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If the testicles remain too close to the body, it is likely that the increase in temperature will harm the spermatozoa formation, making conception more difficult. This is why the testes are carried in an external scrotum rather than within the abdomen; they normally remain slightly cooler than body temperature, facilitating sperm production.
Adequate nutrition is needed for a healthy fetus. Mothers who gain less than 20 pounds during pregnancy are at increased risk for having a preterm or low birth weight infant. [51] Iron and iodine are especially important during prenatal development. Mothers who are deficient in iron are at risk for having a preterm or low birth weight infant. [52]
A newly developing human is typically referred to as an embryo until the ninth week after conception, when it is then referred to as a fetus. In other multicellular organisms, the word "embryo" can be used more broadly to any early developmental or life cycle stage prior to birth or hatching .
Final weight gain takes place during the third trimester; this is the most weight gain throughout the pregnancy. The woman's abdomen will transform in shape as the fetus turns in a downward position ready for birth. The woman's navel will sometimes become convex, "popping" out, due to the expanding abdomen. The uterus, the muscular organ that ...
In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult body has been developed. Until the ...
1 - morula, 2 - blastula 1 - blastula, 2 - gastrula with blastopore; orange - ectoderm, red - endoderm. Embryology (from Greek ἔμβρυον, embryon, "the unborn, embryo"; and -λογία, -logia) is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos and fetuses.
For example, if there is a gestational age based on the beginning of the last menstrual period of 9.0 weeks, and a first-trimester obstetric ultrasonography gives an estimated gestational age of 10.0 weeks (with a 2 SD variability of ±8% of the estimate, thereby giving a variability of ±0.8 weeks), the difference of 1.0 weeks between the ...
Low birth weight is a concern for medical providers due to the tendency of these infants, described as "premature by weight", to have a higher risk of secondary medical problems. X-rays are known to have possible adverse effects on the development of the fetus, and the risks need to be weighed against the benefits.