Summary
Highlights
Pregnancy typically lasts about 40 weeks, starting from the first day of the last menstrual period, divided into three trimesters. The first trimester is about 13 weeks. Although the first two weeks aren't technically pregnancy, the body prepares for it, with ovulation occurring around the second week. Conception happens when a sperm fertilizes an egg, usually in the fallopian tubes, combining genetic material to form a unique genetic code. This new single cell, a zygote or embryo, then develops into a blastocyst by week three, a hollow ball of cells with an inner group forming the baby and an outer group forming nourishing tissues.
During week four, the blastocyst moves into the uterus and implants itself in the uterine lining. Weeks five to ten are the embryonic period, where major organs like the brain, spinal cord, and heart begin to grow and the heart starts to beat. The placenta and umbilical cord also develop, providing nutrients and oxygen to the embryo. Bones and muscles start forming, and by the end of this period, the embryo begins to look more human.
By the end of week 10, the embryo is called a fetus, measuring about 1.25 inches. In the following weeks, arms and legs grow, fingers and toes develop, and the baby's face becomes well-formed. By the end of the first trimester, the baby is almost three inches long. The mother experiences many changes due to fluctuating hormone levels, including missed periods, nausea (morning sickness), tender breasts, mood swings, constipation, weight changes, food cravings, and increased fatigue. It's important to consult a healthcare provider with any questions or concerns.