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Humans, unlike most other species, have concealed ovulation, a lack of obvious external signs to signal estral receptivity at ovulation (i.e., the ability to become pregnant). Some species of animals with estrous cycles have unmistakable outward displays of receptivity, ranging from engorged and colorful genitals to behavioral changes like ...
Most — if not all — of these changes are due to pregnancy hormones, such as estrogen, progesterone, and human chorionic gonadotropin. Previous research shows that pregnancy hormones can also ...
Pregnancy (mammals) A pregnant lioness. In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once it leaves the uterus.
Superfetation. Superfetation (also spelled superfoetation – see fetus) is the simultaneous occurrence of more than one stage of developing offspring in the same animal. [1][2][3] In mammals, it manifests as the formation of an embryo from a subsequent menstrual cycle, while another embryo or fetus is already present in the uterus.
Interspecific pregnancy (literally pregnancy between species, also called interspecies pregnancy or xenopregnancy) [1] is the pregnancy involving an embryo or fetus belonging to another species than the carrier. [1] Strictly, it excludes the situation where the fetus is a hybrid of the carrier and another species, thereby excluding the ...
The menstrual cycle is the monthly process by which the body prepares for the possibility of pregnancy. The length of the menstrual cycle will vary from person to person. The average cycle lasts ...
Some teratomas can even become primitive fetuses (fetiform teratoma) with imperfect heads, limbs and other structures, but are non-viable. In 1995, there was a reported case of partial human parthenogenesis; a boy was found to have some of his cells (such as white blood cells) to be lacking in any genetic content from his father. Scientists ...
Gestation, called pregnancy in humans, is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta , which is attached to the fetus' abdomen via an umbilical cord .