The Baby's Exact Size
Six weeks after your last menstrual period, your baby is four weeks post-conception. In the sixth week, he is only about one quarter-inch long. But, by the end of the week, he will have nearly doubled in size. Because of the rapid development occurring this week, your baby is growing so fast that you can see a measurable difference after just a couple of days.
A Six-Week-Old Embryo is the Size of...
It may be hard to visualize the six-week-old embryo's size based on numbers alone, so comparison might help. A quarter-inch is about the same size as a lentil, pea or a grain of rice. The embryo is roughly half the size of your own pinky-nail at this stage in its development. Although small, it is far from microscopic.
What the Baby Looks Like
Despite its small size, a baby is beginning to look like a living being. She has a large head about the same size as her body, where dark spots mark the beginnings of eyes and nostrils. Tiny buds mark the beginnings of arms and legs, and her heart is beating at an impressive 140 beats per minute. Inside the newly-formed embryo are the beginnings of intestines, lungs, muscles, bones and even a small brain.