Birth height and birth weight has little input on actual adult height. Birth measurements are based on intra-uterine nutrition and placental functioning.
As others have noted, you can get a better idea as a child grows, and settles into their "curve" on the growth charts. Even those aren't always accurate in predicting adult height though--a early or late bloomer will throw the prediction off.
--Mimi
Mom to Lala (2004), Bonus Mom to Big Sis 1 (1991) and Big Sis 2 (1992)
Grammy to Big Kindy Kid (2011), Big Pre-K Kid (2012),
Grandbaby Appendage (2014), and New Baby Grandboy (summer 2017)