2.2: Reproductive Systems and Conception
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Learning Objectives
By the end of this section, you will be able to:
- Describe the basic anatomy and functions of the female and male reproductive systems
- Explain how conception takes place
- Identify various pathways to parenthood
Alex and his husband Brian share a dream of having a family of their own. Aware that they may face challenges, they research options and seek advice from friends and family. Ultimately, the couple decides to explore assisted reproduction and surrogacy. They attend fertility clinics, consult with specialists, and determine that they will use Alex’s sperm due to a genetic disorder on Brian’s side. The final step is meeting with potential surrogates. Each step is accompanied by its share of uncertainties. After a series of hopeful moments and a few heart-wrenching setbacks, Alex and Brian finally receive the news they have been yearning for—they are expecting a child.
The organs and hormones that make up the reproductive systems of biological males and females work to create a new human being, whether the biological parents conceive on their own, use reproductive assistance, or engage a surrogate or sperm or egg donation. Puberty determines when reproductive systems are mature enough to create and, in the case of biological females, to support the growth of another life. In this section, you will learn about the basic components of the reproductive systems and how conception occurs.
The Female and Male Reproductive Systems
The biological male and female reproductive systems have many similarities. Both males and females have gonad s (testes or ovaries), and both produce gamete s (sperm or ova). Further, both reproductive systems have similar internal features that allow for gametes to be transported—the fallopian tubes and vans deferens—as well as external features that facilitate sexual intercourse and orgasm (penis and vulva) (Figure 2.12).
The Female Reproductive System
The main components of the female reproductive system are the ovaries, fallopian tubes, uterus, cervix, and vagina. The ovaries contain ova, or eggs, which are gamete cells carrying the genetic information of the biological female. Biological females have two ovaries, one on each side of the uterus. Each fallopian tube runs from an ovary to the uterus and transports fertilized ova to the uterus. The uterus , also called the womb, is the organ in which the fetus develops. At the lower end of the uterus is the cervix, which connects the uterus with the vagina , the muscular canal that leads to the outside of the body. The vagina is not visible on the outside of the body; however, the vulva , consisting of the external aspects of the female reproductive system (including the labia, clitoris, and vaginal opening), is visible.
Most biological females experience a menstrual cycle , a monthly process of hormonal shifts that make conception possible, lasting approximately twenty-eight days. This cycle has three phases: follicular, ovulatory, and luteal. During the follicular phase, several eggs develop until one (or more) is released in a process called ovulation. Ovulation typically happens around the fourteenth to the sixteenth day of a cycle (day one of each cycle is the first day of the preceding period) although much variation in the timing exists among individuals (Grieger & Norman, 2020). During the luteal phase, the uterus creates a layer called the endometrium, which is rich with nutrients to help sustain a fertilized egg. If the egg is not fertilized, it dissolves, and the endometrial lining of the uterus is shed during menstruation. The cycle then begins again.
The Male Reproductive System
The major parts of the male reproductive system are the testes, penis, vas deferens, urethra, and ejaculatory ducts (refer to Figure 2.12). These components help create and maintain the health of sperm, which are the male gametes that merge with ova during fertilization, causing conception. The male reproductive system also assists in the introduction of sperm into the female reproductive tract during intercourse.
The top of the penis marks the beginning of the male urethra , which releases sperm at the moment of ejaculation, or male orgasm. For conception to occur during vaginal intercourse, the penis and urethra must deposit sperm into the vagina. The scrotum is located below the penis and contains the testes , which produce sperm and testosterone. The vas deferens transports sperm from the testes to the urethra. Near the back of each testis is the epididymis, a tube that stores sperm until they are mature.
During any type of sexual activity, sperm is moved from the epididymis, via the vas deferens and ejaculatory duct, to the urethra. The urethra, in males and females, is also responsible for releasing urine. However, increased blood flow from arousal prevents urine from flowing through the urethra during sexual activity.
Conception
The union of sperm and ovum, or gametes, to create a new organism is called conception (Figure 2.13). For conception to occur, the gametes from a biological male and female must meet. This occurs most commonly during vaginal intercourse when sperm is ejaculated into the vagina.
