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.
Airline travel. When you're pregnant, the safest time to travel is during your second trimester (18 to 24 weeks), when your risks for miscarriage and preterm labor are lowest. During your third trimester, it's best to stay within 300 miles of home, in case of sudden changes that need medical attention. Airplane travel tips include the following: Check with the airline for its requirements before you book a flight. Some airlines do not allow women more than 35 weeks pregnant to fly. Carry written documentation of your due date when traveling. Some airlines ask to see this information. Wear your seat belt strap over your lower lap/upper thighs.