4.2: Fertility and Conception

Learning Objectives

By the end of this section, you will be able to:

• Describe the components of fertility, both physical and psychosocial
• Describe the stages of conception, including ovulation and fertilization
• Describe the different causes of infertility

Human reproduction and conception have been celebrated in mythology, with symbols of female fertility evident in ancient civilizations all around the world. In addition, world mythology reflects the historical importance and need for fertility and reproduction in different cultures (Behjati-Ardakani et al., 2016). People as far back as 3500 BCE to 500 CE used the principles of insemination and “magic potions” in attempts to remedy childless royal families (Sharma et al., 2018). Though the stigma of infertility has largely changed and is still changing in some countries, the desire for a child remains strong for many people (Sharma et al., 2018). Infertility can be a life-changing experience for people. It affects both the body and mind and can completely alter a person’s relationship with their partner, family, and friends. It is important for nurses to consider both the physical and psychosocial components of fertility when working with people who are having difficulty in conceiving.

This section will address the concepts of fertility and infertility, including when patients should be advised to seek help, as well as the physical causes of and psychosocial factors involved with fertility. It will also delve into the diagnostic testing used to assess the fertility of both partners and the measures that can be used to improve fertility.

Components of Fertility

A person’s ability to conceive a pregnancy is called fertility. The inability to become pregnant after 1 year of regular sexual intercourse without using any form of birth control is called infertility (American College of Obstetricians and Gynecologists [ACOG], 2022b). It is a global health problem, affecting approximately 1 in 6 adults worldwide (World Health Organization, 2023b). This rate is fairly consistent across different regions and countries, and there is no significant difference between resource-poor and resource-rich countries. Global access to affordable reproductive care is lacking. In most cases, care is provided as an out-of-pocket expense, which can be financially devastating—or completely inaccessible—for people with limited resources.

Physical

Three factors are essential for pregnancy to occur: the release of an egg, the presence of sperm, and a healthy environment for implantation. Many factors can influence the health of the egg, sperm, and uterus. Environmental factors such as pesticides, radiation, and unclean water can cause difficulty with conception. Genetics, infections, and substance use can also affect fertility.

Egg

The egg, or ovum, is the female gamete, or reproductive cell, and contains one-half the number of chromosomes found in the body’s cells. Eggs are formed very early during the fetal development of female embryos, with nearly one million immature eggs (known as oogonia) present in the ovarian follicles at birth. That number decreases over the course of a person’s lifespan, with only 400,000 remaining by puberty (Krajnik et al., 2023).

When stimulated by follicle-stimulating hormone (FSH), the oogonium in the immature follicle undergoes mitosis to form a primary oocyte and a stem cell. Both new cells are genetically identical diploid cells, meaning that each contains the full 46 chromosomes (Hutter, 2023). The primary oocyte then undergoes the first meiotic division to form a secondary oocyte and a polar body. The second meiotic division causes the polar body to form two daughter polar bodies. The secondary oocyte forms a mature ovum and a third polar body. The result is three polar bodies and one mature ovum, all of which contain the haploid number of chromosomes (Figure 4.2).

Figure 4.2 Oogenesis The development of egg cells begins with the oogonia. These cells undergo several rounds of mitosis and meiosis to develop into a single ovum and three polar bodies. (credit: modification of “Oogenesis” by “Sciencia58”/Wikimedia Commons, CC0 1.0)

Sperm

Sperm cells are the male gametes or reproductive cells. Unlike the female gamete, sperm cells do not develop in the male body until after puberty in a process known as spermatogenesis. Each seminiferous tubule in the testes is lined with diploid cells, called spermatogonia, which contain the full 46 chromosomes and constantly undergo mitotic division. Some spermatogonia move away from the lining of the seminiferous tubule to mature and become primary spermatocytes. The primary spermatocytes undergo meiotic division to become two haploid (containing 23 chromosomes, instead of the usual 46) secondary spermatocytes. These secondary spermatocytes undergo a second round of meiosis to become four haploid spermatids, which eventually develop into four sperm cells (Figure 4.3). This entire process takes around 74 days (Komeya et al., 2018).

Figure 4.3 Spermatogenesis The development of sperm cells begins with immature spermatogonia. These spermatogonia undergo several rounds of mitosis and meiosis to develop into mature sperm cells in the testicles. (modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

These developing sperm cells move from the seminiferous tubules in the testicles into the head of the epididymis. They travel through the epididymis, from the head to the tail, over the course of about 12 days, where they absorb nutrients and testosterone (Figure 4.4). By the time they reach the tail of the epididymis, the sperm cells are mature and fully able to fertilize an ovum. These mature sperm cells are then stored in the epididymal tail until just before ejaculation. When this occurs, sperm cells leave the epididymis and rapidly travel through the vas deferens and internal duct system. They combine with fluid released from the seminal vesicles, the Cowper (bulbourethral) glands, and the prostate gland to create semen, a nutrient-rich fluid that nourishes the sperm cells. The semen enters the urethra near the base of the penis, where strong muscular contractions push the semen out of the body (Soni et al., 2022).

