Young, Hip & Not Ready for Kids: Oocyte Vitrification

B y : Marlane Angle, PhD

Almost any young woman under the age of 40, living in the United States, has grown up with the idea that she can have it all: successful career, fulfilling marriage, a couple of happy kids, and usually in that order. For many young women, this means spending their twenties acquiring wealth and Mr. Right, while delaying the start of a family until well into their thirties. Unfortunately, while our culture may view this as an acceptable family building plan, our biology does not.

Physically, we haven’t changed much from the days when women gave birth to their first children while in their teens. A healthy young woman could live long enough to have many children, thus ensuring that at least some of them would survive an array of childhood diseases to reach adulthood.

Today, the average age for the first child in the United States has increased from 21 in 1970 to over 25 as of 2005. In addition, the birth rate for women 30-34 years of age has risen 21%
over the same period, while the birthrate for 40-44 year olds has risen a staggering 70%. These numbers confirm that women are waiting longer and longer to have their children.

Unfortunately, accompanying these numbers are studies showing that as women age, their chance of getting pregnant decreases, and their risk of a miscarriage rises. Statistical
data from the Center for Disease Control documents fertility rates for women in their twenties to be about 10-25% per month, but these chances drop to only 5% for women over
forty. Miscarriage rates are 5-10% for women in their twenties but rise to 33% for women in their early forties. Down’s syndrome and other chromosomal abnormalities occur in about 1 in 1200 pregnancies for women in their twenties but rise to 1 in 38 for women in their forties.

These scary facts are the direct consequence of what happens to eggs as they sit in the ovaries. Women have all of the eggs they will ever produce by the time they are born. At birth a woman has about 1 to 2 million eggs. Throughout her lifetime a woman loses eggs. By the time she reaches puberty, most women only have about 400,000 eggs left, and they will lose up to 1000 eggs per month for the rest of their reproductive lives from a process called atresia.

To make matters worse, those eggs that are left as a woman ages, change with time. Their genetic material, the chromosomes, becomes sticky. Normally, each month one immature egg will be “chosen.” It will be rescued from atresia and will continue on to ovulation. During that time, the events that regularly keep the eggs small and stop them from maturing each month will be reversed, and the egg will begin to develop. Part of this developmental process is called meiosis. Before meiosis, the egg has two distinct sets of chromosomes. But at the time of fertilization, the egg needs to have only one set because the sperm will bring a set of chromosomes with it, ensuring that the baby will have chromosomes from both mother and father. Therefore, during meiosis, the chromosomes in the nucleus separate, and the egg kicks the extra chromosomes out into a little structure called a polar body. Polar bodies are like little garbage sacks of genetic material waiting to be taken away.

But if the chromosomes have become sticky, some bits of chromosomes can stick to each other. This means the egg may end up with more than its share of chromosomes compared to the polar body, or conversely, more of the chromosomes may end up in the polar body where they don’t belong. Many of the syndromes found in newborns are the result of too many bits of chromosomes left in the egg during meiosis (Down’s syndrome, 3 copies of chromosome 21), or not enough chromosomal bits left in the egg (Turner’s Syndrome, no X chromosome).

Several studies that have looked at chromosomes in eggs from women of all ages have shown that women in their twenties can have as many as 60-80% of the eggs in their ovaries that are normal, but by age forty, only 10-20% will be normal and 80-90% will be abnormal. This high percentage of abnormal eggs explains why women who are older have more difficulty getting pregnant, miscarry more often, and have more babies with these kinds of chromosomal disorders.

So, what is a young woman to do? Have children at a time she doesn’t want them, or isn’t financially prepared for them? Or should she roll the dice and hope that she will be one of the fortunate ones who still have normal chromosomes and a large enough group of eggs to ensure a healthy pregnancy after development of a career and finding “Mr. Right?”

An alternative that should be considered by any young woman is the choice to freeze her eggs while young and keep them for the future. The most successful way to freeze eggs today appears to be by a process called vitrification or ultrarapid freezing. Once eggs are vitrified, scientists don’t know how long they can be frozen, but we speculate that they should be good for decades based on some of the information about how long frozen embryos – or fertilized eggs – can be stored. Eggs could be vitrified at a time when a young woman will have the lowest chance of chromosomal problems and therefore, the highest chance of fertility. Her vitrified eggs would then be available for her use whenever she decides that the time is right for her.

Freezing eggs is not without a certain risk and cost. The process requires a woman to go through the initial steps of an In Vitro Fertilization cycle. She will have to take medicines to stimulate growth of her follicles and rescue many of those eggs that would normally undergo atresia. She will require an egg retrieval procedure to remove them from the follicles. And finally, not all eggs will survive the thawing/warming process. These procedures can cost about $10-15,000, although this price is decreasing over time.

Despite the cost, eggs tucked away in cryostorage can be like money in the bank. They provide an opportunity for women who know they will want children in their future to ensure they have that choice, whether Mr. Right has appeared or not.

“An alternative \that should be considered by any young woman is the choice to freeze her eggs while young and keep them for the future.”