Not Medical Advice: The mother is most probably in her 16th week of pregnancy.
From eight to about 20 weeks, the baby will be measured from crown to rump as below:
Then from about 20 weeks, your baby will be measured from crown to heel. See chart here.
From early in pregnancy, babies grow at different rates, so these numbers are merely averages. Your baby's actual length and weight may vary substantially. By full-term, your baby may end up weighing less than five pounds or more than nine.
Check out Parents.com's Week-by-Week Pregnancy Tips to ensure you don't miss any important pregnancy tips along the way from week one to delivery.
And, increase your odds of a healthy pregnancy by following these 17 Tips for a Healthy Pregnancy.