Weight at birth
A more complex and long process takes place inside the fetus. A fetus with unformed sexual characteristics has two pipe systems: Mullerian and Wolff ducts. But in the female fetus, the wolf tubes between the 7th and 9th weeks practically disappear, while the lower Muller tubes combine to form the vagina. Then during the slower process, by the 34th week, the undifferentiated sex glands (gonads) turn into primitive ovaries, and the upper Muller tubes become fallopian tubes. At the boy, on the contrary, Mullerian pipes disappear. The gonads move into the scrotum and become the testicles, and each Wolf tube turns into the seminal duct.
Human development in the uterus occurs faster than ever after birth. The figure (see pp. 12–13) shows a proportional increase in the average fetus every 4 weeks. As it grows, the fetus moves and changes its position in the uterus.
A baby carrier weighs less than 1 g, a baby blue whale weighs almost 10 tons. A newborn survives a wide range of weights from 0.9 to 13 kg, but is best when the baby is born with an average weight of 3.4 kg. The average weight of boys is slightly higher (3.4 kg), girls - lower (3.2 kg).The heart and lungs of a newborn boy are slightly larger than those of a girl, and the liver weighs slightly less.
With unusually early childbirth, the birth rate of boys is higher, and with unusually late - just over girls.
However, the prematurity of the child is determined not by the duration of the pregnancy, but by the weight of the newborn. In this regard, as “premature”, girls are more often qualified as girls, since their greater percentage has a weight of less than 2.5 kg. However, in reality they are “full-term newborns with low weight”.
Newborns whose weight in one direction or another is very different from; average, have less chance of survival. Mortality among newborns with an average weight is 2%, among infants weighing 2.7 or 4.1 kg - 3%, and among those weighing 2 or 4.8 kg - 10%. Among the surviving babies with a weight that is very different from the average, the probability of physical defects is greater.
In perfectly normal children, the pace of development can vary considerably. A child can start sitting for a few moments without support between 5 months and a year at any time, and can walk without assistance between 8 months and 4 years. Parents should not think that such delays are serious or that they can have long-term consequences.
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