In 1978, Louise Brown became the first baby conceived in a laboratory through assisted reproductive technology. As the first person to be born through in vitro fertilization (IVF), she was called a test-tube baby. Fertility starts to decline for women from about the age of 30, dropping down more steeply once a woman reaches the age of 35. As women grow older the likelihood of getting pregnant falls while the likelihood of infertility rises. Many women in their mid-30s want to have children, so they often turn to fertility therapy, such as in vitro fertilization. Five million babies have already been born this way and half of this number were born just since 2007!
Women start making their own eggs while they are still in the womb. By 20 weeks’ gestation the tiny developing ovaries in a human fetus contain about five million eggs. For reasons that are still unclear, more than two-thirds of these newly made eggs degenerate in the following months, leaving a much smaller supply of eggs at birth. Egg numbers at birth range anywhere from half to one million. The eggs present at birth constitute the only supply of eggs a woman will have in her lifetime. This stockpile of eggs, which is called the ovarian reserve, is housed in structures called primordial follicles, a resting pool of eggs. Eleven thousand eggs will die every month prior to puberty. As a teenager, a woman has only three hundred thousand to four hundred thousand remaining eggs, and from that point on, approximately one thousand eggs are destined to die each month. The average female life expectancy has increased in modern times, while at the same time the average age at which young girls start menstruating has decreased from age thirteen or fourteen to age ten or eleven. To review, only one of those thousand eggs every month is destined to ovulate.
There is still a lot that we don’t know about the ovary, as it is a complex and versatile organ. Most women have two ovaries, one on the right and one on the left, which dispense eggs during their monthly ovulation and usually each ovary alternates taking a turn in releasing an egg. The ovaries produce the female egg cells, called the ova or oocytes. Ovulation occurs when a mature egg is released from the ovary, pushed down the fallopian tube, and is made available to be fertilized. Previous research had suggested that a woman is born with all the egg cells she will ever have in her lifetime. In the last few years, research has found stem cells within ovaries that when grown in the lab will generates immature egg cells which are capable of producing new eggs during your reproductive years. Stem cells, found in embryos and certain adult body tissues, have the potential to grow into many different types of cells. Age remains an important factor because although your body produces new eggs even as you age, the housing for your eggs becomes less ideal with age. Although it is very complex and still experimental, an induced form of stem cells can be obtained by treating mature cells with a cocktail of reagents in the laboratory. Women may create new eggs throughout their reproductive years, thus challenging a longstanding tenet that females are born with finite supplies. Women now have more freedom, because even if they are told that their odds of getting pregnant are low because their eggs are “old,” there’s still hope of conception, as long as their body is producing new eggs.
The ovulation cycle begins in the brain, in the hypothalamus, a region of the brain that connects the nervous and endocrine systems and releases the ovulation hormone. That hormone then triggers the pituitary gland, also in the brain, to produce other hormones, which stimulate your ovaries to produce still other hormones (estrogen and progesterone) that prompt ovulation. During the first week or so after your period begins, both ovaries are hard at work growing follicles that could become mature eggs, but usually only one follicle makes it to ovulation to release an egg. The rest degenerate over the six-to-eight-week development phase, so a woman actually ovulates only about 400 eggs during her reproductive life. This is about 1% of the pool of follicles ever produced.
Around day 7, one egg becomes the dominant egg as a dominant follicle is selected from the cohort of growing follicles, while the other follicles in both ovaries take a load off, eventually degenerating. Follicle size increases over time causing that one egg to become destined to ovulate, growing big enough to release a mature egg and develop as the single dominant follicle at mid-cycle, on day fourteen. After ovulation, that follicle becomes a corpus luteum, which begins to secrete progesterone. Following the release of the egg and subsequent fertilization, the follicle seals itself off and forms what is known as a corpus luteum. This mass of cells helps produce the hormone progesterone during early pregnancy. The corpus luteum will continue to produce progesterone until the fetus is producing adequate levels to sustain the pregnancy, which usually occurs between 7 and 9 weeks of pregnancy. Such is the life of the dominate egg, having the potential to either ovulate its egg into the oviduct at mid-cycle to be fertilized, or to die by atresia.
These otherwise “lost” eggs are the ones that are matured, can be retrieved and preserved with an egg freezing for later use. The first step to achieve in vitro is for the woman to produce eggs. Women are usually given fertility medicine or hormones to get the ovaries to produce multiple eggs increasing the odds of fertilization. A lot of these medications are self-injectable and some women receive up to 90 shots in one cycle. When the eggs are ready but not yet released during ovulation, a hormone is given to the woman to cause the egg to mature and 36 hours later, the eggs are taken out. A very thin needle is inserted through the upper vaginal wall so fluid can be removed from the follicles with gentle suction. The egg is then isolated from the follicular fluid and placed in a culture dish packed with nutrients. Sperm is mixed with the egg to fertilize it, which may sometimes be injected directly into the egg. The Petri dish with eggs and sperm is moved to an incubator at 37 degrees for 24 hours and monitored.
About 50% of the eggs will fertilize and even fewer of them will develop to make good embryos. When a sperm and egg meet they form a full genetic quota, with half our DNA coming from our mother and half from our father. Recently scientists have shown embryos in mice could be created from cells which carry all their chromosomes meaning that in theory, any cell in the human body could be fertilized by a sperm, which is a lot for my brain to handle, knowing that medical science may be able to bring anyone with enough money a baby. While there is something deeply humane about the idea that people have the right to be parents, we all need to place more value on the life of any cantankerous cuties that result.
IVF clinics have sprouted across the globe, and now account for over 60,000 births annually in the USA. There are scientific, political, religious and ethical implications involved with in-vitro fertilization and because it is getting so popular, there may also be some espionage spying issues as well.
Written for Daily Addictions prompt Week #32 – Humane, for FOWC with Fandango – Handle, for August Writing Prompts – Cantankerous cuties, for Sheryl’s A New Daily Post Word Prompt – Dispense, for Ragtag Community – Freedom, for Scotts Daily Prompt – Create, for Weekly Prompts – Review and for Word of the Day Challenge Prompt – Spying.