what is the developing fetus nourished by
What a difference a week makes! This week, a sonographer can see your baby via ultrasound as a tiny white image tucked within the gestational sac. And his heart is beating! For these first few weeks in your baby-to-be's development, he'll be nourished by the yolk sac. The yolk sac provides all the nutrients the embryo needs and produces blood cells until the placenta fully forms later in the pregnancy.