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Chance of fertilization by menstrual cycle day relative to ovulation [15] Pregnancy rates for sexual intercourse are highest during the menstrual cycle time from some 5 days before until 1 to 2 days after ovulation. [16] For optimal pregnancy chance, there are recommendations of sexual intercourse every 1 or 2 days, [17] or every 2 or 3 days. [18]
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.
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 ]
Nine-week-old human embryo from an ectopic pregnancy. Organogenesis is the development of the organs that begins during the third to eighth week, and continues until birth. Sometimes full development, as in the lungs, continues after birth. Different organs take part in the development of the many organ systems of the body.
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.
Fertilization was not understood in antiquity. Hippocrates believed that the embryo was the product of male semen and a female factor. But Aristotle held that only male semen gave rise to an embryo, while the female only provided a place for the embryo to develop, [5] a concept he acquired from the preformationist Pythagoras.
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The World Health Organization (WHO) describes the postnatal period as the most critical and yet the most neglected phase in the lives of mothers and babies; most deaths occur during the postnatal period. [62] Following the birth, if the mother had an episiotomy or a tearing of the perineum, it is stitched.