The pancreas begins to produce insulin, a hormone that regulates blood sugar levels. This article's factual accuracy is disputed. The intestines, which had been developing inside the umbilical cord, have now begun slipping into the embryo's abdominal cavity. Prev Article Next Article Having a baby is one of the most miraculous things we can do as human beings, but we are also naturally curious creatures. In girls, development of external sex organs remains pretty much static over time. At around week 7 , the Y chromosome signals for the start of testosterone production, and male genitalia begin to develop. He's over one and one-quarter inches long now, or about the length of your index finger from its tip to the first joint. Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either male or female organs. For example, some studies claim girls are, on average, more verbally fluent than boys, but boys are, on average, better at spatial calculation. Several important digestive functions begin around this week. Not sure if an animal has been given hormones? A 5-alpha-reductase deficiency results in atypical development characterized by female phenotype or undervirilized male phenotype with development of the epididymis , vas deferens , seminal vesicle , and ejaculatory duct , but also a pseudovagina. However, despite the wide range of these beliefs, the fact of the matter is that reliably determining the sex of a fetus goes far beyond superstition. Testosterone will also control the descending of the testes from the abdomen into the scrotum.