Getting Pregnant : The Basics
WHEN YOU CONCEIVE
A baby is conceived when an egg cell is fertilized by a sperm cell and successfully implants in your uterus. You were born with a lifetime supply of immature eggs stored in your ovaries. In order to become a baby, an egg must first mature and be released from your ovary into your fallopian tube. This process is called ovulation.
If you have a typical menstrual cycle, you ovulate once per month, about every 28 days. Ovulation begins when a group of immature egg cells start to develop in fluid filled sacs called follicles. One follicle becomes dominant and continues to mature while the other follicles stop developing and degrade.
When the dominant follicle is ready, it ruptures and releases a mature egg into your fallopian tube. The ruptured follicle then becomes a structure called the corpus luteum, which secretes hormones that prepare your body to support a pregnancy.
About 20% of women can feel ovulation. For some women, ovulation is painful, while others only notice slight cramping each month. This is called mittelschmerz. Don’t be concerned if you never experience mittelschmerz, 80% of women don’t feel a thing!
Sometimes, two (or more!) follicles develop fully and release mature eggs into your fallopian tubes. If multiple eggs are released, successfully fertilize and implant, you may become pregnant with twins.
As soon as a mature egg enters your fallopian tube, the clock begins ticking. The egg has a 24 hour window in which to meet a sperm cell and become fertilized.
Sperm cells are contributed by the man and are found in his semen. The number of sperm cells in his semen varies, but it’s possible for as many as 600 million sperm cells to be delivered per ejaculation. Average sperm count is estimated at 40 million to 300 million sperm per ml of semen. A minimum of approximately 20 million sperm per ml are needed for fertility.
If the egg finds healthy sperm in your fallopian tube, one sperm cell will penetrate the protein coating surrounding the egg. As soon as the egg has been pierced by a single sperm cell, a chemical “shell” is formed around the egg and no more sperm can enter. Now that a sperm cell has joined with the egg, all of the genetic information is available for the formation of a new person. Congratulations, you have conceived a baby!
If the egg does not meet any healthy sperm during it’s short fertile window, it will pass through your system and no pregnancy will occur. About two weeks later your period will start and the cycle begins again.
IS YOUR BABY A BOY OR A GIRL?
When a sperm cell and egg successfully unite, the genetic blueprint for your baby is complete. Egg cells contain only X chromosomes. Sperm cells can have either X chromosomes or Y chromosomes. If a sperm with X chromosomes joins with the X chromosomes in the egg, a baby girl is conceived. Her chromosomes are XX. If a sperm with Y chromosomes join with the X chromosomes in the egg cell, a baby boy is conceived. His chromosomes are XY.
The X and Y sperm differ slightly in size and strength. You may be able to influence the sex of your baby by using gender selection techniques while you try to conceive.
The fertilized egg, now called an embryo, begins a 3 day journey to your uterus where it will implant and develop into a baby. During this time, your embryo’s cells are dividing and growing. The corpus luteum (formed from the ruptured follicle still in your ovary) has been busy secreting estrogen and progesterone which prepares the lining of your uterus, the endometrium, for the arrival of the embryo.
Once your embryo successfully navigates to the uterus, it burrows into the the endometrium. This process, called implantation, is the final step in conception. After implantation, the embryo begins secreting hCG, (Human chorionic gonadotropin) commonly known as the pregnancy hormone. hCG is the hormone that is excreted in your urine when you are pregnant and causes a pregnancy test to register positive.
WHEN SOMETHING GOES WRONG
Unfortunately for women trying to conceive, many embryos don’t become babies . It is estimated that 60% to 80% of fertilized eggs do not successfully implant. Most of these embryos pass long before a pregnancy could be detected and your period is not delayed. Sometimes the implantation process begins, but the embryo stops developing. In this case, your period may be a day or two late. These very early miscarriages are sometimes called chemical pregnancy.
Rarely (occurring in about 1 in 50 pregnancies), the embryo will implant into the fallopian tube instead of the uterus. This is called a tubal pregnancy, or ectopic pregnancy. The baby cannot develop properly outside of the uterus, so ectopic pregnancies always end in miscarriage.