The release of the egg is mediated by hormones, specifically, luteinizing hormone. A hormone is a chemical released by glands within the human body that alters and controls aspects of bodily function. If an egg is fertilized, it typically travels down the fallopian tube to the uterus where it implants into the uterine wall and eventually develops into an embryo before eventually developing into a fetus . The female’s body also releases the hormone progesterone (or it is provided if using fertility treatments), which helps thicken the endometrial lining and is necessary for successful implantation of the fertilized egg and thereby pregnancy.
Once sperm enter the vagina, they travel through the cervix and cervical mucus to reach the uterus. Sperm encounter acidic conditions in the vagina and create a coating that protects them and helps them to survive in that environment (Suarez & Pacey, 2005). Sperm that survive the journey to the uterus will be directed toward the fallopian tubes via contractions in the uterus. Sperm can survive up to five days within the female reproductive system, though the egg is able to be fertilized for only about twelve hours after release (University of California San Francisco Health, 2024). Many sperm will travel to the fallopian tubes to reach the egg, but only one sperm can penetrate it (Suarez & Pacey, 2005). Once fertilization occurs, the egg becomes impenetrable and the remaining sperm die off.
Pathways to Parenthood
For people to conceive, the likelihood of achieving pregnancy varies due to multiple factors including the age, fertility, and health of the biological parents. Many people conceive without actively planning or intending to; still others take direct steps to delay or prevent pregnancy. Many couples can get pregnant within one year of trying to conceive, but only about 30 percent of people under age thirty years get pregnant during the first three months (Taylor, 2003; WHO, 2024). If someone has been trying to conceive for at least one year without success, they may have fertility challenges.
Today's medical professionals can assist many people with fertility concerns. Many types of families, including single individuals and individuals in same-sex relationships, have pathways to parenthood including assisted reproductive technology (ART) or the use of donor eggs and/or sperm. For those who do not wish to undergo such treatments (or for whom the treatments aren’t successful), other routes to parenthood include surrogacy and adoption. These options are expensive, however, and are often not covered by insurance.
Causes of Infertility
The clinical term infertility describes a condition in which someone has not successfully conceived after trying for at least one year. According to research, approximately 15 percent of females and 11 to 12 percent of males have some form of infertility (Borumandnia et al., 2022; Nugent & Chandra, 2024). The cause may be fertility issues in the female, the male, or both parties, or unknown causes (Borumandnia et al., 2022; Nugent & Chandra, 2024). Many fertility challenges can be addressed medically; however, success of those treatments varies among individuals.
Male infertility can be caused by hormonal irregularity and blockages within any of the organs of the male reproductive system. Or, the sperm may have low motility, preventing them from moving effectively and traveling through the female reproductive tract (Leslie et al., 2024). However, nearly half of all cases of male infertility occur from unknown causes (Leslie et al., 2024).
Intersections and Contexts: Access to Fertility Treatments across the Globe
According to the World Health Organization (WHO), at least one in six individuals across the globe deals with infertility at some point in their life (World Health Organization, 2024). Fertility problems do not discriminate; they can affect individuals at all income levels, all ethnicities, and all ages. What does differ among those dealing with infertility, however, is access to fertility treatment s (World Health Organization, 2024).
According to Fauser et al. (2019; 2024), collecting data about fertility treatments globally has been difficult until recently, because not all nations publish data on their number of fertility centers or assisted reproduction procedures. Most procedures are performed in Asia and Europe, possibly because the associated costs are lower in these regions. Some countries in Europe, such as Denmark, may financially help individuals with the cost of fertility treatments. Africa appears to have the fewest facilities and procedures, possibly due to underreporting, because only forty fertility centers from thirteen of the continent’s fifty-four countries participated in data collection (Fauser et al., 2019; Fauser et al., 2024).
Practitioners of fertility treatments in the United States perform half as many procedures as their European colleagues and charge the highest fees, which are typically not covered by insurance. In vitro fertilization (IVF), a medical intervention to aid in producing a successful pregnancy, can cost more than $15,000 per attempt in the United States. In some countries, age may also be a barrier to fertility treatments. Sweden does not allow women over forty-two years of age to use these methods, and women from Denmark lose access at age forty-six years (Fauser et al., 2019).
Not only can IVF treatments be expensive, but they can also be time-intensive, requiring many visits for lab work and they may involve physical discomfort. This makes the process difficult to take on several levels, even when it is available. In many parts of the world, especially in rural areas, the distance to the nearest fertility clinic may be prohibitive as well. So, while medical ART and the understanding of fertility have grown dramatically, there remains unequal access to helpful resources.