Figure 4.4 Movement of Sperm through the Male Reproductive System Developing sperm cells move from the seminiferous tubules to the epididymal tail before passing into the vas deferens and the other internal ducts in anticipation of ejaculation. (modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Each ejaculation releases up to 200 million sperm cells. If sperm cells are ejaculated into the vagina, they propel themselves through the cervix and into the female reproductive tract by rapid movements of the flagella, a long tail that protrudes from the end of the sperm cell. It takes sperm cells approximately 4 to 6 hours to travel to the fallopian tubes. Unlike egg cells, sperm cells can live up to about 5 days in the female reproductive tract (Conception: How it works, n.d.).

Without the presence of both viable sperm and eggs in the female reproductive tract at the same time, conception cannot occur.

Uterus

The final component needed for conception is the presence of a hormonally receptive uterus for implantation. During the menstrual cycle, the uterus undergoes several important changes in anticipation of a pregnancy. As the ovarian follicles enlarge, they begin to secrete estrogen. That estrogen signals the lining of the uterus, the endometrium, to proliferate and thicken. This is the proliferative phase of the uterine cycle.

After ovulation occurs and progesterone levels rise, the endometrium enters the secretory phase. The lining becomes even thicker and more vascular, which helps to prepare for the implantation of a fertilized egg, or zygote (Figure 4.5). If pregnancy does not occur, the endometrium begins to break down and slough off during menstruation, triggered by declining progesterone levels in the corpus luteum (Cable & Grider, 2023).

Figure 4.5 Endometrial Proliferation during the Menstrual Cycle The uterus undergoes significant development after ovulation as it prepares for implantation and possible pregnancy. (modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Even if ovulation perfectly coincides with sexual activity to result in a fertilized egg, pregnancy does not occur unless the zygote can properly implant in the uterine lining, triggering the hormonal cascade that occurs with pregnancy.

Psychosocial

Though conception and pregnancy are largely physiologic events, the nurse must not neglect the important psychosocial factors that are associated with fertility and conception. Stress and other societal pressure can impact both a person’s ability and their desire to conceive.

Societal Pressures

Social implications of fertility and reproduction extend beyond the individual and their family to the whole society, just as cultural and social change can affect the individual and their family makeup (Behjati-Ardakani et al., 2016). Likewise, changes in society have also impacted family-building practices in the United States and globally. People, for many different reasons, have opted to wait longer to start a family. “These changing fertility rates by age shifted the median age at which women gave birth in the United States from age 27 in 1990 to age 30 in 2019” (Morse, 2022). Several reasons for the delay in parenthood have been identified, including:

• a belief that assisted reproductive technologies could correct any fertility problems
• recognition that families could be formed through adoption
• not having a partner with whom to build a family
• not having the social support or financial stability in place to have children
• ambivalence toward wanting to have children
• more women focusing on building their career rather than starting a family
• lack of knowledge about how fertility declines with age (Delbaere et al., 2020).

Whatever the reason for delay, the effect of delayed childbearing is generally the same: Rates of fecundity decrease as the person assigned female at birth ages (Table 4.1). It is important to recognize that while the data about the effects of age on fertility are fairly consistent, they are an average. This means that one person may have significantly decreased fertility by the time they are 45, while another may have a similar decline by only 35 or 40 years of age.

Age of Patient in Years	Chance of Conception within 1 Year
<30	85%
30	75%
35	66%
40	44%

Table 4.1 The Odds of Conception within 1 Year Based on the Age of the Female Partner (Delbaere et al., 2020)

In 2018, a large systematic review of 71 studies found that many study participants reported low to moderate knowledge about age-related fertility decline (Pedro et al., 2018). Researchers found that interventions to increase this knowledge would be helpful, especially for men, persons with lower education, and family planning clinics (Pedro et al., 2018). The studies analyzed in this review found that these populations in particular were found to have lower knowledge about fertility and family planning (Pedro et al., 2018). Nurses working in family planning or women’s health settings should be aware of this knowledge gap and intervene as necessary.

Cultural Context

Falling Birth Rates

Many countries all over the world have been dealing with low birth rates for the past several years. Countries need, on average, a birth rate of at least 2.1 children per woman to maintain their population, yet the average birth rate in Europe is only 1.59 (BBC News, 2020), and it is as low as 0.78 in South Korea (Young & Bae, 2023). There are many reasons why people are choosing to not have as many children or to not have children at all:

• Strenuous work culture
• Poor wages
• Inflation and high cost of living
• Changing opinions about marriage (Young & Bae, 2023).

