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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]
Directly calculating the days since the beginning of the last menstrual period; Early obstetric ultrasound, comparing the size of an embryo or fetus to that of a reference group of pregnancies of known gestational age (such as calculated from last menstrual periods) and using the mean gestational age of other embryos or fetuses of the same size ...
Labor is separated into 4 stages. The first stage involves latent phase and active phase separated by the dilation of the cervix for 6 to 10 cm. The second stage is the pushing stage. The third stage involves the delivery of the placenta. And the last stage is the contraction of the uterus. [21]
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 trimester is 29/30th–42nd week. [6]
Second stage of labor starts when the cervix is dilated to 10 cm and finishes with the birth of the baby. This stage is characterized by strong contractions and active pushing by the mother. It can last from 20 minutes to 2 hours. [16] Third stage of labor starts after the birth of the baby and is finished when the placenta is delivered. [15]
Pregnancy usually occurs by sexual intercourse, but can also occur through assisted reproductive technology procedures. [6] A pregnancy may end in a live birth, a miscarriage, an induced abortion, or a stillbirth. Childbirth typically occurs around 40 weeks from the start of the last menstrual period (LMP), a span known as the gestational age.
The head comprises nearly half of the fetus' size. The face is well formed. The eyelids close and will not reopen until about the 27th week. Tooth buds, which will form the baby teeth, appear. The limbs are long and thin. The fetus can make a fist with its fingers. Genitals appear well differentiated. Red blood cells are produced in the liver.
Cannabis use during pregnancy was unrelated to risk of perinatal death or need for special care, but, the babies of women who used cannabis at least once per week before and throughout pregnancy were 216g lighter than those of non‐users, had significantly shorter birth lengths and smaller head circumferences.