Some common fertility problems for females are blocked fallopian tubes, uterine abnormalities, endometriosis, and polycystic ovary syndrome (PCOS), the most frequent challenge. In PCOS, a hormone imbalance results in higher levels of androgens (sex hormones) that can also cause small cysts on the ovaries and irregular menstruation (Rocha et al., 2019). The fallopian tubes can become blocked for many reasons, including from scar tissue from previous surgery, infections, sexually transmitted diseases, fibroids, and endometriosis (Ambildhuke et al., 2022). Uterine fibroids are abnormal noncancerous growths that may be hereditary and are sensitive to estrogen and progesterone. Though the cause of fibroids is not known, several factors increase the risk of developing them, including family history, obesity, early onset of menstruation, heavy drinking, and race, given that fibroids tend to occur more frequently in Black women (Office on Women’s Health, 2021). Endometriosis is a painful condition in which the uterine lining, the endometrium, grows outside the uterus. In PCOS, a hormone imbalance, results in higher levels of androgens (sex hormones) that can also cause small cysts on the ovaries and irregular menstruation (Rocha et al., 2019). Many of these fertility problems can be detected early and treated through advances in ART.
Fertility Treatments
Most fertility treatments rely on ART (Pakhomov et al., 2021). Some of the most common are ovulation induction , intrauterine insemination , and IVF. Ovulation induction uses medications to stimulate ovulation in individuals who are not ovulating regularly. A doctor will assess the eggs using an intrauterine ultrasound on the tenth or eleventh day of the menstrual cycle. Once the eggs are mature, an injection of human chorionic gonadotrophin (hCg) will be used to stimulate ovulation (Sharma & Balasundaram, 2022).
Intrauterine insemination (IUI) is often helpful when a low sperm count or weak sperm is an issue, or when single individuals or same-sex couples wish to conceive. After ovulation occurs, sperm are placed directly into the uterus. A process called washing ensures the healthiest sperm provided are used (Allahbadia, 2017). The process of in vitro fertilization (IVF) combines sperm with one or more eggs from a biological female in a laboratory and allows them to divide for a time before placing one or more fertilized eggs into the uterus of the patient undergoing treatment (Pakhomov et al., 2021).
All these fertility treatments carry some risks. For example, when using fertility drugs to stimulate egg production, individuals may experience mild side effects (bloating, nausea, hot flashes), or more severe side effects such as ovarian hyperstimulation syndrome (painful swelling of the ovaries) and an increased chance of ectopic pregnancies (in which the embryo implants within the fallopian tube instead of the uterus) (Pakhomov et al., 2021). The use of fertility drugs for these procedures also increases the likelihood of carrying twins or triplets. Finally, higher rates of preterm births, low birth weight, and birth defects (such as spinal bifida, congenital heart issues, cerebral palsy) are associated with ART (von Wolff & Haaf, 2020).
Link to Learning
Learn more about many of the intricacies of the IVF fertilization process in this TED-Ed video.
Surrogacy and Adoption
Some people experiencing infertility may consider surrogacy or adoption (Figure 2.14). In surrogacy , those who wish to become parents partner with someone who is willing to carry a fetus and give birth. Surrogates typically undergo IVF to become pregnant; however, in some cases, it is possible for them to become pregnant using IUI (intrauterine insemination), which allows sperm to be placed directly in the uterus. The implanted embryo may result from the egg and sperm of the couple desiring to be parents or from donor eggs and/or sperm. Some people use agencies to help them find suitable surrogates, and renumeration and coverage of medical expenses are typically included in the legal contract between the surrogate and the prospective parents.
Individuals and couples can also adopt children whose biological parents have voluntarily placed them for adoption or lost their parental rights. Adoption often takes place with the assistance of adoption agencies. Individuals can also foster children through foster care systems in many countries. These children may or may not be eligible for adoption when the placement happens, or they may become eligible later. Other forms of adoption include familial adoption, in which a child is adopted by a relative, and international adoption. International adoption may bring unique challenges depending on qualifications potential parents must meet to adhere to government policies.
Unintended Pregnancies
According to the United Nations Population Fund, approximately 121 million unintended pregnancies occur worldwide each year (Baker et al., 2022). These happen for multiple reasons, including lack of access to contraceptives, reproductive care, and/or education and sex education; sexual violence against females; and cultural norms suggesting that women need to have children (Baker et al., 2022).
