Human pregnancy lasts approximately 9 months between the time of the last menstrual cycle and childbirth  weeks from fertilisation. In many societies medical and legal definitions, human pregnancy is somewhat arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages of fetal development. Though these are the averages, the actual length pregnancy depends on various factors. This allows the blastocyst to receive vital nutrients from the woman. In the post-implantation phase, the shirt manufacturers in china blastocyst secretes a hormone named human chorionic gonadotropin which in turn, stimulates the corpus luteum in the woman's ovary to continue producing progesterone. The beginning of pregnancy may be detected in a number of ways, including various pregnancy tests which detect hormones generated by the newly-formed placenta.

This is used to calculate the Estimated Date of Delivery. Approximately 3. Babies born before the 37 week mark are considered premature, while babies born after the 43 week mark are considered postmature. But it is not clear whether this refers to the due date calculated from an early sonograph or from the last menstruation (see further down). Counting from the beginning of the woman's last menstrual cycle, the norm is 40 weeks (the basis for Naegele's rule).6% of all women deliver on the due date predicted by LMP, and 4. However, a pregnancy is considered to have reached term between 37 and 43 weeks from the beginning of the last menstruation. In a pregnancy, there can be multiple gestations (for example, in the case of twins, or triplets).

This is 38 weeks, or approximately 8 Gregorian months and 22. According to the same reference, less than 10% of births occur on the due date, 50% of births are within a week of the due date, and almost 90% within two weeks. During the second trimester the development of the fetus can start to be monitored and diagnosed. An accurate date of fertilization is important, because it is used in calculating the results of various prenatal tests (for example, in the triple test). Before pregnancy begins, a female oocyte egg must join, by male spermatozoon in a process referred to in medicine as "fertilisation", or commonly though perhaps inaccurately)as "conception. Home pregnancy tests are personal urine tests, which normally cannot detect a pregnancy until at least  days after fertilization." In most cases, this occurs through the act of sexual intercourse, in which a man ejaculates inside a woman, thus releasing his sperm. The first trimester period carries the highest risk of miscarriage (natural death of embryo or fetus). The medical term for a pregnant woman is genetalian, just as the medical term for the potential baby is embryo early weeks and then fetus until birth.

Clinical blood and urine tests can detect pregnancy soon after implantation, which is as early as 6-8 days after fertilization. Human pregnancy is the most studied of all mammalian pregnancies. According to Merck, the norm for human pregnancy is that it lasts 266 days from the date of fertilization. A decision may be made to induce labour if a baby is perceived to be overdue.7% give birth on the day predicted by ultrasound. For example, the first pregnancy tends to last longer than subsequent pregnancies.Pregnancy is the carrying of one or more embryos or fetuses by female mammals, including humans, inside their bodies. Pregnancy tests detect the presence of human chorionic gonadotropin. The third trimester marks the beginning of viability, which means the fetus might survive if an early birth occurs.Though pregnancy begins at implantation, it is often convenient to date from the first day of a woman's last menstrual period. Both clinical and home tests can only detect the state of pregnancy, and cannot detect its age. A woman who is pregnant for the first time is known as a primigravida or gravida  a woman who has never been pregnant is known as a gravida  similarly, the terms para 0, para 1 and so on are used for the number of times a woman has given birth. The glands in the lining of the uterus will swell in response to the blastocyst, and capillaries will be stimulated to grow in that region.