Over the next few days, the heart starts to develop. It starts beating at the 18th day! By the end of the 3rd week of gestation (5 weeks after your period), the embryo will be around 2 mm long. All the baby’s major organs are in development: eyes and ears start to take shape. The neural tube that will become the brain and spine appears and the kidneys start to take shape. The embryo doubles in volume every day.

This week

Baby measures about 0.2 mm (from head to heel)
Baby weighs about – no available data