Alternatively there are mobile apps, which essentially always give consistent estimations compared to each other and correct for leap year, while pregnancy wheels made of paper can differ from each other by 7 days and generally do not correct for leap year.Furthermore, actual childbirth has only a certain probability of occurring within the limits of the estimated due date. A study of singleton live births came to the result that childbirth has a standard deviation of 14 days when gestational age is estimated by first trimester ultrasound, and 16 days when estimated directly by last menstrual period. Physiology
Capacity
Fertility and fecundity are the respective capacities to fertilize and establish a clinical pregnancy and have a live birth. Infertility is an impaired ability to establish a clinical pregnancy and sterility is the permanent inability to establish a clinical pregnancy.The capacity for pregnancy depends on the reproductive system, its development and its variation, as well as on the condition of a person. Women as well as intersex and transgender people who have a functioning female reproductive system are capable of pregnancy. In some cases, someone might be able to produce fertilizable eggs, but might not have a womb or none that can sufficiently gestate, in which case they might find surrogacy. Initiation
Through an interplay of hormones that includes follicle stimulating hormone that stimulates folliculogenesis and oogenesis creates a mature egg cell, the female gamete. Fertilization is the event where the egg cell fuses with the male gamete, spermatozoon.
Gradually, portraits of pregnant women began to appear, with a particular fashion for "pregnancy portraits" in elite portraiture of the years around 1600. Pregnancy, and especially pregnancy of unmarried women, is also an important motif in literature. Notable examples include Thomas Hardys 1891 novel Tess of the dUrbervilles and Goethes 1808 play Faust. See also
Couvade syndrome
Cryptic pregnancy
False pregnancy
Simulated pregnancy

References
Further reading
External links

Pregnancy at Curlie
Merck Manual Home Health Handbook – further details on the diseases, disorders, etc., which may complicate pregnancy. Pregnancy care – NHS guide to having a baby including preconception, pregnancy, labor, and birth.