How to Conceive a Pregnancy

Fortunately for most of us, conceiving a child is as simple as what was taught to us in sex education class. Potential parents don’t have to consciously think about the microscopic interactions necessary between sperm and egg in order to make a baby. Half of couples achieve a pregnancy by the third month of trying of unprotected intercourse. Unfortunately, not everyone becomes a parent so easily. One out of 8 couples fails to conceive a successful pregnancy despite trying for an entire year. These couples are advised to seek medical attention to search for a reason for their troubles. Understanding the nuts and bolts of human fertility becomes very important for these couples.

The entire process of producing sperm, ripening eggs, and getting the two to meet to form an embryo that will grow in the womb is a carefully orchestrated process in humans.

The egg. A woman is born with about a million tiny eggs in her ovaries. She can never make any new eggs after that time. By the time she reaches puberty only about 200,000 eggs remain. Every day a certain number of eggs wither away. Beginning at puberty one egg per month will mature to the point where it can be fertilized. The egg is contained in a fluid-filled egg sac called a follicle. The follicle grows to about one inch in diameter before it ruptures – releasing the egg in a process called ovulation. Ovulation typically occurs 14 days before her next period is due. Cycle lengths of 25-34 days are considered normal. A woman may get clues that she will be ovulating within the next 3 days by noticing an increase in the amount of stretchy cervical mucus that resembles uncooked chicken egg-white.

The sperm. Sperm are produced in the male’s testicle beginning at puberty. New sperm are constantly being made throughout the man’s life. It takes about 2 ½ months for a sperm to be made from start to finish. The mature sperm are stored in the epididymis (a tube near the testicle) until ejaculation occurs – at which time they are transported out the penis after mixing with secretions from the prostate and other glands to form what is semen. Normally there are at least 20 million moving sperm in the ejaculate. The sperm in the epididymis are usually sufficiently replenished within 24 hours of ejaculation.

The meeting of sperm and egg. When the semen is deposited in the vagina, the sperm swim into the mucus which resides in the woman’s cervix. The cervix is the mouth of the uterus. The rest of the semen may leak out of the vagina. The sperm can survive in the mucus for up to 5 days; however, they lose a bit of their vigor after 48 hours. This is why conception is more likely to occur if sexual relations occur at least every other day during the fertile time. Some women utilize an over-the-counter “ovulation predictor” kit which detects a surge in the LH hormone that precedes ovulation to help them with the timing in their busy schedule. Meanwhile, a proportion of the sperm are swimming into the uterus and traveling up both fallopian tubes where they await the arrival of the woman’s egg. The ovulated egg is picked up by the end of the fallopian tube which can be thought of as a sort of vacuum sweeper. The fallopian tube serves as a conduit for the egg to travel from the ovary to the uterus. The fallopian tube is also the site where the egg usually encounters the invading gang of sperm.

Fertilization. For the process to work, the egg must encounter sperm within 24 hours after ovulation. One sperm should penetrate the shell around the egg. Once this happens the shell alters itself to prevent any other sperm from entering. Now the DNA (the genetic material contained within the chromosomes) from the sperm join with the DNA of the egg. Together they make up the full complement of genes needed to create a human. The process is called fertilization.

Implantation. The fertilized egg (also called an embryo) must begin dividing into many cells as it grows. Typically the embryo reaches the interior cavity of the uterus 4 days after fertilization occurred. The lining of the uterus has been made hospitable for the embryo by 2 hormones (estrogen and progesterone) produced by the ovary. If the embryo has the stamina to implant in the lining of the uterus and keep growing, then the woman misses her period and a positive pregnancy test is detectable about 14 days after ovulation.

What can go wrong and how can it be corrected?

Obviously there are many steps in the process where things can go awry. At least 5 % of men in the population have insufficient numbers of moving sperm in their ejaculate. Semen can lack sperm if there is an obstruction in the tube that transports the sperm from the testicle to the outside world. Most of the time low sperm concentrations are due to a problem in the manufacturing of the sperm. Often no clear reason is found for the low production. However, the use of steroids popular among some body builders commonly depresses sperm production for several months even after the steroid is discontinued. Depending on the severity of the sperm deficiency, pregnancy can be achieved by the use of inseminating the sperm directly into the uterus or through the more labor-intensive process of in-vitro fertilization. In the most severe cases, where no sperm can be found even in the testicle, donor sperm can be purchased from a sperm bank.

Perhaps the most common fertility problem encountered in women is inconsistent maturation of the egg. The delicate balance of hormones that govern the egg maturation can often be restored with the correct use of various fertility medications such as clomiphene (clomid), tamoxifen, injectable gonadotropins (such as menopur, gonal F, or follistim), and sometimes metformin (Glucophage). If a woman has run out of eggs (premature menopause) then the only chance for her to carry a pregnancy is to use donated eggs. If the fallopian tubes are blocked, then sperm and egg are unable to meet. Treatments to overcome this problem include surgical correction of the tubes or the use of in-vitro fertilization. There are conditions that can cause more subtle defects in the ability of the egg to reach the tube. Scar tissue surrounding the ovary is one such condition, and endometriosis – which sets up a toxic reaction to the ovulated egg – is another. Minimally invasive surgery such as laparoscopy is sometimes used to search for and to eradicate endometriosis or scar tissue, especially in women who have pelvic pain, worsening menstrual cramps or ovarian cysts.

Armed with this basic knowledge of human reproduction, potential parents who are having trouble making a baby can better negotiate the emotional journey through the medical evaluation and treatment of infertility to achieve the dream of building their family.


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