By week 15, the fetus is around five inches lengthy and weighs about two ounces. At week 20 -- halfway through the pregnancy -- the fetus is about six inches lengthy and weighs about 10 ounces. Regardless that her fetus is just some inches lengthy, her belly is rising. During this trimester, the mother's breasts will start to produce a yellowish, nutrient-wealthy substance called colostrum, which is able to feed her baby during its first few days of life. Its lungs produce a substance known as surfactant, which can enable the air sacs to inflate for respiratory as soon as it's born. The kidneys, liver, mind, and lungs are all starting to function. If the fetus is a girl, her ovaries are beginning to supply the tens of millions of eggs that she's going to possess for her entire lifetime. Between weeks 16 and 20, the fetus begins to hear and should even be in a position to hear the sound of its mom's voice. The doctor will probably also measure the fundus -- the gap between the top of the mother's pubic bone and the top of her uterus.
