When a person with a penis has an orgasm (and ejaculates), millions of sperm are released within the fluid that’s often called “cum.” The more formal name is “semen.”
Once a month, people with uteruses release an egg from one of their ovaries. The fallopian tube takes the egg from the ovary toward the uterus (or womb).
During penis-vagina sex, the penis ejaculates in the vagina. That ejaculation shoots millions of sperm up into the vagina, where they race through the cervix (the opening to the uterus), then the uterus and into the fallopian tubes hoping to find an egg. If they find one, fertilization may occur.
Each month, hormones are released that cause changes to the uterus. At one point in the cycle, the body creates a potential home for the fertilized egg in the wall of the uterus. Someone can only become pregnant during the days when the uterus is ready. If the fertilized egg doesn’t attach during this part of the menstrual cycle, the uterine lining is expelled from the body.
Pregnancy starts when the fertilized egg attaches to the uterus. Once it’s attached, the egg grows into an embryo and eventually a fetus.
The body goes through many changes during pregnancy. Weight gain occurs to help the fetus grow and be protected. The pregnant person produces more blood, so that there’s enough for two bodies instead of one. Toward the end of pregnancy, it’s common for breasts to enlarge and get ready to produce milk. And in preparation for the final delivery of the baby, some muscles and ligaments (ligaments attach muscles to bones) relax, so that the baby has room to get out. The entire process, from ejaculation to delivery, takes about 40 weeks.
