Understanding the Science Behind Conception

Are you struggling to conceive? You are not alone – about 9 percent of men and 11 percent of women of reproductive age in the United States have had fertility problems, according to the National Institutes of Health. Infertility can have a number of causes. Understanding the science behind conception can help you recognize some of the factors affecting your fertility and may even increase your chances of conception.

The Science of Conception

Throughout the course of a month, the mucous membrane lining the uterus will thicken in preparation for the possible implantation of an embryo. This mucous membrane, known as the endometrium, protects the unborn baby and provides oxygen and nutrients. If the woman does not become pregnant, her body will shed the endometrium during her period.

The semen contains millions of sperm, which swim through the cervix and into the uterus. Once inside, the sperm navigate their way through the cervical mucus to find the fallopian tubes. Out of the millions of sperm cells produced, only a few hundred will make it this far and only one will fertilize the egg.

Each month, a woman’s ovaries release an egg, in a process known as ovulation. The egg can survive for up to 24 hours after ovulation. If the egg is not fertilized, the body will absorb it. When the egg is released, any sperm in the fallopian tube will swim towards it.

The egg is surrounded by a layer of cells called the corona radiata and a protective coating called the zona pellucida, which the sperm must penetrate to reach the egg. Once the sperm successfully penetrates the zona pellucida, a chemical reaction occurs that prevents any other sperm from entering. The sperm then fuses with the egg, and their genetic material combines to form a zygote.

The zygote divides rapidly as it travels down the fallopian tube towards the uterus, a journey that takes about 3-4 days. During this time, it continues to divide into more cells and forms a blastocyst. After the blastocyst reaches the uterus, it attaches to the uterine wall and begins to implant. This process takes about a week, and once it is complete, the blastocyst is officially considered an embryo.

The embryo continues to develop into a fetus, and eventually, into a baby. During this process, the fetus goes through many stages of development, including the formation of the brain, heart, and other vital organs.

Factors that Affect Fertility

Certain factors can affect the process of conception to make getting pregnant harder.


As women age, their fertility decreases. The decline in fertility becomes more significant after the age of 35.


Smoking can damage the fallopian tubes and cause hormonal imbalances that can make it difficult to conceive. Alcohol consumption can also affect fertility, as excessive drinking can disrupt hormone levels and decrease sperm count in men. Obesity can cause hormonal imbalances that can make it difficult to conceive.

Chronic stress

Ongoing stress can cause hormonal imbalances and interfere with ovulation, making it difficult to conceive.

Certain medical conditions

Polycystic ovary syndrome (PCOS) can cause irregular periods, hormonal imbalances, and cysts on the ovaries, making it difficult to conceive. Endometriosis occurs when tissue similar to the lining of the uterus grows outside of the uterus, causing inflammation and scarring that can interfere with conception. Thyroid disorders, autoimmune disorders, and sexually transmitted infections (STIs) can cause hormonal imbalances, inflammation, and damage to the reproductive system.

Uterine fibroids can physically prevent the embryo from implanting into the uterus. Scar tissue and adhesions in the endometrium from previous surgeries and infections can cause the uterus to reject embryos.

Environmental factors

Exposure to certain chemicals and toxins, such as pesticides and lead, can interfere with hormone levels and damage the reproductive system, making it difficult to conceive. Exposure to high levels of heat can affect fertility in men by decreasing sperm count and motility.

Conceiving, carrying and delivering a baby is a complex physiological process, and there are many factors that can affect your ability to conceive. For more information and for personalized reproductive care, contact Viera Fertility Center.