Normal acetylcholine and receptors. Nicotine affects the neurotransmitter acetylcholine and its receptor. This receptor is located in many brain structures and body organs. It carries messages related to respiration, heart rate, memory, alertness, and muscle movement.
Around the middle of the second trimester, movement of the fetus may be felt. At 28 weeks, more than 90% of babies can survive outside of the uterus if provided high-quality medical care. The third trimester is from 29 weeks through 40 weeks.
The First Trimester (Weeks 1-13) The first trimester is typically the shortest for you, because the first 3-4 weeks or more of your pregnancy, you do not even know you are pregnant. In fact, weeks 1-2 are the week of your last normal menstrual period, and when you ovulate. Most mothers won't be able to take a pregnancy test until around week four, and some are even later than that. This first trimester sees an incredible shift in your baby.