Scandinavia and France have seen success with increasing birth rates by increasing social benefits for families, including tax breaks, subsidized childcare and generous family leave. However, Scandinavia also began to see falling birth rates in recent years (BBC News, 2020), and similar policies were also not successful in South Korea (Young & Bae, 2023). More study is needed to determine what policy changes and social support systems are needed to improve birth rates moving forward.

(Young & Bae, 2023; BBC News, 2020)

Conception

Conception is a complex process, requiring several different precise processes. Ovulation, fertilization, and implantation must all occur safely. Factors can interrupt the process of conception, such as hormonal imbalances, structural abnormalities within the fallopian tube or uterus, or an inhospitable endometrium not allowing implantation. The quality of the egg and sperm can also affect conception. Timing of these processes must also be precise. When infertility occurs, health-care providers can examine these processes to potentially identify the cause of infertility.

Ovulation

Each month after menarche (the first menstrual period), a cyclic pattern of hormonal changes and menstrual bleeding occurs until menopause, which is the cessation of those cycles. This cycle is initiated by rising gonadotropin (follicle-stimulating hormone [FSH]) levels, causing a cohort of ovarian follicles to grow, develop, and secrete estrogen in the form of estradiol (E2). Eventually, most of these egg follicles atrophy, leaving one egg follicle to become dominant and secrete larger and larger amounts of estradiol (see Figure 4.2). Once the egg is mature, rising estradiol levels trigger the surge of another hormone, luteinizing hormone (LH), which causes the release of the mature egg through the process of ovulation. Estrogen levels fall, but the empty egg follicle, now known as the corpus luteum (“yellow body”), secretes the hormone progesterone (and small amounts of estradiol) to prepare the body for pregnancy (Cable & Grider, 2023). The corpus luteum is hormonally active for about 14 days before it degenerates and triggers the next menstrual period if pregnancy has not occurred. If conception does occur, the corpus luteum will continue to secrete progesterone until the placenta is mature enough to support the growing pregnancy.

The mature egg is released into the abdomen and is gently swept by the fimbriae, finger-like structures, into the infundibulum of the fallopian tube, the small tube that allows the passage of the egg from the ovary to the uterus. Small cilia and gentle muscular contractions, called peristalsis, move the ovum down toward the uterus, which it enters just below the fundus. In most cases, fertilization with a single sperm cell occurs in the distal third, or ampulla, of the fallopian tube. The egg is viable for only about 12 to 24 hours after ovulation (Conception: How it works, n.d.). After that time, it begins to disintegrate if fertilization has not occurred.

Fertilization

The penetration of an ovum by a single sperm cell is called fertilization. When that occurs, the membrane of the ovum, the zona pellucida, becomes impenetrable to other sperm cells (Conception: How it works, n.d.). This process triggers a series of other reactions:

• completion of the second meiotic division of the secondary oocyte
• formation of the female pronucleus from the nucleus of the secondary oocyte
• formation of the male pronucleus from the head of the sperm
• degeneration of the tail of the sperm
• fusion of the two pronuclei and combination of the two sets of chromosomes to form the diploid number

All these reactions occur in the fallopian tube, and once they are complete, the fertilized egg is called a zygote. As the zygote begins to travel down the fallopian tube toward the uterus, a series of mitotic divisions occur that cause the single-celled zygote to become two cells, then 4 cells, then 8, and finally 16 cells, a solid ball of cells called a morula. The zygote does not increase in size during these cellular divisions, so the daughter cells become progressively smaller (Figure 4.6). It takes about 4 days for a fertilized egg to form a morula after fertilization (Khan & Ackerman, 2023).

Figure 4.6 Fertilization and Cell Division Cell division occurs rapidly after fertilization and continues while the zygote travels from the fallopian tube to the uterus. (modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

As the morula floats in the uterus, fluid begins to enter the intracellular space and separate the morula into two distinct parts. Eventually, the morula develops into a blastocyst on about day 5 after fertilization. The inner cell mass contains stem cells, while the outer layer of cells is the trophoblast (Rehman & Muzio, 2023).

Implantation

Implantation occurs most often in the fundus of the uterus around 5 to 6 days after fertilization (Conception: How it works, n.d.). As the zygote reaches the uterine wall, the trophoblast cells surrounding the blastocyst begin to push away the endometrial cells, allowing the blastocyst to burrow into the lining of the uterus. The trophoblast now begins to secrete enzymes that allow it to become completely buried in the endometrial lining, a process known as implantation. This can cause the blood vessels at the site of implantation to break down slightly, sometimes causing spotting known as implantation bleeding.

Chorionic villi are long, finger-like projections that extend from the trophoblast into the endometrium. They facilitate the exchange of oxygen, nutrients, and waste products through the placenta. The zygote officially becomes an embryo after implantation, from about day 15 until week 8 of pregnancy (Oliver & Basit, 2023).