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.
Hereâs what you need to know about how many weeks, months and trimesters there are in a pregnancyâand where you fit in. There are 40 weeks (or 280 days) in a pregnancy, starting from the first day of your last menstrual period. Keep in mind, however, that only about 30 percent of pregnancies last 40 weeks.