Key stages of pregnancy from fertilization to full term

A woman’s health and well-being before and during pregnancy is vitally important to the life-long health of her embryo or fetus. Doctors can detect pregnancy as early as 8 or 9 days after fertilization.1 Most women, however, have no idea they are pregnant for weeks! These terms describe stages, events, and time periods during pregnancy and early human development. The uterus is a small, muscular structure which, in the event of pregnancy, serves to house, nourish, and protect the embryo and fetus until birth and then expel the fetus during childbirth.24 The size of the adult uterus varies widely depending on pregnancy status.
Following ovulation, during the Secretory Phase, theca cells and granulosa cells in the mature follicle transform to produce significant quantities of progesterone59 into the blood and the follicle is called a corpus luteum.60 The purpose of this hormone production is to further prepare and maintain the uterine lining for implantation in the event that fertilization occurs.
If fertilization does not occur, the Menstrual Phase begins as the corpus luteum begins to degenerate, progesterone and estrogen levels fall dramatically, and the uterine lining separates and is expelled from the uterus. The specialized function of the spermatozoon will be discussed briefly in the next unit as we review fertilization. It has begun to produce the pregnancy hormone hCG, which tells your ovaries to stop releasing eggs.Read about your pregnancy at 3 weeks. His skin is still translucent, but his tiny limbs can bend and fine details like nails are starting to form.Your baby is the size of a kumquatRead about your pregnancy at 10 weeks.

And for many moms-to-be, early pregnancy symptoms like morning sickness and fatigue have faded away.
By the time a woman discovers she is pregnant, many important structures in the growing embryo have long since developed. From fertilization through old age, this process (and our health) is impacted by our personal choices, the choices of those around us, and our environment. Investing the time and effort to master these basic terms and definitions will prepare you to understand the descriptions that follow and enable you to explain them to others. For example, the adult uterus prior to a first pregnancy measures about 6 to 8 centimeters in length and weighs about 70 grams. The myometrium is 12 to 15 millimeters thick,30 makes up the vast majority of the uterine wall, and expands greatly during pregnancy.
In the human embryo, about 1000 to 2000 primary germ cells34 travel to the developing ovaries from the yolk sac (See UNIT 5) during the 5th week of embryonic development.35 They form oogonia which divide by mitosis until midpregnancy.
In the absence of fertilization, by about 12 days after ovulation, the corpus luteum begins to degenerate, hormone levels fall, and the corpus luteum becomes nonfunctional.
Spermatogonia develop from primary germ cells which travel to the developing testes from the yolk sac (See UNIT 5) during the 5th week of embryonic development.70 They remain inactive until perhaps 12 or 13 years of age, when the process of sexual maturity called puberty occurs.

Chemical entities near the surface of the uterine tube wall remove several substances from the membrane overlying the acrosome. The cervix develops thick mucous which effectively closes the cervical canal from the vagina.67 All these events prepare the uterus for the possibility of fertilization and then implantation.
Everything from what she eats and drinks to what substances she uses plays a role in how her fetus develops. For this reason, a woman who has even the slightest possibility of becoming pregnant should already be thinking about how her lifestyle choices affect pregnancy.
Because the prenatal period is a time of preparation, pregnant women who avoid exposing themselves and their fetuses to harmful substances promote a lifetime of health for their children.
The cervix refers to the lower third of the uterus and is separated from the body by a narrowing called the isthmus.

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