5 weeks

Week 5 of Pregnancy
Deep in your uterus your embryo is growing at a furious pace. At this point, he's about the size of a sesame seed, and he looks more like a tiny tadpole than a human. He's now made up of three layers — the ectoderm, the mesoderm, and the endoderm — which will later form all of his organs and tissues.

The neural tube — from which your baby's brain, spinal cord, nerves, and backbone will sprout — is starting to develop in the top layer, called the ectoderm. This layer will also give rise to his skin, hair, nails, mammary and sweat glands, and tooth enamel.

His heart and circulatory system begin to form in the middle layer, or mesoderm. (This week, in fact, his tiny heart begins to divide into chambers and beat and pump blood.) The mesoderm will also form your baby's muscles, cartilage, bone, and subcutaneous (under skin) tissue.

The third layer, or endoderm, will house his lungs, intestines, and rudimentary urinary system, as well as his thyroid, liver, and pancreas. In the meantime, the primitive placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already on the job.
~taken from babycenter.com
http://www.babycenter.com/6_your-pregnancy-5-weeks_1094.bc

We're telling our parents tonight so I am beyond excited. As for symptoms, nausuea, fatigue, sore bbs still around. I'm so nervous about the sonogram on Jan. 8, everything is going great so I shouldn't worry but I can't help it, I'm so scared that something will be wrong. Anyway just counting the days until the u/s. I'll post about the parents reactions soon. :)