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A typical precocial mammal has a gestation period almost four times longer than a typical altricial mammal of the same body size. [20] Precocial mammal species generally have greater adult body weights than altricial mammals as precocial mammals have markedly longer gestation periods than altricial mammals. [21]
The mean pregnancy length has been estimated to be 283.4 days of gestational age as timed from the first day of the last menstrual period and 280.6 days when retrospectively estimated by obstetric ultrasound measurement of the fetal biparietal diameter (BPD) in the second trimester. [12]
The term metrorrhagia is often used for irregular menstruation that occurs between the expected menstrual periods. [9] [10] Oligomenorrhea is the medical term for infrequent, often light menstrual periods (intervals exceeding 35 days). [11] Polymenorrhea is the medical term for cycles with intervals of 21 days or fewer.
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The proestrus is relatively long at 5 to 9 days, while the estrus may last 4 to 13 days, with a diestrus of 60 days followed by about 90 to 150 days of anestrus. Female dogs bleed during estrus, which usually lasts from 7–13 days, depending on the size and maturity of the dog.
Biologically, pregnancy starts at implantation of the fertilized egg. Human pregnancy can be divided into three trimesters, each approximately three months long: the first, second, and third trimester. The first trimester is from the last menstrual period through the 13th week, the second trimester is 14th–28/29th week, and the third ...
The first ten weeks of gestational age is the period of embryogenesis and together with the first three weeks of prenatal development make up the first trimester of pregnancy. From the 10th week of gestation (8th week of development), the developing embryo is called a fetus.
Blood and urine tests can detect pregnancy by 11 and 14 days, respectively, after fertilization. [77] [78] Blood pregnancy tests are more sensitive than urine tests (giving fewer false negatives). [79] Home pregnancy tests are urine tests, and normally detect a pregnancy 12 to 15 days after fertilization. [80]