In the United States, around 40 percent of all pregnancies are reported as being unintended (CDC, 2024). However, the number varies dramatically across different groups. Adolescent pregnancies (in those aged fifteen to nineteen years) account for the majority of unintended pregnancies; women between eighteen and twenty-four years of age who had incomes at or below poverty level, did not complete high school, and were Hispanic or Black also had high numbers of unintended pregnancies (U.S. Centers for Disease Control and Prevention, 2024).
It Depends: Is Pregnancy Prevention Common Knowledge?
A recent report from the United Nations Population Fund estimated that at least half of all pregnancies worldwide each year are unintended (Baker et al., 2022). This means millions of women are conceiving who did not plan to get pregnant. According to Bearak et al. (2020), around 61 percent of unintended pregnancies worldwide in women between ages fifteen and forty-nine years end in abortion s that are unsafe, illegal, or both. In developing countries, unsafe abortions resulted in nearly 200,000 maternal deaths between 2003 and 2009. They also forced the hospitalization of seven million women and likely cost more than $550 million in follow-up treatment (Bearak et al., 2020).
Among the reasons for unintended pregnancies globally are misinformation about contraception and lack of access to contraceptive methods and education. Many young people all over the world depend on friends for advice about preventing pregnancy because discussing the topic with family can be difficult. Without access to sex education, myths and misinformation abound, including the idea that contraceptives (such as birth control pills or intrauterine devices [IUDs]) may harm future fertility or decrease sexual desire, that early withdrawal or urination after intercourse prevents conception, that certain positions may decrease the chance of conceiving, and that avoiding intercourse around the time of ovulation prevents pregnancy (Lundsberg et al., 2014; Mwaisaka et al., 2020). Lundsberg et al. (2014) found that more than 40 percent of U.S. women in their study did not know when ovulation typically occurs.
These and other misconceptions can be dispelled with sex education and increased access to information about contraception. According to Lundsberg et al. (2014), most women in their study said they would ask their women’s health-care provider about pregnancy, followed by websites; however, most admitted not asking their provider any questions. Though many had concerns about their fertility, pregnancy and conception were thought to be private and awkward to discuss. Providing more access to sex education and to contraceptives may help decrease the high number of unintended pregnancies globally, as well as making sex education more common.
Birth Control and Family Planning
The use of contraception , a method to prevent conception, has been steadily increasing each year on every continent except Oceania and North America, although North America reports the highest use of contraception of all continents (Ponce de Leon et al., 2019). The largest increase in contraceptive use occurred in Africa, although there it remains the lowest rate of all continents (Ponce de Leon et al., 2019). That increase has been slow, likely due to limits on contraceptive choices, lack of access to reproductive health services for individuals living at or below the poverty level, cultural or religious resistance, and even bias against some methods among reproductive health providers (WHO, 2023).
In the United States, common forms of contraception include birth control pills (oral contraceptives), IUDs, birth control implants, contraceptive patches, injections of hormones such as Depo-Provera, external condoms, and vasectomy. Other less commonly used forms include internal condoms, spermicides, and sponges or diaphragms. Currently, the only form of permanent birth control available to males is vasectomy . Vasectomies are one of the most effective forms of birth control and carry a very low risk of negative side effects compared to all other contraception types (Araújo et al., 2022). While people sometimes have anxiety about this procedure, evidence indicates vasectomy is safe and does not negatively affect sexual function (Yang et al., 2020). Each type of contraception has a different level of effectiveness and different side effects (Table 2.4).
| Type of Contraception | Description | Success Rate at Preventing Pregnancy (%) |
|---|---|---|
| Vasectomy | Surgical procedure where the tubes carrying sperm are cut and sealed | 99 |
| Birth control implant | Device placed under the skin in a female | 99 |
| Tubal ligation or salpingectomy | Surgical procedure where the fallopian tubes are closed off or partially or fully removed | 99 |
| intrauterine device (IUD) | Device placed into uterus by a doctor | 99 |
| Birth control pill | Hormone pills taken daily | 93 |
| Birth control patch | Placed on skin of a female, a patch that delivers hormones | 93 |
| External condom | Sheath that fits over the penis to prevent sperm transfer; also helps prevent sexually transmitted infections but comes with a higher likelihood of errors in effective use (Barrett et al., 2021) | 87 |
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