Fertilization

The process that typically occurs within hours or days after sexual intercourse, sperms are released by ejaculation in vagina taking their way from cervix to uterus, then reach fallopian tubes. One or rarely two sperm unite the ovum under a number of biological interactions, which is called fertilization, combining their genetic materials together in one of the woman's two fallopian tubes (Rt or/ Lt). Ideal timing for fertilization to happen is a window time of synchronization of the lives of the two gametes ( sperm & egg ), as sperm can live inside the female reproductive tract for up to 5 days after ejaculation, while ovum ( egg ) can be fertilized at the period between 12 to 24 hours after egg releasement to fallopian tube by ovulation process.

The resulted union or single celled organism presents the first cell of the fetus and is named Zygote, which travels to uterus to implant in the uterine lining and mark a potential pregnancy. If implantation succeeds, pregnancy is considered to occur. If implantation fails, pregnancy does not occur, leading to a menstrual period.

Information resources

• Concluded from Google knowledge graph, the scientific content released by scientific web platforms including Pregnancy, Birth and Baby, Natural Cycles, Bocah Indonesia, Ceveland Clinic, March of Dimes and Verywell Health.
• Concluded from Gemini tool edition on date 12 September 2025; for the features of sperm pathway, the fertilization timing, and the nature of zygote.

According to the writer's conclusion of September 2025 for the writings of Encyclopaedia Britannica Article History editors, in biological terminology, sperm and egg (ovum) are known as human gametes, generally called human sex or reproductive cells, each of them is described as haploid cell; having only one set of single chromosomes ( 23 chromosome ), half the genetic material necessary to form a complete organism. During fertilization, the two gametes fuse together to form the diploid zygote which has paired chromosomes ( 23 pairs of chromosomes ), the complete genetic material that generates fetus.

According to writer's conclusion on 26 September 2025 for Slon, Pedro (2019) "Defining the Biological Identity of the Unborn: A Scientific Approach to The Human Zygote," JCCC Honors Journal: Vol.10: Iss.2, Article 1, resource : Dr Mark Hill 2019, UNSW Embryology and US National Library of Medicine, merely 30 minutes after fertilization, zygote prevents polyspermy that means more sperms coming in to fertilize the egg after its first fertilization. This prevention occurs due to the very specific proteins produced through a lot of intricate processes and changes in the formed zygote. The definition of an organism can be applied to the human zygote as it takes a functioning and a developing life course different from that of both gametes, having the genes code nessecary for cell divisions, differentiations, and proliferations into major organs and tissues. The produced cell groups of the developing zygote start forming the destinctive tissues of the heart, the brain, and the spinal cord in their specific locations at around only the 3rd week of pregnancy, the 5th week of gestation. 

Later edition extracted from other resources including CK-12, Kenyon college, Vita altera, Taylor & Francis, NCBI, and Mount Sinai states that prevention of polyspermy is complete much faster than 30 minutes, beginning almost immediately within seconds to minutes after the first sperm-egg fusion through a fast block; presented in depolarization of the egg's membrane within seconds of the first sperm entry and this temporarily repels other sperms. And through a slow block; occurring over the next 10 - 15 minutes and is presented in the enzymes released from cortical granules located beneath the egg membrane inducing a permanent modification in the zona pellucida (the outer layer) which makes it hard and impenetrable.

• Cardiac output increases as a result of heart rate and stroke volume increasing. This normally happens to support fetal development.

• Blood pressure remains normal during 1st trimester, then decreases during 2nd trimester due to the increase in arteriovenous shunts of placenta, the decrease in peripheral resistance, and the common synchronizing hydremia, then returns back to normal by the 3rd trimester. Normal pregnancy generally marks a normal or a slight drop in blood pressure, so any increase in blood pressure reaching a level of 140/90 mmHg is considered abnormal. If maternal BP reaches higher than 140/90 mmHg, we say that mother has pregnancy toxemia or pregnancy hypertensive disorders which are commonly happen during 3rd trimester, evoking significant symptoms like bilateral lower limb edema and proteinuria.

• Venous return decreases when there is a uterus compression (especially in supine position) on inferior vena cava causing a mild bilateral lower limb edema and varicosity. To release the compression on IVC, mother is recommended to sleep in a side-lying position on her left side. Venous return normally remains during pregnancy or even increases due to high blood volume, only interrupted in some cases like supine lying position.

• As a physiological (not pathological) change, maternal plasma volume increases while hemoglobin concentration decreases, which leads to hydremia and physiological anemia, normally happens in pregnant women to compensate the bad venous drainage and prevent coagulability disorders like DVT. In the previous light, most pregnant women are susceptible to iron deficiency anemia due to the increasing nutritional requirements synchronized by the decreasing intake and absorption.

Note : Author conclusion from reading a clinical evidence edition for the previous article set up by Gemini searching tool on 13 September 2025, stating that 

• "pregnancy toxemia" is an older, outdated term for the mentioned symptoms while those symptoms should be defining features of "Preeclampsia", a serious condition presenting one feature of pregnancy hypertensive disorders features. 

• The primary reason for plasma volume increasing is to accommodate the volume level needed for fetus, placenta (e.g. placental perfusion), and maternal organs, while bad venous drainage compensation is a secondary reason for plasma volume increasing.

General common symptom is presented in dyspnea due to the pregnancy synchronizing hyperventilation. This happens under the effect of the increased progesterone hormone releasement, in addition to the elevation of diaphragm especially during the 8th month of pregnancy.

Information resources

From academic information resources collected by the writer's studies of academic content released by the side of Faculty of Physical Therapy Cairo University 2024 - 2025, by lecturer Dr. Adel - GYNA Medicine.

14 September 2025 releasement conclusion, according to the writer's studies of academic content released by the side of Faculty of Physical Therapy Cairo University 2024 - 2025, by Dr. Adel, lecturer of GYNA Medicine. States that Symptoms which are commonly appear include 

Amenorrhea : Means that period is missed. Considered to be the most important symptom for pregnancy. 

Frequency of micturition : Reasons like congestion, and irritation of bladder.

Morning sickness : Symptoms like nausea and some times vomiting especially in the morning.

Breast symptoms : Like enlargement, tenderness, discomfort and the tingling sensation.

Appetite changes : This happens due to normal or pathological changes of pregnancy. 

29 September 2025 releasement conclusion, according to the writer's studies of academic content released by the side of Faculty of Physical Therapy Cairo University 2024 - 2025, by Dr. Adel, lecturer of GYNA Medicine.

• Breast

Size and vascularity of breast are increased with the breast felt nodular and tender, veins are visible dilated, pigmentation of nipple and primary areola is increased, secondary areola appears, montgomery tubercles appear around areola, and expression of colostrum which is rich in proteins and minerals while poor in fats and sugar.

• Pelvis 

Vulva and vagina present a blue or violet color at the 8th week with increased pulsations in the lateral fornix. Uterus presents enlargement, softness, and globular shape.

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Last updated on 2/October 2025.