The medical community divides the fetal growth and
development stages (which occur during pregnancy) into three trimesters. A completely
full-term pregnancy lasts a total of 40 weeks, and these 40 weeks are divided into three
trimesters which each denote a period of significant milestones, characteristics, and
development for the fetus.
The first 12 weeks of pregnancy
are also known as the first trimester of pregnancy. However, the developing embryo will
not be known as a “fetus” until after around the 10th week of gestational development.
The embryonic stage precedes the fetal development stage. By the end of the 10th week of
gestation, the basic formations for the organs have been established, and the embryo has
entered the fetal stage of development.
During this time of
beginning fetal stage of development, the heartbeat can be heard with a Doppler
stethoscope and the heart can be seen beating during an ultrasound examination. Other
characteristics of this stage include: Urine secretion from the kidneys, teeth buds,
more developed eyelids, more distinctive face formation, more defined external ear
formation, and red blood cell production in the liver.
The
second trimester of pregnancy occurs during weeks 13 through 27. (Be aware that
different charts may vary slightly in the exact amount of weeks that determine each
trimester). During this second trimester, fetal development includes: Sexual
differentiation, harder bones, finger and toe nail development, liver and pancreatic
fluid secretions, continued formation of foot and fingerprints, and Lanugo (fine hairs
that cover the fetus).
The third and final trimester of
pregnancy is roughly weeks 28 through 40. Fetal development during this stage includes:
More complex brain connections, increase in body fat, iron and calcium storage,
sensitivity to light, tear production, eye movements, fully developed hearing, and body
temperature regulations.
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