Describe the major developments during each trimester of human gestation.

The first trimester

Most women ovulate once a month, about two weeks after their last menstrual cycle. Ovulation is the release of an egg. If you have sexual relations before, during, or within 24 hours of ovulation, sperm can travel from the vagina into your fallopian tubes and fertilize the egg. Sperm can live in the body for up to five days, so your chances of conceiving are higher if you have intercourse in the days leading up to ovulation.
These developments continue up to week 10, which is the end of the embryonic stage. Your baby’s sex organs will have formed by the end of this stage, although it's too early to determine the baby’s sex on an ultrasound.