Pregnancy is the state of being pregnant.
In general (albeit not always), the female of a mammalian species, after either sexual intercourse, assisted reproduction (e. g. in vitro fertilization) or the implantation of an embryo after cloning, carries one or more offspring.
Human pregnancies typically last about 39 weeks, resulting in a live birth or births. The gestational period is divided into three 13-week-long trimesters. A female gamete, known as an egg is fertilized by a male gamete, a sperm. The fertilized egg then implants in the uterine wall. After about 36 hours, the fertilized egg is called an embryo. After about eight weeks, the embryo is known as a fetus, and is referred to as that until birth.
Premature birth is not uncommon and is no longer uniformly fatal to the child. However, the length of a pregnancy can be directly correlated to a child's chances of surviving.
On Aris, Arisian males allowed the females to die out once they were able to reduce the amount of time of a pregnancy down to zero days. This was accomplished as a result of institutional sexism. Once the NX-01 made contact and the Arisians met Hoshi Sato, they stole some of her female hormones in order to rebuild the females of their species (In Between Days: There's Something About Hoshi).
Calafan women typically were considered to be sexually mature and marriageable by age sixteen. This included the taking of a nocturnal lover, only accessible via Psionic connection (In Between Days: Together).
Daranaean females had pregnancies lasting a short six months, and then the child would be placed into the mother's abdominal pouch for another six months, until emergence. During their time in the pouch, they were known as pouchlings. Daranaean children could refer to two separate birthdays, one for birth and the other for pouch emergence (In Between Days: Take Back the Night).