing can be performed during the first or second trimester. In these pregnancies, fetal is obtained by
About 80 percent of people with achondroplasia have average-size parents; these cases result from new mutations in the FGFR3 gene. Routine prenatal ultrasounds may identify short fetal limbs around 27 or 28 weeks gestation and raise the possibility that the fetus could have achondroplasia. A 3D ultrasound may be used to look for other features of achondroplasia. To confirm the diagnosis, fetal DNA can be obtained by amniocentesis and analyzed for FGFR3 .
If you are interested in pursuing prenatal diagnosis for achondroplasia, you should discuss your options with a health care provider or a genetic counselor.