Conception to about the 12th week of pregnancy marks the 1st trimester. A missed period may be the first sign you are pregnant. Other changes will also occur like: nausea, sore breast, mood swings, cravings, ect.
At for weeks your baby is developing. The nervous system, heart, and arm and leg buds have started to form. Your baby is now an embryo. By 8 weeks all major organs have begun to form. Your baby now is considered a fetus. By 12 weeks the nerves and muscleses start to work together
Your second trimester might be easier than your first. Your nausea might lessen or even go away. Your "baby bump will start to show. By the end of this trimester you may even begin to feel your baby move.
At 16 weeks the baby's musculoskeletal system continues to form. Skin begins to form. Your baby begins sucking motion with the mouth. It is about 4 to 5 inches long. At 20 weeks your baby is more active. Nails on both hands and feet have formed. Your now about half way through your pregnancy.
As the baby grows and puts more pressure on your internal organs, you may find it hard to breathe and have to urinate more frequently. You will start to swell if haven't already. You will have tender breast which may leak watery pre-milk. The baby will move lower in your abdomen, Contractions will start which can be a sign of real or false labor.
Your baby's bones are soft but fully formed. Its eyes cam open and close. Lungs are not fully formed but practice breathing movements occur. Your baby's body begins to store vital minerals. Your baby is gaining about 1/2 pounds a week. By 37 weeks your baby is considered full term and its organs are capable of working on their own.