First trimester growth delay in trisomy 18.

Neonates with trisomy 18 are usually growth retarded at birth, and delayed growth has been ultrasonigraphically detected antenatally during the second and third trimesters in fetuses with this aneuploidy. We examined the growth patterns of five fetuses with trisomy 18 during the first trimester and compared them with a group of 16 normal control subjects. The crown-rump length of all trisomy 18 fetuses was at least 5 days smaller than expected (mean, 8.2 days; range 5 to 11 days), whereas only two controls had a similar delay (p less than 0.005). We conclude that in patients in whom gestational age is certain by other parameters, significant growth delay detected during the first trimester may be a useful marker for trisomy 18.