Week 10 to 11

The major components of the face arise from two important tissue types – pharyngeal arches and neural crest cells. In the developing embryo, there are six pharyngeal arches.  The pharyngeal arches form from mesoderm about four weeks after conception. Each pharyngeal arch has its own blood vessel, cranial nerve, and bar of cartilage which will later form bones. Neural crest cells are special cells that come from areas next to the neural tube.⁷

Yes! In the 11^th week after conception, the fetus starts urinating into the amniotic cavity. By the last month of pregnancy, the fetus actually excretes half a liter of urine every day.⁹  Around 11 weeks after conception, the fetal intestine begins to absorb water and glucose from amniotic fluid that the fetus swallows, too.¹⁰ Furthermore, the fetus’s respiratory tract also absorbs much of the water that the fetus swallows. Therefore, it is highly important that the amniotic fluid gets recycled quickly. In fact, the water content of amniotic fluid completely changes every three hours!¹¹ 

During the pregnancy, maternal antibodies can transfer to the developing fetus. The earliest evidence of antibodies entering the fetal blood is from a study done 11 weeks after conception.¹² The number of antibodies in the fetus’ bloodstream rises continuously from 15 weeks after conception until birth, with the sharpest increases in the last month of pregnancy.¹³ At birth, the baby usually has a higher concentration of antibodies than the mother to keep the baby from catching dangerous diseases.¹⁴