Technically you can't get pregnant if you have anal sex. To become pregnant, a man's sperm needs to meet a woman's egg. The venue that this usually occurs in is the vagina - not the rectum. However, if the man does not wear a condom, or it slips off or it is worn incorrectly, there is a chance that some sperm may get into the vagina and a pregnancy could occur.
Each month a woman ovulates, on egg is released and travels into the fallopian tube where it remains until a single sperm penetrates it during fertilization which is the union of egg and sperm. The egg can be fertilized for about 24 hours after ovulation. On average, ovulation and fertilization occurs about two weeks after your last menstrual period.
Within 24-hours after fertilization, the egg begins dividing rapidly into many cells. It remains in the fallopian tube for about three days. The fertilized egg, called a zygote, continues to divide as it passes slowly through the fallopian tube to the uterus where its next job is to attach to the endometrium.
First the zygote becomes a solid ball of cells, and then it becomes a hollow ball of cells called a blastocyst. Before implantation, the blastocyst breaks out of its protective covering. When the blastocyst establishes contact with the endometrium, an exchange of hormones helps the blastocyst attach. Some women notice spotting or slight bleeding for one or two days around the time of implantation. The endometrium becomes thicker and the cervix is sealed by a plug of mucus.
Within three weeks, the blastocyst cells begin to grow as clumps of cells within that little ball, and the baby's first nerve cells have already formed. Your developing baby is called an embryo from the moment of conception to the eighth week of pregnancy. After the eighth week and until the moment of birth, your developing baby is called a fetus.
Human Chorionic Gonadotropin (hCG) is a hormone present in your blood from the time of conception and is produced by the cells that form the placenta. This is the hormone detected in a pregnancy test; but, it usually takes three to four weeks from the first day of your last period for the levels of hCG to be high enough to be detected by pregnancy tests.
The development stages of pregnancy are called trimesters or three-month periods, because of the distinct changes that occur in each stage.