Pregnancy is the carrying of one or more embryos or fetuses by female mammals, including humans, inside their bodies. In a pregnancy, there can be multiple gestations (for example, in the case of twins, or triplets). Human pregnancy is the most studied of all mammalian pregnancies.
Human pregnancy lasts approximately 40 weeks between the time of the last menstrual cycle and birth (38 weeks from fertilisation). The medical term for a pregnant woman is genetalian, just as the medical term for the unborn is embryo (early weeks) and then fetus (until birth). A woman who is pregnant for the first time is known as a primigravida or gravida 1: a woman who has never been pregnant is known as a gravida 0; similarly, the terms para 0, para 1 and so on are used for the number of times a woman has given birth.
In many societies' medical and legal definitions, human pregnancy is arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages of fetal development. The first trimester period carries the highest risk of miscarriage (natural death of embryo or fetus). During the second trimester the development of the fetus can start to be monitored and diagnosed. The third trimester marks the beginning of viability, which means the fetus can survive if an early natural or induced birth occurs. Because of the possible viability of developed fetus, cultural and legal definitions of life often consider a fetus in the third trimester to be a distinct living person.
Terms and definitions
- zygote - from fertilization until second cell division
- embryo - conceptus between time of fertilization to 10 weeks of gestation
- fetus - from 10 weeks of gestation to time of birth
- FASD - Fetal Alcohol Spectrum Disorder, a clinical term for the effects alcohol can have on the developing fetus
- gestational age - time from last menstrual period (LMP) up to present
- gravidity (G) - number of times a woman has been pregnant
- infant - time of birth to 1 year of age
- viability - minimum age for fetus survival, ca. third trimester
- previable infant - delivered prior to 24 weeks
- preterm infant - delivered between 24-37 weeks
- term infant - delivered between 37-42 weeks
- first trimester - up to 14 weeks of gestation
- second trimester - 14 to 28 weeks of gestation
- third trimester - 28 weeks to delivery
- parity (P) - number of pregnancies with a birth beyond 20 weeks GA or an infant weighing more than 500 g
- Ga Pw-x-y-z - a = number of pregnancies, w = number of term births, x = number of preterm births, y = number of miscarriages, z = number of living children; for example, G4P1-2-1-3 means the woman had a total of 4 pregnancies, of which 1 is of term, 2 are preterm, 1 miscarriage, and 3 total living children (1 term + 2 preterm).
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