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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.
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]
In human pregnancy, prenatal development is also called antenatal development. The development of the human embryo follows fertilization , and continues as fetal development . By the end of the tenth week of gestational age , the embryo has acquired its basic form and is referred to as a fetus .
In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres .
Pregnancy is the time during which one or more offspring develops inside a woman's uterus (womb). [4] [13] A multiple pregnancy involves more than one offspring, such as with twins. [14] Pregnancy usually occurs by sexual intercourse, but can also occur through assisted reproductive technology procedures. [6]
Diagram of the human fetal circulatory system. Oxygenated blood from the placenta is carried to the fetus by the umbilical vein, which will drain into the inferior vena cava (IVC) through the ductus venosus or the liver. [ 5 ]
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Adactylidium is a genus of mites known for its unusual life cycle. [1] An impregnated female mite feeds upon a single egg of a thrips, rapidly growing five to eight female offspring and one male in her body. The single male mite mates with all his sisters when they are still inside their mother.