THE PROCESS OF FERTILIZATION
Fertilization
This is the fusion of the male and female gametes, which results in the formation of a zygote
This process usually takes place in the ampulla of the fallopian tubes.
In humans, fertilization is completed within 20 hours.
Implantation
At about 6 days after ovulation blastocyst implants – orients cell mass toward endometrium, and secretes enzymes which allow it to penetrate (digest) the endometrial wall. This nourishes the blastocyst for about a week after implantation.
As early as 8 -12 days after fertilization, the blastocyst begins to secrete human chorionic gonadotropin or hCG.
hCG keeps the corpus luteum active until the placenta can produce estrogens and progesterone.
The presence of hCG is the basis for pregnancy tests.
Gestation period
Divided into three trimesters.
During first trimester individual starts out as a zygote, then morula, blastocyst, and after implantation, is called an embryo.
Embryonic phase of development lasts from fertilization until the 8th week of gestation, when it becomes a fetus.
By day 35 the heart is beating, and eye and limb buds are present.
By month four, the rudiments of all organ systems are formed and functioning, and from then on, fetal development is primarily a matter of growth.
By the end of the third month the placenta is functioning
The placenta formation • The trophoblast is characterized by its invasiveness that provides attachment to the endometrial tissue. Differentiation of trophoblasts results into cytotrophoblasts and syncytiotrophoblast.
• The placenta is formed from the syncytiotrophoblast and is complete by 12 weeks.
The foetus develops from the inner cell mass and organogenesis is almost complete by 12 weeks
Functions of the placenta:
1 Transfer gasses
2 Transport nutrients
3 Excretion of wastes
4 Hormone production – temporary endocrine organ – estrogen and progesterone
5 Formation of a barrier – incomplete, nonselective – alcohol, steroids, narcotics, anesthetics, some antibiotics and some organisms can cross
The Whole Period of Pregnancy Can Be Divided Into Three Stages:
The first trimester (early pregnancy): 1-13w
The second trimester (mid pregnancy): 14-27 w
The third trimester (late pregnancy): 28-40w
The Diagnosis of the First Trimester
The first trimester (early pregnancy): 1-13w
1. History and symptoms
A. Cessation of menstruation (amenorrhea)
This is the first frequent symptom of pregnancy, although a few women may have slight bleeding after conception. But amenorrhea could be due to other reasons which must be ruled out.
B. Nausea and vomiting
Also called morning sickness because they occur upon arising. These symptoms appear one or two weeks after the period is missed and last until 10th to 12th week, its severity varies from mild nausea to persistent vomiting (e.g. Hyperemesis gravidarum).
C. Urinary symptoms
Increased frequency of urination is due to increased circulation associated with the effect of estrogen and progesterone on the bladder, combined with pressure by the gradually enlarged uterus on the bladder.
2. Signs
Breast changes
Breast enlargement and vascular engorgement. Nipple and areola become blacker. Enlargement of the accumulated sebaceous glands of the areolas (Montgomery’s tubercles) may be noted.
Changes of the reproductive organs
Vagina:The vaginal wall become discoloration as the pelvic blood vessel becomes congested.
Cervix: Cyanosis and a gradual softening due to congestion.
Changes of the reproductive organs
Uterus: enlargement and softening. After the 12th week, the fundus of the uterus is usually palpable above the symphysis pubis.
Pregnancy test
The laboratory test for pregnancy are based on the identification of human chorionic gonadotropin (hCG), which can be detected as early as 7-9 days after fertilization by high sensitive technique. The samples may be blood or urine.
Ultrasonography
There are trans-vaginal and abdominal Ultrasonagraphys.
A gestational sac can usually be identified at 5-6 weeks after the beginning of the last period.
Ultrasonography
Fetal heart beating can be detected by about 7th week and the fetus itself can be seen by about the 8th week.
Doppler is also an ultrasound technique, which diagnoses the pregnancy by revealing the heart beating.
References
1. Chwalisz K, Gardiel R E ,regulation of the uterus and cervix during pregnancy and lactation, role of progestrone and nitric oxide Ann M Y accad Sc 828 238 ,1997.
2. Arthur C Guyton Textbook of Medical Physiology Tenth Edition.
3.www. Google engine search
4. Williams Obstetrics 23rd edition 2010 The McGraw Hill companies Inc.
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