Pregnancy 101 | National Geographic

(elegant piano music) – [Narrator] The product of
millions of years of evolution, the human body is capable
of many remarkable things, but none of which may
be quite so incredible as the development of life in utero. (calm music) Over three million babies are born each year in the United States alone. Worldwide, the highest
fertility rate is found in Niger, where the
average woman gives birth to approximately 6.49
children in her lifetime. Singapore sits on the
opposite end of the spectrum at just 0.83, less than
one birth per woman. While the number of births, customs, and traditions vary
from culture to culture, the developmental process
is essentially universal. Derived from the Latin word praegnantem, meaning before birth,
pregnancy is the period in which the fetus
develops inside the womb. Typically lasting around 40 weeks, human pregnancies are divided into three trimesters
of three months each. (calm music) Pregnancy begins in the uterus, where a sperm fertilizes an egg. If the sperm carries an X chromosome, the baby will become female, while a Y chromosome will result in the baby becoming male. The fertilized egg, or zygote, divides repeatedly as it travels through the fallopian tube, implanting itself on the uterine wall to form both the embryo and a specialized organ
known as the placenta. Found only in eutherian,
or placental, mammals, the placenta will manage waste
and provide key nutrients, oxygen, and hormones
via the umbilical cord. The brain, which will continue to grow and develop
throughout the pregnancy, makes up nearly half of the
embryo in these early stages. As the eyes, nose, ears, and mouth, along with all major organs continue to develop in month three, the baby will begin to look more and more human with each passing day. The second trimester lasts
from weeks 13 through 27. The fetus will more than double in size during this time, and soon, its movements may be felt by the mother. Hearing first develops around week 18, but the fetus will not respond to sounds outside of the womb until
approximately week 25. Starting at week 28 and
lasting up until delivery, the third trimester is a
time for final touches, such as eyelashes and taste buds. (light music) With most major development complete, the fetus will gain nearly
half a pound a week. To make room for this rapid growth, the mother’s internal
organs adjust significantly throughout the pregnancy. Dropping lower into the pelvis, a fetus typically turns heads-down in preparation for birth. Most bones will have
hardened by this time, though the skull will
remain relatively soft to ease the delivery process. Labor is divided into stages, beginning with the dilation of the cervix and resulting in the delivery of both the baby and the placenta. Despite thousands of years
of human pregnancies, scientific understanding
has only recently begun to catch up, leading to
an increase in success and safety for both mother and child. As our understanding of
pregnancy continues to develop, so do technology and
reproductive medicine, with much more in store for
the future of pregnancy.

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